British Ornithologists' Union https://bou.org.uk/ Advancing ornithology Fri, 15 Mar 2024 15:08:33 +0000 en-GB hourly 1 https://wordpress.org/?v=6.4.3 Wings and wellbeing – exploring birds and human health https://bou.org.uk/blog-doyle-birds-and-health/ https://bou.org.uk/blog-doyle-birds-and-health/#respond Mon, 18 Mar 2024 07:30:26 +0000 https://bou.org.uk/?p=78272 How can we highlight the positive links between human health and wild birds for conservation?

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LINKED PAPER
Birds and human health: Pathways for a positive relationship and improved integration. Gray, A., Doyle, S., Doyle, C., Young, J.C., McMahon, B.J.
2023. IBIS. DOI:10.1111/ibi.13290 VIEW

In this era marked by unprecedented biodiversity loss and environmental challenges, the integrated relationships of biodiversity, ecosystems and human health are gaining attention; and the impacts of this biodiversity loss on human health are being realised. We all know just how immense the need for conservation is. However, the effectiveness of any conservation strategy relies on how much value, both objective and subjective, we place on biodiversity in the first place. This is important because leveraging conservation does not always translate to value for humans. To accomplish our collective conservation goals, we need more tangible – perhaps more anthropocentric – leverage points. As we continue to lose biodiversity, concern is rising for human wellbeing and quality of life (e.g. Cardinale et al. 2012). Emphasising the link between biodiversity and human health could help shift the narrative and highlight the value of conservation to us.

Why look to birds?

With growing research into the ‘One Health’ concept – that is, the interdisciplinary approach that appreciates that the health of humans, domestic and wild animals, plants, and the environment are interdependent (Adisasmito et al. 2022) – comes mounting evidence that our health is intricately linked to the health of ecosystems around us. The interconnectedness of wild birds and human health fits in perfectly with this approach.

Nature’s custodians

Birds play a pivotal role in ecosystem balance through pollination and pest control. For instance, hummingbirds are adept pollinators. While feeding on nectar they transfer pollen from flower to flower, facilitating plants’ reproduction. Birds also contribute to pest control services which support agricultural production – in some cases removing the need for pesticides that are potentially harmful for human health (Pejchar et al. 2018). Insectivorous species like flycatchers are natural pest controllers by preying on insects, helping regulate populations, preventing pest outbreaks that could negatively impact crops. Not to mention raptors keeping rodent numbers in check can be as effective as the use of rodenticides, with the added bonus of reduced cost to the farmer. In this way you could say that while keeping our ecosystems clean and functioning, birds are like nature’s custodians.

Food, medicine and culture

From the nutritional benefits gotten from wild bird meat to the income provided by bird-related ecotourism, wild birds have a tangible effect on human life globally. Many cultures use birds such as vultures in sorcery and spiritual custom and consume them because of their cultural significance (e.g. Henriques et al. 2018). Wild birds are also used in traditional medicine; and in the lab, cells from Turkey Vultures have even been found to kill human cervical cancer cells (Del Rosario Jacob-Salcedo et al. 2013)!

However, it’s important to highlight that the use of wild birds for medicinal purposes raises concerns for ethics and exploitation. It may even pose a threat to conservation efforts if left unregulated. Education and the promotion of sustainable, evidence-based healthcare are always needed.

Not just the physical

Beyond our physical health, being in the presence of wild birds can have profound effects on mental wellbeing. Many of us use bird-related recreation for mood lifting and relaxation, with birdwatching being linked to reduced stress, anxiety, and depression (Cox et al. 2017). Birds can even facilitate human connection to nature which is often recommended for human health and wellbeing (e.g. Clark et al. 2019).

Considering public health

Whilst birds have been identified as potential reservoirs for zoonotic diseases (illnesses that can be transmitted between animals and humans), emphasis should be placed on the importance of birds in public health. Wild birds can serve as sentinels, indicating the presence of zoonotic diseases in the environment. Monitoring bird populations such as waterfowl for avian influenza or corvids for West Nile virus, helps authorities predict and respond to potential human outbreaks. Understanding the dynamics of zoonoses in bird populations is critical to prevent future pandemics.

For the future

As we champion biodiversity conservation efforts, we as humans could easily overlook the connections between wild birds and our own wellbeing. However, by embracing the One Health concept, recognising and understanding these links, we could support conservation while also ensuring the future health and wellbeing of humans and the wildlife with whom we share the planet.

References

Adisasmito, W.B., Almuhairi, S., Behravesh, C.B., Bilivogui, P., Bukachi, S.A., Casas, N., Becerra, N.C., Charron, D.F., Chaudhary, A., Zanella, J.R.C. & Cunningham, A.A. 2022. One Health: A new definition for a sustainable and healthy future. PLoS Pathogens 18:6. VIEW

Cardinale, B.J., Duffy, J.E., Gonzalez, A., Hooper, D.U., Perrings, C., Venail, P., Narwani, A., Mace, G.M., Tilman, D., Wardle, D.A. & Kinzig, A.P. 2012. Biodiversity loss and its impact on humanity. Nature 486:59. VIEW

Clark, D.N., Jones, D.N. & Reynolds, S.J. 2019. Exploring the motivations for garden bird feeding in south-east England. Ecology and Society 24:1. VIEW

Cox, D.T., Shanahan, D.F., Hudson, H.L., Plummer, K.E., Siriwardena, G.M., Fuller, R.A., Anderson, K., Hancock, S. & Gaston, K.J. 2017. Doses of neighborhood nature: the benefits for mental health of living with nature. BioScience 67. VIEW

del Rosario Jacobo-Salcedo, M., del Carmen Juarez-Vazquez, M., González-Espíndola, L.Á., Maciel-Torres, S.P., García-Carrancá, A. & Alonso-Castro, A.J. 2013. Biological effects of aqueous extract from Turkey vulture Cathartes aura (Cathartidae) meat. Journal of Ethnopharmacol. 145. VIEW

Henriques, M., Pedro Granadeiro, J., Monteiro, H., Nuno, A., Lecoq, M., Cardoso, P., Regalla, A. & Catry, P. 2018. Not in wilderness: African vulture strongholds remain in areas with high human density. PLoS One 13. VIEW

Pejchar, L., Clough, Y., Ekroos, J., Nicholas, K.A., Olsson, O.L.A., Ram, D., Tschumi, M. & Smith, H.G. 2018. Net effects of birds in agroecosystems. BioScience 68. VIEW

Image credits

Top right: White-rumped Vulture © S Lovell.

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Does eggshell phenotype act as an identity signal? https://bou.org.uk/blog-afm-hirundinidae-maculation-evolution/ https://bou.org.uk/blog-afm-hirundinidae-maculation-evolution/#respond Thu, 07 Mar 2024 07:30:55 +0000 https://bou.org.uk/?p=78000 Sociality and nest environment linked to eggshell maculation in Hirundinidae

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LINKED PAPER
Correlated evolution of eggshell maculation with social breeding and nest type in Hirundinidae. Levin, I. I., Kaufman, S. L., Knaysi, S. E., & Rataezyk, O. G. 2023. IBIS. DOI: 10.1111/ibi.13118. VIEW

Why are some bird eggs maculated (patterned) and others immaculate (non-patterned)? Studies across different species have provided evidence for various functions of maculation including crypsis (camouflage), structural support, mimicry, egg or clutch recognition, and signalling (Underwood & Sealy 2002). It has been suggested that avian eggs are therefore subject to a hierarchy of selective forces which have contributed to their vast phenotypic diversity (Kilner 2006), but there is a lack of consensus on which factors play the biggest role.

A recent study in Ibis examined the correlation between eggshell maculation, social breeding, and nest type in Hirundinidae (swallows and martins) to test for correlated evolution between these traits.

A possible identity signal
Iris I. Levin and colleagues analysed 61 species of Hirundinidae for which they had information on social breeding (social vs. solitary), eggshell maculation (maculated vs. immaculate), and nest type (open cup vs. closed/cavity nest). Instances of conspecific brood parasitism (CBP) had also been reported for eight of the species, although as this behaviour is often challenging to detect it may also occur in others. The diversity of this group in terms of maculation and breeding biology presented an opportunity to investigate if eggshell patterns might act as an identity signal allowing for egg or clutch recognition when birds nest in dense colonies and/or face inter- or intraspecific brood parasitism.

Figure 1. Phylogenetic tree of Hirundinidae including all species with data on eggshell maculation (maculated or immaculate), breeding biology (solitary, social) and nest type (open, closed). Underlined species breed socially and an asterisk denotes documented or suspected conspecific brood parasitism (CBP).

Correlated evolution with social breeding and nest type
The results showed that socially breeding swallows and martins and those breeding in open-cup nests were more likely to lay maculated eggs, and that five of the eight species with documented CBP lay maculated eggs. The correlation between maculation and nest type is consistent with other studies showing that patterned eggs are less likely to be laid by cavity-nesting species (Kilner 2006). It may be that white, immaculate eggs are easier for parents to find in dim environments such as cavity-nests (Lack 1958), while in well-lit environments such as open-cup nests maculation could have evolved to promote recognisability. The correlation between social breeding and eggshell patterns indicates that maculation, coupled with low intra-clutch variation in maculation, may enable females to find their nests in crowded colonies. Maculation may also help with recognition of foreign eggs in cases of CBP, however it has been shown previously that egg rejection based on egg recognition is absent in most taxa with CBP (Lyon & Eadie 2008).

The researchers suggest that future work on other groups with variations in their breeding behaviour and maculation would help to further investigate these research questions, and they also highlight the need for more experimental work geared towards understanding the adaptive value of eggshell maculation as an identity signal.

References

Kilner, R.M. (20o6). The evolution of egg colour and patterning in birds. Biological Reviews 81: 383-406. VIEW

Lack, D. (1958). The significance of the colour of turdine eggs. Ibis 100: 145-166. VIEW

Lyon, B.E. & Eadie, J.M. (2008). Conspecific brood parasitism in birds: a life-history perspective. Annual Review of Ecology, Evolution, and Systematics 39: 343-363. VIEW

Underwood, T.J. & Sealy, S.G. (2002). Adaptive significance of egg coloration. In Deeming, D.C. (ed) Avian Incubation, Behaviour, Environment and Evolution: 280–298. Oxford: Oxford University Press. VIEW

Image credits

Top right: Barn Swallow (Hirundo rustica) nest eggs | Kati Fleming | CC BY-SA 3.0 Wikimedia Commons

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Recent surveys deliver mixed news for India’s vultures https://bou.org.uk/blog-mallord-indian-vultures/ https://bou.org.uk/blog-mallord-indian-vultures/#respond Mon, 04 Mar 2024 07:30:43 +0000 https://bou.org.uk/?p=76781 Populations of Critically Endangered species remain stable but no evidence of recovery

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LINKED PAPER
Recent trends in populations of Critically Endangered Gyps vultures in India. Prakash, V., Bajpal, H., Chakraborty, S.S., Mahadev, M.S., Mallord, J.W., Prakash, N., Ranade, S.P., Shringarpure, R.N., Bowden, C.G.R., Green, R.E.
2024. Bird Conservation International. DOI:10.1017/S0959270923000394 VIEW

The goal of most conservation actions is to have a positive impact on your population of interest. Ultimately, this often involves halting population declines and, hopefully, seeing a recovery in numbers of your target species.

When talking of avian population declines, few recent examples can compare with the plight of Gyps vultures in South Asia. Historically considered some of the most abundant species of large raptor in the world, their populations underwent catastrophic declines from the mid-1990s onwards, as a result of unintentional poisoning by the veterinary drug diclofenac (Green et al. 2007, Prakash et al. 2017). The worst-hit species, White-rumped Vulture Gyps bengalensis, declined by 99.9% in India between 1992 and 2007. As a result, three species endemic to South and South-east Asia, White-rumped, Indian G. indicus and Slender-billed G. tenuirostris Vultures, were classified by IUCN as Critically Endangered.

Diclofenac was banned in India and elsewhere in 2006, since when concerted efforts, including widespread advocacy and education, have been made to ensure the drug remains absent from the vultures’ food supply. Along with these conservation actions, vulture numbers have been monitored on a regular basis to assess whether the efforts are having any impact on the status of populations of these endangered species.

Beginning in 1992, vultures in India have been surveyed along road transects, which involves driving along both major highways, and tracks running through protected areas, and counting any vultures encountered (Figure 1). The eighth such survey, which covered over 16,000 km of roads in 13 states in north, west and central India, was carried out in 2022, and the results have recently been published.

Figure 1. Team from Bombay Natural History Society carrying out road transect surveys in north India © Sachin Ranade

Previous surveys up to 2015 had shown that the rapid declines that White-rumped and Indian and Slender-billed Vultures combined (the latter wasn’t recognised as a separate species until 2002) had experienced from the mid-1990s onwards had begun to slow down, with even some tentative evidence that populations of White-rumped had stabilised (Prakash et al. 2017). Numbers of Slender-billed Vultures have always been too low to quantify a reliable trend for this rare species. Survey results from 2022 confirmed that populations continued to remain stable, including Indian Vulture, which had shown signs of further declines in the 2015 survey (Figure 2).

Figure 2. Indices and trends of populations of White-rumped Vulture (circles) and of Indian and Slender-billed Vultures combined (squares) in northern India, based on counts from road transect surveys, 1992-2022.

Further evidence that populations have remained stable came from analysis of changes over time in the annual population multiplication rate, which was below one (indicating a population decline) in the early 2000s, but which hovered around one (stability) in later periods (Figure 3).

Figure 3. Annual population multiplication rates for White-rumped Vulture in northern India (circles) and Nepal (triangles), and Indian Vulture in northern India. For India, rates were averaged between each consecutive pair of surveys; for Nepal, estimates are for two periods: (2002-2013 and 2013-2018). The horizontal dashed line indicates stable population size.

Unlike in India, in Nepal population indices of WRV and SBV have both shown significant increases over recent years, with population multiplication rates greater than the maximum intrinsic rate likely under optimum conditions (Galligan et al. 2020). Possibly the main reason for these differences is the different status of diclofenac and other vulture-toxic NSAIDs in the two countries. Whereas undercover pharmacy surveys have demonstrated that human formulations of diclofenac are still widely offered for veterinary care in India, the drug has all but disappeared from veterinary pharmacies in Nepal (Galligan et al. 2021). Aided by the early efforts of the Nepal government in instigating a meloxicam (earlier shown to be safe for vultures to consume; Swan et al. 2006) for diclofenac substitution scheme, the vulture-safe drug has become the drug of choice for farmers treating their cattle.

Despite populations of vultures remaining stable since the ban on diclofenac, much work remains to be done to ensure the future survival of these species. With population levels now at a fraction (1/500th and 1/50th of levels in 1992 for WRV and IV, respectively), the species are still in a precarious situation. Although there was welcome news earlier in 2023 that veterinary use of two more vulture-toxic drugs, ketoprofen and aceclofenac, were to be banned in India, there is still no process in place that would prevent new drugs from coming on to the market until their safety to vultures is confirmed. This, along with the continued legal use of the vulture-toxic NSAID nimesulide, and other potentially lethal drugs that have not been tested, leaves vultures still at risk of imminent extinction at the hands of toxic veterinary drugs.

References

Galligan, T.H., Bhusal, K.P., Paudel, K., Chapagain, D., Joshi, A.B., Chaudhary, I.P., Chaudhary, A., Baral, H.S., Cuthbert, R.J., Green, R.E. 2020. Partial recovery of Critically Endangered Gyps vulture populations in Nepal. Bird Conservation International 30:1. VIEW

Galligan, T.H., Mallord, J.W., Prakash, V.M., Bhusal, K.P., Alam, A.B.M.S., Anthony, F.M., Dave, R., Dube, A., Shastri, K., Kumar, Y., Prakash, N., Ranade, S., Shringarpure, R., Chapagain, D., Chaudhary, I.P., Joshi, A.K., Paudel, K., Kabir, T., Ahmed, S., Azmiri, K.Z., Cuthbert, R.J., Bowden, C.G.R., Green, R.E. 2021. Trends in the availability of the vulture-toxic drug, diclofenac, and other NSAIDs in South Asia, as revealed by covert pharmacy surveys. Bird Conservation International 31:3. VIEW

Green, R.E., Taggart, M.A., Senacha, K.R., Raghavan, B., Pain, D.J., Jhala, Y., Cuthbert, R. 2007. Rate of Decline of the Oriental White-Backed Vulture Population in India Estimated from a Survey of Diclofenac Residues in Carcasses of Ungulates. PloS ONE 2. VIEW

Prakash, V., Galligan, T.H.,, Chakraborty, S.S., Dave, R., Kulkarni, M.D., Prakash, N.,  Shringarpure, R.N., Ranade, S.P., Green, R.E. 2017. Recent changes in populations of Critically Endangered Gyps vultures in India. Bird Conservation International 29:1. VIEW

Swan, G., Naidoo, V., Cuthbert, R., Green, R.E., Pain, D.J., Swarup, D., Prakash, V., Taggart, M., Bekker, L., Das, D., Diekmann, J., Diekmann, M., Killian, E., Meharg, A., Patra, R.C., Saini, M., Wolter, K. 2006. Removing the threat of diclofenac to critically endangered Asian vultures. PloS Biology 4:3. VIEW

Image credits

Top right: White-rumped Vulture © S Lovell.

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Water off a duck’s back https://bou.org.uk/blog-montgomerie-preening-oil/ https://bou.org.uk/blog-montgomerie-preening-oil/#respond Thu, 29 Feb 2024 07:30:00 +0000 https://bou.org.uk/?p=76642 The history of our understanding of preening oils and waterproofing

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Frederick II, the Holy Roman Emperor from 1220-1250, knew his birds. His ornithological magnum opus—De Arte Venandi Cum Avibus, in English The Art of Hunting with Birds—was probably the first treatise devoted to the study of birds. Despite his title, based on Frederick’s love of falconry, he describes many aspects of the behaviour, morphology, and ecology of all kinds of birds.

Frederick devoted an entire short chapter to what we now more often call the preen gland or uropygial gland. Here is his whole chapter, translated from the Latin (Wood & Fyfe 1943):

CHAPTER XXXI – OF THE OIL GLAND (PERUNCTUM)

This is a peculiar structure which lies above the tail. It consists of a double gland in the center of which (toward its end) rises a compact, stout elevation resembling a brush. This gland receives fluid oil from the body, which the bird squeezes out with its mandibles, collects, and then conveys to both feathers and talons, in consequence of which they are able better to resist moisture. Rain affects the oiled parts very little but runs off them completely and swiftly. Feathers and claws are thus preserved in good condition. Talons of birds of prey, owing to the noxious character of this oil, inflict more deadly injuries upon and bring about quicker death of their quarry because the wounds they make are toxic.

Birds differ in the amount of glandular secretion produced. Aquatic species as a rule have a larger gland and oil in greater profusion than either neutral or terrestrial birds.

Figure 1. Frederick II and Eagle.

Frederick is remarkably and characteristically perceptive and accurate here. His only mistake is his suggestion that the preen oil of birds of prey is toxic This was eventually corrected in 1678 by the equally perceptive John Ray and Francis Willughby in their monumental treatise on ornithology, The Ornithology of Francis Willughby (Ray 1678; Birkhead 2020). As Schöpffer (1896; cited in Wood & Fyfe 1943) pointed out, two centuries later, a toxic preen oil would probably have killed the very raptors who put it on their talons.

The study of preen glands and preen oils has been quite episodic. In the late 19th and early 20th centuries, there was a flurry of interest in the histology and embryology of the preen gland, and how that varied among species (see Hou 1928ab for comprehensive review). Several authors suggested, for example, that the structure of the preen gland might be a useful taxonomic criterion, particularly for defining genera and families.

Surprisingly, there was also a vigorous debate about the water-repelling properties of the preen oil. Charles Waterton [1782-1865] started this controversy with a series of articles claiming that he had “proof positive that the plumage of the bird has not been lubricated with oil from the tail gland.” and that birds preened only to remove lice from their feathers (e.g. Waterton 1932). Although several ornithologists soon provided evidence that preen oil was needed for water repellency (e.g. Matthews 1861), William Pycraft (1910) disagreed and instead felt that the uropygial was a scent gland, analogous to the scent gland of mammals. A century later we now know that he was insightful if not entirely correct.

Figure 2. White-winged Crossbill extracting preen oil from its uropygial gland © Darroch Whitaker BY SA 3.0 Wikimedia Commons.

Despite some convincing evidence of the waterproofing provided by preen oils (Hou 1928ab), the controversy was rekindled by Eugene Law (1929) and Harry Madsen (1941) both of whom conducted some simple experiments claiming to show that the feather structure alone provided the waterproofing and not the preen oil.

The matter was finally laid to rest in 1954 by William H. Elder [1913-2006], professor of wildlife management at the University of Missouri. In 1947 and 1951, he conducted experimental studies on the oil gland of ducks at the Delta Waterfowl Research Station in Manitoba, Canada. Among other things he showed that the preen oil of ducks (i) contains fatty acids and waxes, (ii) “maintains the water-repellent quality of feathers either directly or by preserving their physical structure”, (iii) is needed to maintain the structure of feathers between moults, (iv) helps to preserve bill condition, and (v) is essential for the survival of free-living ducks. He was uncertain about the role of the uropygial as a scent gland.

The study of uropygial glands lay relatively dormant for the next half century, but in the last 20 years there have been at least 70 publications on preen glands and oils. This renewed interest may have been re-awakened by discoveries about the olfactory capabilities of birds and the influence of olfaction on social behaviours, but also by technological advances in the analysis of preen oils and feather structures. We now know that preen oils have odours that other birds can detect (Grieves et al. 2019) and that they vary among individuals, across seasons, between and among mated pairs (Gilles et al. 2024), and with health and condition. Intriguingly, the preen oils of high latitude nesting sandpipers are less volatile during incubation when they might be detected by mammalian predators (Reneerkens et al. 2002). One thing we also now know for certain is that they are largely responsible for the shedding of water off a duck’s back as Frederick II observed almost eight centuries ago.

Further Reading

Birkhead, T.R. 2023. The Wonderful Mr Willughby: The first true ornithologist. Bloomsbury:London

Elder, W.H. 1954. The oil gland of birds. Condor 66. VIEW.

Gilles, M., Fokkema, R.W., Korsten, P., Caspers, B.A., Schmoll, T. 2024. Preen oil composition of Pied Flycatchers is similar between partners but differs between sexes and breeding stages. IBIS 166. VIEW.

Grieves, L.A., Bernards, M.A., MacDougall-Shackleton, E.A. 2019. Behavioural responses of songbirds to preen oil odour cues of sex and species. Animal Behaviour 156. VIEW.

Hou, H-C. 1928. Studies on the glandula uropygialis of birds. Chinese Journal of Physiology 2.

Law, J.E. 1929. The function of the oil gland. Condor 31.

Madsen, H. 1941. What makes bird waterproof?. Foren. Tidsskr. 35.

Matthews, H.S.R. 1861. Oil-gland in birds. Zoologist 19.

Pycraft, W.P. 1910. A history of birds. Meuthen & Co.:London.

Ray, J. 1678. The ornithology of Francis Willughby. John Martyn:London.

Reneerkens, J., Piersma, T., Sinningh-Damste, J.S. 2002. Sandpipers (Scolopacidae) switch from monoester to diester preen waxes during courtship and incubation, but why?. Proceedings of the Royal Society B 269. VIEW.

Schoepffer, C. 1896. Des Hohenstaufen-Kaisers Friedrich II. Bücher von der Natur der Vögel und der Falknerei, mit den Zusätzen des Königs Manfred. Aus dem Lateinischen übersetzt und versehen mit Originalzeichnungen, sowie einem Wörterbuch der Falknereisprache von H. Schöpffer. [The Hohenstaufen Emperor Frederick II’s books on the nature of birds and falconry, with the additions of King Manfred. Translated from the Latin and provided with original drawings, as well as a dictionary of falconry language by H. Schöpffer]. Paul Parey:Berlin.

Waterton, C. 1832. On birds using oil from glands “for the purpose of lubricating the surface of their plumage”. Magazine of Natural History 5.

Image credits

Top right: Mallard shedding water © George Thomas CC BY NC ND 2.0 Flickr

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Birds in Fruit Farms https://bou.org.uk/blog-zielonka-birds-fruit-farms/ https://bou.org.uk/blog-zielonka-birds-fruit-farms/#respond Mon, 26 Feb 2024 07:30:22 +0000 https://bou.org.uk/?p=77609 Fruit farms and forest fragments support distinct bird communities in the Brazilian Caatinga

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LINKED PAPER
Distinct bird communities in forests and fruit farms of Caatinga landscapes. Zielonka, N.B., Arellano, E., Crowther, L.P., Ferreira, V., Muñoz-Sáez, A., Oliveira-Rebouças, P., da Silva, F.O., Butler, S.J., Dicks, L.V..
2024. IBIS. DOI:10.1111/ibi.13311 VIEW

Grapes and mangoes may be a common sight in your fruit bowl, but have you ever wondered where the fruits come from? Well, let me take you on a journey to the ‘white forests’ of the Brazilian Caatinga – a diverse tropical dryland of thorny and semi-arid vegetation that appears dormant and white for most of the year, and bursts into life and greenery over the short rainy season. Despite the challenging conditions, over 2,000 species of plants and animals have made Caatinga their home, including dozens of endemic species not found anywhere else (da Silva et al. 2017). Over the past three decades, the region has also become home to irrigated fruit farms, which are always green, linear and heavily managed – a stark contrast to the forests of Caatinga (Figure 1). This rise in fruiticulture has been fuelled by the increasing demands for fruit exports to the Global North, and this has hugely benefitted regional development and poverty reduction. But how have the local bird communities responded to these habitat changes – are there winners or losers?

Figure 1. Example of a grape farm and the surrounding Caatinga forest in north-eastern Brazil during the wet season © Natalia Zielonka.

Agricultural expansion that leads to the loss of native habitats, and agricultural intensification which is associated with agrochemical use and habitat homogenisation, are key biodiversity threats and lead to losses in species richness and abundance (Newbold et al. 2016, Jaureguiberry et al. 2022). Beyond the direct losses, agricultural habitats can be characterised by altered communities, as some species are able to persist, or even benefit from the changes, whilst others decline in numbers and can ultimately disappear. Species’ responses are often explained by their ability to adapt to changes (such as habitat or food availability), and to deal with new or additional pressures (such as human disturbance), and so, broadly speaking, generalist species that thrive under a wider range of conditions persist at the expense of specialist species that require a more unique set of resources.

Loss of Birds

We surveyed birds across the agricultural landscapes of Caatinga to compare the communities in the fruit farms (table grape and mango) and forest patches. In short, bird abundance and diversity were significantly lower in the fruit farms compared to the forest patches: for every individual and species recorded within the fruit farms, there were 1.6 within the remnant Caatinga forest patches. Altogether, we recorded 78 different bird species across the landscapes, of which, 66 species (85%) used the forest patches, 48 (62%) used the grape farm and 28 (36%) used the mango farms.

Distinct Bird Communities

What is most interesting are the changes in the bird communities as we found fruit farms and Caatinga forest patches to be characterised by near-distinct assemblages, which were composed of different species (Figure 2). Some of these differences were expected – species with specialist diets were significantly less abundant in the fruit farms than in the Caatinga forests patches that they are adapted to. This included species that feed on insects (insectivorous species), which may struggle to find sufficient food within the fruit farms that heavily rely on agrochemicals and lack refugia for prey.  Such species are also frequently more sensitive to human disturbance and more likely to avoid crossing into the farms, even if they exist in the nearby forest patches. This is most concerning in the case of endemic species, such as the Caatinga Cacholote Pseudoseisura cristata and Campo Troupial Icterus jamacaii (Figure 3), which almost completely avoided the fruit farms in our study landscapes, and so, their persistence in the region may be threatened by continual agricultural growth

Figure 2. Non-metric multidimensional (NMDS) scaling of the abundance and composition of bird communities considering individual species across fruit farm and remnant Caatinga forest patches. Coloured points represent survey sites (n = 114) in each habitat patch, and the minimum convex polygons group these according to the survey habitat patch.

The winners across the fruit farm landscapes were species that can make use of a wide range of conditions and resources, such as omnivorous species (feed on a variety of foods), which made up 61% of all observed individuals. Unsurprisingly, 75% of the bird species we recorded are known to be able to adapt and thrive in human modified environments. The farm communities were dominated by a handful of species characterised by these traits, such as Picui Ground Dove Columbina picui, White-throated Seedeater Sporophila albogularis (endemic), Red-cowled Cardinal Paroaria dominicana (endemic), Common Waxbill Estrilda astrild (non-native) and House Sparrow Passer domesticus (non-native; Figure 3). Whilst this shows us that some endemic species are likely to persist, the list also includes two non-native species that were almost exclusively found within the farms, hinting at how continual expansion of fruit farms may change local bird assemblages.

Figure 3. Example bird species recorded across fruit farm and forest patches in the Caatinga, north-eastern Brazil © authors credited within the panel CC BY Wikimedia Commons.

Future Conservation

As far as fruit farm expansion across the Caatinga goes, our results suggest that its continuation may lead to the homogenisation of local bird communities. To help counteract this, retaining patches of the Caatinga forest and increasing habitat heterogeneity may help to support a higher number of bird (and non-bird) species and maintain regional connectivity (Salazar et al. 2021). More widely however, we argue that expanding the proportion of land under strict, legal protection away from agricultural areas may be key to the conservation of the highly biodiverse Caatinga biome. And finally, as consumers, we can become more mindful when reaching for tropical fruits and do our bit by supporting more sustainably produced food and avoiding waste.

References

Jaureguiberry, P., Titeux, N., Wiemers, M., Bowler, D.E., Coscieme, L., Golden, A.S., Guerra, C.A., Jacob, U., Takahashi, Y., Settele, J., Díaz, S., Molnár, Z., Purvis, A. 2022. The direct drivers of recent global anthropogenic biodiversity loss. Science Advances 8:45. VIEW

Newbold, T., Hudson, L.N., Arnell, A.P., Contu, S., de Palma, A., Ferrier, S., Hill, S.L.L., Hoskins, A.J., Lysenko, I., Phillips, H.R.P., Burton, V.J., Chng, C.W.T., Emerson, S., Gao, D., Pask-Hale, G., Hutton, J., Jung, M., Sanchez-Ortiz, K., Simmons, B.I., Whitmee, S., Zhang, H., Scharlemann, J.P.W., Purvis, A. 2016. Has land use pushed terrestrial biodiversity beyond the planetary boundary? A global assessment. Science 353:6296. VIEW

da Silva, J.M., Leal, I., Tabarelli, M. (eds). 2017. Caatinga: The Largest Tropical Dry Forest Region in South America. Springer International Publishing. VIEW

Salazar, A.A., Arellano, E.C., Muñoz-Sáez, A., Miranda, M.D., Oliveira da Silva, F., Zielonka, N.B., Crowther, L.P., Silva-Ferreira, V., Oliveira-Reboucas, P., Dicks, L.V. 2021. Restoration and conservation of priority areas of Caatinga’s semi-arid Forest remnants can support connectivity within an agricultural landscape. Land 10:550. VIEW

 

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What’s driving Lesser Kestrel declines despite conservation efforts? https://bou.org.uk/blog-afm-kestrel-declines-spain/ https://bou.org.uk/blog-afm-kestrel-declines-spain/#respond Thu, 22 Feb 2024 07:30:43 +0000 https://bou.org.uk/?p=77587 Reduced availability of prey and nesting sites may explain recent population declines

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LINKED PAPER
Causes of the recent decline of a Lesser Kestrel (Falco naumanni) population under an enhanced conservation scenario. Aparicio, J. M., Muñoz, A., Cordero, P. J., & Bonal, R. 2023. IBIS. DOI: 10.1111/ibi.13145. VIEW

Over the last century, Lesser Kestrel (Falco naumanni) populations have undergone dramatic changes. A sharp drop in numbers between the 1950s and 1990s led to the IUCN assessing the species as ‘Vulnerable’ in 1994, but population increases later resulted in a reclassification as ‘Least Concern’ from 2011 onwards (BirdLife International 2021). However, a recent census revealed a severe decline of 6% per year since 2012 in Spain, which hosts around 40% of the European breeding population (Bustamante et al. 2020). These recent declines occurred after the establishment of the European Union (EU) Natura 2000 network of protected areas, which was designed to safeguard species and habitats of biodiversity conservation interest, and are happening despite species-specific conservation measures such as captive breeding, reintroduction, and nestbox provision. Does this mean that these conservation actions aren’t working?

A recent study in Ibis examined Lesser Kestrel colonies in La Mancha, Spain, to identify any population changes, determine their causes, and establish if they are being addressed by current conservation actions.

Drivers of population declines
José Miguel Aparicio and colleagues collected data on colony size, land use, building conditions (i.e. nest-site availability), and density of Orthoptera (i.e. prey availability) from 12 La Mancha colonies in 2003 and 2021. They found that the study population had undergone a severe decline of 39.4% since 2003. As a population peak was estimated to have occurred in 2012, this indicates an annual decrease of 6% per year since the peak, matching previous findings for the whole of Spain (Bustamante et al. 2020).

Figure 1. Evolution of the Lesser Kestrel population between 1991 and 2021. Dots indicate population size relative to the maximum registered population. The solid line indicates the population estimate by regression fit to a third-degree polynomial function and the dashed line the 95% confidence interval.

The researchers concluded that reduced availability of large Orthoptera, the main food for Lesser Kestrel nestlings in the study area, is the main cause of recent kestrel population declines. This reduced prey availability seems to have caused by land use changes, in particular the loss of the Lesser Kestrel’s preferred foraging habitats which contained the highest densities of large Orthoptera: herbaceous crops and pasture lands (Assandri et al. 2022). Results also indicated that limited nest-site availability could be a threat to Lesser Kestrels, with a a significant loss of nesting habitat from 2003-2021 due to the deterioration or demolition of the old buildings in which Lesser Kestrels breed. During the study, the researchers discovered a dramatic increase of rabbit (Oryctolagus cuniculus) populations, with rabbit abundance having a negative effect on kestrel colony size. While this may have been due to the effects of overgrazing by rabbits on vegetation and Orthoptera abundance, the researchers suspected it was more probably due to the process of hyperpredation caused by the increased rabbit density attracting birds of prey which may opportunistically prey on kestrels (Smith & Quin 1996).

Figure 2. Mean (± se) density of large Orthoptera by land use in 2021.

Impact of conservation actions
While the inclusion of some areas within the Natura 2000 network appears to have slowed down land use changes and may have alleviated population declines, other actions such as the provision of artificial nestboxes had unclear effects, despite potentially being a way to mitigate the loss of nesting habitat. This may have been due to the population being limited by causes other than nest-site availability (Forero et al. 1996), or by nestboxes not being well designed or maintained. The nestbox entrance hole size was noted to be smaller than that of natural Lesser Kestrel nests, with a high level of occupation by Jackdaws (Corvus modedula). In fact, the increase in nestbox numbers was associated with an increase in the Jackdaw population, which could either compete with Lesser Kestrels or become allies against predators.

The researchers suggest future studies should examine whether the increase in nestboxes is facilitating the establishment of other species and analyse the consequences for Lesser Kestrels, as well as investigating the causal relationships behind the association between rabbit abundance and kestrel colony size.

References

Assandri, G., Cecere, J.G., Sarà, M., Catoni, C., De Pascalis, F., Morinay, J., Berlusconi, A., Cioccarelli, S., Mercogliano, A., Pazhera, A., Terras, A., Imperio, S., Morganti, M. & Rubolini, D. (2022). Context-dependent foraging habitat selection in a farmland raptor along an agricultural intensification gradient. Agriculture, Ecosystems & Environment 326: 107782. VIEW

BirdLife International (2021). Falco naumanni. The IUCN Red List of Threatened Species 2021: e.T22696357A205768513. VIEW

Bustamante, J., Molina, B. & del Moral, J.C. (2020). El cernícalo primilla en España, población reproductora en 2016–2018 y método de censo. Madrid: SEO/BirdLife. VIEW

Forero, M.G., Tella, J.L., Donfizar, J.A. & Hiraldo, F. (1996). Can interspecific competition and nest site availability explain the decrease of lesser kestrel Falco naumanni populations? Biological Conservation 78: 289–293. VIEW

Smith, A.P. & Quin, D.G. (1996). Patterns and causes of extinction and decline in Australian conilurine rodents. Biological Conservation 77: 243–267. VIEW

Image credits

Top right: Lesser Kestrel (Falco naumanni) | Sumeet Moghe | CC BY-SA 4.0 Wikimedia Commons

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‘The Boss’: factors explaining vocal activity and territorial behaviour https://bou.org.uk/blog-barrero-diego-duponts-lark/ https://bou.org.uk/blog-barrero-diego-duponts-lark/#respond Mon, 19 Feb 2024 07:30:50 +0000 https://bou.org.uk/?p=76761 Do intrasexual competition and resource availability modulate territorial displays in a steppe passerine?

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LINKED PAPER
Conspecific density and habitat quality drive the defence and vocal behaviour of a territorial passerine. Barrero, A., Gómez‐Catasús, J., Pérez‐Granados, C., Bustillo‐de la Rosa, D., Traba, J.
 2023. IBIS. DOI:10.1111/ibi.13295 VIEW

Territorial defence is described in a wide variety of taxa and occurs when an individual continuously defends an area against the presence or intrusion of conspecifics or heterospecifics. The “active territorial defence” hypothesis predicts that territorial individuals defend a fixed area to gain preferential access to resources such as food, mates and optimal breeding sites. Variation in the intensity of territorial defence and the sex targeted for exclusion may indicate the resource being competed for (i.e. food or mates), with this territorial defensive behaviour being expressed by one or more aggressive or visual displays and acoustic signals. Thus, territorial behaviour, along with other sexually driven traits such as body size, plumage colouring or body condition, may accurately reflect the relative quality of individuals, their hierarchical position and the quality of the territory they occupy. However, our current knowledge about birds’ territorial behaviour is limited to certain species.

Among those species for which its territorial behavior has never been studied before is the Dupont’s Lark Chersophilus duponti, a threatened steppe passerine. Shy, elusive, and very difficult to detect visually, it breeds from late February to late June (Barrero et al. 2023) and has been described as socially monogamous, although extra-pair copulations may occur. This species is distributed in territorial aggregations even on a small scale, where males maintain a territory throughout the year, increasing the intensity of territorial behaviour during the breeding season, favoured by a male-biased sex ratio (0.79). Their vocal activity consists mainly of territorial calls, songs and alarm calls emitted by males only.

In this study, we assessed whether the probability of Dupont’s Larks responding to a playback was associated to conspecific density and habitat quality. Furthermore, we assessed whether the intensity of male territorial response (i.e. vocal activity rate, type of vocalization employed) varied with habitat quality, conspecific density and close intrasexual competition, as well as with males’ body condition.

For this purpose, we conducted a single experiment simulating the intrusion of a foreign male in various locations with different population densities using a sound playback. In these locations, we measured habitat quality (assessed through vegetation indices positively correlated with food availability, Traba et al. 2022), intrasexual competition, and individuals’ physical condition. Additionally, we measured various movement and presence parameters (response probability, latency time, and minimum distance to the playback) and different singing performance parameters (vocal activity rate, singing rate, calling rate, alarm rate, and crowing rate) that could serve as honest signals of individual quality due to their direct energy cost.

Figure 1. Effect of ‘Kernel Density Estimator’ (KDE (a)), ‘Nearest-neighbour distance’ (b) and ‘BlueNDVI’ (c) on the response probability of Dupont’s Lark males in the study area. Variables on the x-axis are log-transformed. Mean (blue lines) and 95% BCI (grey surfaces) are depicted.

Dupont’s Lark males exhibited higher responsiveness in areas with a high density of males, both at the landscape (KDE: Fig. 1a) and at the local scale (nearest neighbor distance: Fig. 1b). In addition, males situated in lower-quality areas (i.e., lower BNDVI values), which aligned with higher individual density, exhibited greater responsiveness than males located in higher-quality territories but with lower densities at the landscape scale (Fig. 1c).

Secondly, when testing the intensity of Dupont’s Lark males’ response to a potential intruder, we observed different scenarios: 1) Dupont’s Lark males took longer to respond in areas with lower individual density (Fig. 2a), particularly as the breeding season progressed; 2) Males in higher-quality areas (i.e., higher BNDVI values) defended their territory by exhibiting a higher vocal activity rate (Fig. 2b) and a higher singing rate (Fig. 2c); 3) The singing rate was also higher in areas with lower male density at the landscape scale (Fig. 2d), but where distances to the nearest neighbors were shorter (Fig. 2e); 4) Males in lower-quality areas predominantly responded with alarms (Fig. 2f), especially in those areas with higher male density at the landscape scale, particularly at the beginning of the study period, but also with crowing (Fig. 2g); and 5) Surprisingly, the body condition of the males was not an important predictor of any of the behavioral variables.

Figure 2. Effect of ‘Kernel Density Estimator’ (KDE; a, d), ‘BlueNDVI’ (b, c, f, g) and ‘Nearest-neighbour distance’ (e) on the acoustic response variables of Dupont’s Lark males in the study area. Variables are log-transformed and standardized. Mean (blue lines) and 95% BCI (grey surfaces) are depicted.

In summary, our findings suggest that males living in territories with better quality of habitat also inhabit areas with lower conspecific density and defend their territory with greater intensity, emitting more complex songs and exhibiting a higher vocal activity rate. Conversely, males situated in lower-quality areas behave as floaters, responding quickly but cautiously to the simulated intrusion of a foreign male by emitting alarms and clucking, without displaying an intensive territorial defense. Despite its difficulty, future studies should try to incorporate information on the reproductive status of individuals to examine whether the intensity of territorial defense and physical condition are related to the reproductive status of the monitored birds.

References

Barrero, A., Gómez‐Catasús, J., Pérez‐Granados, C., Bustillo‐de la Rosa, D., Traba, J. 2023. Nest Features and Nesting Niche Segregation in Five Iberian Steppe Passerines. Ardeola 70:2. VIEW

Traba, J., Gómez‐Catasús, J., Barrero, A., Bustillo‐de la Rosa, D., Zurdo, J., Hervás, I., Pérez-Granados, C., García de la Morena, E.L., Santamaría, A., Reverter, M. 2022. Comparative assessment of satellite‐and drone‐based vegetation indices to predict arthropod biomass in shrub‐steppes. Ecological Applications 32:8. VIEW

Image credits

Top right: Male Dupont’s Lark singing © Adrián Barrero.

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Lost Birds https://bou.org.uk/blog-montgomerie-lost-birds/ https://bou.org.uk/blog-montgomerie-lost-birds/#respond Thu, 15 Feb 2024 07:30:34 +0000 https://bou.org.uk/?p=76634 Understanding vagrancy

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Birders love vagrants – birds that have wandered outside their normal breeding, migratory, or winter ranges to show up in a new place, often far from where they belong. What fun to be able to add a new species to one’s life, country, or patch list with a bird that may well be abundant where it normally lives but is now special. Birders are often obsessed with tracking down these vagrants – often at considerable expense (Moore 2013) – for the bragging rights.

Several reasons have been suggested to explain the existence of vagrants (Bozó & Csörgő 2024), each of them probably correct for a particular species. It has long been appreciated that most vagrants to North America and Europe come from the west, with the prevailing storms, or from the south, with migrants. But are they really becoming more and more common these days. Certainly, there would seem to be more reported every year from Alaska and the UK. This past autumn saw what appears to have been an unprecedented number of North American vagrants in the UK, including in November 2023 the first record of a Cape May Warbler in England on the Isles of Scilly.

The earliest treatises on birds and ornithology by Aldrovandi, Belon, Ray and others in the 17th and 18th centuries make no mention of what we would now call vagrants, as far as I can tell. This is not so surprising as there may have been fewer than 1000 people worldwide studying birds in those days, albeit more often with the gun than a pair of binoculars.

The Scottish parson-naturalist John Fleming [1785-1857] provides the first cataloguing of vagrants that I am aware of, in his History of British Animals (Fleming 1828). Fleming even mentions ‘occasional visitants’ in the title of his book, and distinguishes between “Periodical Visitants chiefly [that] belong to the class of Birds” and “Stragglers…irregular visitants…Driven from their native haunts to this country by some temporary calamity, the persecution of foes, or the fury of a storm” He also includes possibly the earliest record of a vagrant from North America, a Swallow-tailed Kite killed at Ballachulish in Scotland in 1772. Dr John Walker [1731-1803] had written this in his personal diary, called ‘Aversaria’ now archived the Special Collections Department of the University of Glasgow. This kite is a large and striking North American bird that would have stood out from the local avifauna of western Scotland.

Then, in his History of British Birds, William Yarrell [1784-1856] summarized 40 examples of vagrants of some 20 North American species that had been recorded in Europe. He notes that most were found in the UK, but very few in Germany, France, and The Netherlands, reflecting the presumed typical movement of vagrants from west to east (Yarrell 1845). Yarrell called the occurrence of such vagrants “an interesting problem, with difficult solution” (quoted in Gätke 1860) as he could not fathom how a small bird could possibly cross the broad, inhospitable expanse of the Atlantic Ocean.

Figure 1. Heinrich Gätke (Gätke 1895).

The fabulously hirsute Heinrich Gätke [1814-1897] took up that challenge and deduced that such ocean crossings would be physically possible based on his estimates of flight speeds, distance travelled, and the endurance of a migratory bird. Though he came to the right conclusion, his estimates of flight speeds and stamina were far off the mark. Gätke’s interest in vagrants was fuelled by encountering 10 species far from their normal ranges—2 from Africa and 4 each from North America and far eastern Asia—during the first 19 years that he lived on Heligoland. Heligoland is a small archipelago in the North Sea off the northwest coast of Gätke’s native Germany and was to become, in 1891, the site of a justly famous bird observatory established by Gätke.

The establishment of bird observatories and the more-ready availability of binoculars and cameras in the 1900s certainly resulted in more vagrants being documented. Thus, it seems very likely that the increased numbers of vagrants reported in recent decades is the result of the post-war boom in birdwatching and the ease of travel to remote locales. There are now reckoned to be about 45 million birders in North America and 3 million in the UK. But the numbers of vagrants does depend on factors like the weather, the climate and the available habitat, all of which are now changing at an alarming rate. Birders might be delighted at the resulting increase in rarities but any well documented increase in the number of birds that seem to have lost their way might be yet another warning sign about the uncertain future of our natural environment.

Figure 2. Heligoland (Gätke 1895).

Further Reading

Bozó, L., Csörgő, T. 2024. Causes of vagrancy of North Asian passerines in western Europe. IBIS 166. VIEW

Fleming, J. 1828. A History of British Animals, exhibiting the descriptive characters and systematical arrangement of the genera and species of quadrupeds, birds, reptiles, fishes, mollusca, and radiata of the United Kingdom, including the indigenous, extirpated, and extinct kinds, together with periodical and occasional visitants. Bell & Bradfute:Edinburgh pp.565.

Gätke. H. 1860. On the occurrence of American birds in Europe. Proceedings of the Zoological Society of London 26.

Gätke, H. 1895. Heligoland as an ornithological observatory: the result of fifty years’ experience [translated from the German by R. Rodenstock]. David Douglas:Edinburgh.

Moore, D. 2013. Birds: Coping with an Obsession. New Holland:London.

Yarell, W. 1845. A History of British Birds. John van Voorst:London

Image credits

Top right: Cape May Warbler | CC BY-SA 4.0 Rhododendrites Wikimedia Commons

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Black-eyed Birds https://bou.org.uk/blog-lane-gannet-avian-influenza/ https://bou.org.uk/blog-lane-gannet-avian-influenza/#respond Mon, 12 Feb 2024 07:30:36 +0000 https://bou.org.uk/?p=76623 A new way to monitor impact of avian influenza in Gannets?

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LINKED PAPER
High pathogenicity avian influenza (H5N1) in Northern Gannets (Morus bassanus): Global spread, clinical signs and demographic consequences. Lane, J.V., Jeglinski, J.W., Avery‐Gomm, S., Ballstaedt, E., Banyard, A.C., Barychka, T., Brown, I.H., Brugger, B., Burt, T.V., Careen, N., Castenschiold, J.H., Christensen-Dalsgaard, S., Clifford, S., Collins, S.M., Cunningham, E., Danielsen, J., Daunt, F., D’entremont, K., Doiron, P., Duffy, S., English, M.D., Falchieri, M., Giacinti, J., Gjerset, B., Granstad, S., Grémillet, D., Guillemette, M., Hallgrímsson, G.T., Hamer, K.C., Hammer, S., Harrison, K., Hart, J.D., Hatsell, C., Humpidge, R., James, J., Jenkinson, A., Jessopp, M., Jones, M., Lair, S., Lewis, T., Malinowska, A.A., McCluskie, A., McPhail, G., Moe, B., Montevecchi, W.A., Morgan, G., Nichol, C., Nisbet, C., Olsen, B., Provencher, J., Provost, P., Purdie, A.,Rail, J., Robertson, G., Seyer, Y., Sheddan, M., Soos, C., Stephens, N., Strøm, H., Svansson, V., Tierney, D., Tyler, G., Wade, T., Wanless, S., Ward, C., Wilhelm, S.I., Wischnewski, S., Wright, L.J., Zonfrillo, B., Matthiopoulos, J., Votier, S.C.
 2023. IBIS. DOI:10.1111/ibi.13275 VIEW

Bass Rock is the world’s largest Northern Gannet colony. It makes an assault on every sense – the visual spectacle, the noise, and of course the smell! Sitting just 2.5km off the coast of East Lothian, 30 miles east of Edinburgh, this Scottish island stands out like an ethereal beacon with a haze of tiny white specs just visible over the summit, returning and departing birds a constant presence overhead.

When our research team left the island for the last time in the summer of 2021, the colony was a bursting, thriving seabird city.  One year later, the Bass Rock colony was devastated by Avian Influenza.

Figure 1. Bass Rock: top – a busy and healthy colony in July 2021; bottom – devastated by HPAI in July 2022 © Jude Lane.

High Pathogenicity Avian Influenza Virus (HPAIV) – a novel virus in seabirds

Avian Influenza Viruses (AIVs) circulate naturally in bird populations. High Pathogenicity Avian Influenza virus (HPAIV) H5N1 was first detected on a domestic goose farm in Southern China in 1996. Since then, it has evolved and spread across Asia, Africa, the Middle East, and Europe causing significant outbreaks in a variety of bird populations (European Food Safety Authority et al. 2023). In the UK, the first detections of a new H5N1 virus, occurred over the winter period of 2020-21. The first incursion of this HPAIV into seabirds was detected when a large number of Great Skua, an already vulnerable species of conservation concern, were infected and died during the summer of 2021 (Banyard et al. 2022). In 2022, HPAIV was catapulted into the public consciousness in the UK due to the unprecedented impact it was having on wild birds. Thousands of seabirds were dying at their colonies and washing up on beaches around the coastline. One of the hardest hit species was the Gannet.

The challenge and global impact

Monitoring seabirds is always challenging as they tend to breed in remote and difficult to access locations. Gannets are certainly no exception. Working during a HPAIV outbreak increased the challenge due to the additional protocols needed to safeguard fieldworkers and to prevent spread of the virus within and between colonies and species. However, despite the challenges, seabird researchers did all they could to study the impacts on Gannets. We collated information from across the global network of research teams. This confirmed HPAIV outbreaks at 40 of the 53 Gannet colonies, spanning from North-East Canada to France to North-East Norway, between April and September 2022.

Figure 2. The timing of HPAIV outbreaks across the Gannet meta-population in 2022, based on the first date unusual mortalities in adults were observed. Affected colonies (n = 40) are indicated by circles, coloured by date. Colonies where information was unavailable (n = 12) are indicated by open diamonds. A) Geographical context; B) colonies in the west Atlantic; C) colonies in the east Atlantic. A filled diamond indicates Bjørnøya (Bj, Norway, the northernmost colony) where no signs of HPAIV were observed.

Immunity and reason for hope

Whilst it was clear that many thousands of Gannets were dying, questions quickly arose regarding whether there were any individuals in infected colonies that had avoided catching the virus, or that caught the virus but survived. Mortality rates of infected individuals of some species, such as chickens, is known to be very high but nothing was known about the susceptibility of Gannets.

Days after the virus was known to be present at Bass Rock, we started seeing Gannets with unusual iris colouring; ranging from mottled to completely black. Gannets normally have piercing pale blue/grey eyes, so the black eyes were very conspicuous and something no-one had seen before. The combination of birds with black eyes being seen for the first time during the first known outbreak of HPAIV, led us to suspect that the black iris colouring was linked to infection.

Figure 3. Gannets on the Bass Rock colony in 2022 with black flecking in their irises. The condition was variable between individuals from a) healthy, b and c) increasing degrees of black flecks in the iris d) completely black iris, and asymmetrical irises affected to e) greater and f) lesser extents. No pattern was detected in the asymmetry of black irises.

Benefiting from having a group of birds within the colony previously marked with uniquely coded leg rings, we could monitor the survival of black-eyed birds during and after the outbreak.  A symptomatic black-eyed bird was subsequently found dead in Denmark, whereas other black-eyed birds were seen alive and seemingly well at the colony throughout the summer. This was encouraging as it could mean that some individuals were able to survive infection.

Figure 4. Colour-ringed Gannet with unique identification code © Jude Lane.

Analysis of blood samples taken from Gannets with black and normal eyes confirmed our suspicion. Seventy eight percent of black-eyed birds had antibodies to H5N1 showing that development of black in the iris is highly likely to be linked to a previous HPAI infection. Antibody responses to HPAIVs are poorly understood in wild birds. We hope our work will continue to inform our understanding of this HPAIV subtype and how the Gannet population will respond to the 2022 and possible future outbreaks. If black eyes can be used for monitoring recovered and now immune individuals, this has important implications for population modelling. For example, understanding potential impacts of the virus on breeding productivity and longer-term survival.

Securing a future for seabirds

Seabirds are under massive pressure from climate change, lack of prey fish, entanglement in fishing gear, predation by non-native invasive species and developments along our coasts. The Seabirds Count 2015-2021 revealed revealed that almost half of species that regularly breed in Britain and Ireland have declined over the past 20 years (Burnell et al. 2023). This outbreak has highlighted HPAIV as an additional and major human-generated threat to seabirds.  We urgently need to implement actions for our vulnerable seabirds to ensure robust populations that are resilient to all the pressures we are placing on them.

Northern Gannets are currently classified as Least Concern for their conservation status by the IUCN. The UK Gannet population grew between 2015-2021 (Burnell et al. 2023). A number of the larger colonies such as Bass Rock and Grassholm, Wales are known to have suffered high mortality from the 2022 HPAIV outbreak, however it is still not know what the impact of the outbreak has been on the UK population. Even for such species that currently appear to be doing well, there should be no complacency in putting into place long-term monitoring, research, and response plans so that they can continue to thrive.

References

Banyard, A.C., Lean, F.Z.X., Robinson, C., Howie, F., Tyler, G., Nisbet, C., Seekings, J., Meyer, S., Whittard, E., Ashpitel, H.F. 2022. Detection of Highly Pathogenic Avian Influenza Virus H5N1 Clade 2.3.4.4b in Great Skuas: A Species of Conservation Concern in Great Britain. Viruses 14:212. VIEW

Burnell, D., Perkins, A.J., Newton, S.F., Bolton, M., Tierney, T.D., Dunn, T.E. 2023. Seabirds Count: A census of breeding seabirds in Britain and Ireland (2015-2021). Lynx Edicons ISBN: 9788416728602. VIEW

European Food Safety Authority, European Centre for Disease Prevention and Control, European Reference Laboratory for Avian Influenza, Adlhoch, C., Fusaro, A., Gonzales, J.L., Kuiken, T., Marangon, S., Niqueux, E., Staubach, C., Terregino, C.,  Aznar, I., Munoz Guajardo, I., Baldinelli, F. 2023. Scientific report: Avian influenza overview September– December 2022. European Food Safety Authority Journal 21:7786. VIEW

Image credits

Top right: The eyes of Gannets are usually pale blue-grey © Sam Hobson.

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Inspiration from the #AOC2023 https://bou.org.uk/blog-blackburn-aoc-2023/ Thu, 08 Feb 2024 07:30:11 +0000 https://bou.org.uk/?p=76620 Grace provides an account of her time at #AOC2023 presenting some of her research.

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I was recently able to attend the 2023 Australasian Ornithological Conference thanks to a BOU Member Conference Attendance Award. This year, over 400 ornithologists gathered in Brisbane to meet and talk all things birds. While I did attend the 2022 AOC online, and present work conducted during my masters, this was the first in-person AOC that I had been to. Being able to meet and talk to researchers from around Australia, as well as BirdLife representatives, was a fantastic experience and opportunity, and I really appreciate the BOU for helping to fund my attendance of this conference.

I presented work from one of my PhD chapters, investigating how the simultaneous occurrence of multiple anthropogenic stressors affects behaviour in Western Australian magpies. While presenting was a nerve-racking experience, as this was only the second in-person conference I had ever attended, I was really pleased with the experience, and received great feedback from people in the audience. I also received some fantastic and thoughtful questions that helped to stimulate ideas for future work in this area.

Given that my PhD is focused on the effects of anthropogenic noise, my favourite symposium to attend was the ‘Birds and transportation activities’ symposium. It was really interesting to hear about the work going on at airports to deter birds and reduce bird strikes, as well as learning about the effects of drone home delivery services on avian abundance. I was also able to chat with some of the speakers from this session afterward and talk about their work, which was a great networking opportunity and hopefully will lead to some collaborations in the future.

Figure 1. Grace Blackburn, Assoc/Prof Mandy Ridley, and Lizzie Speechley (left to right) at the 2023 AOC.

The organising committee for the 2023 AOC did an amazing job. There were fantastic plenaries, a good amount of talk sessions and workshops, great food, and free coffee – everything you need for a great conference. I am very grateful I was able to attend the 2023 AOC and came away from it with lots of inspiration for future work and collaborations with other amazing researchers and ornithologists around Australia.

The next AOC will be held in Perth in 2025 and is already being organised by a fabulous team of Western Australian researchers, including my PhD supervisor Mandy Ridley. I look forward to seeing even more ornithologists and researchers gather in Perth to discuss birds and science!

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