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Constrained to roam by your breeding neighbour

What influences the home range of tropical Red-capped Larks in a habitat devoid of any seasonality?

 
Joseph Mwangi
University of Groningen, Netherlands
National Museums of Kenya, Kenya
Natural Africa Concern, Kenya
 
 
LINKED PAPER
Home ranges of tropical Red-capped Larks are influenced by breeding rather than vegetation, rainfall or invertebrate availability. Mwangi, J., Klaassen, R.H.G., Muchai, M. & Tieleman, B.I. 2019. IBIS. DOI: 10.1111/ibi.12716. VIEW

For most animals, humans included, planning in time is essential. But for effective planning, knowing what to expect next is critical. If you live in high latitude areas, say, for example, Europe, while enjoying the warm climate of summer, you prepare for the autumn when all the trees shed leaves, and the birds reduce their singing while some prepare to migrate. Autumn gives way to winter when you tuck yourself indoors or look forward to that skiing trip when the snow falls. To complete the cycle, at the end of winter season, spring rushes in and all the life comes back, flowers start to blossom, birdsong is everywhere and you can’t wait to put your heavy jacket away and replace it with light outing wear. But for low latitude residents, these pronounced and clearly defined seasons are not always vivid, although in some areas there are clear wet and dry seasons, mostly dependent on altitude. As you get near the equator, day length is constant year-round and winter, summer, autumn and spring are nothing but strange terms, while in the advent of climate change, even previously seasonal environments areas are now becoming non-seasonal.

Relating this to my own personal experience as a budding ecologist from Kenya, who grew up near the slopes of Aberdare Mountains, where everything is green year round. The one intriguing experience I constantly recall at the start of my PhD study in the Netherlands was parking our car outside with everything grey and coming out three hours later after a bowling game, only to find everywhere covered in snow and all white. I almost thought I had been teleported to a different universe.

Similar to humans, for most species of animals, environmental cues allow them to predict future conditions like food availability, the best time to breed, when predation levels are low, et cetera, et cetera. But how can equatorial afro-tropical birds adjust their behaviour when the environment is constantly changing in an unpredictable stochastic way?

This forms the basis of my PhD thesis, entitled “Coping with uncertainty: adapting to stochasticity in an unpredictable tropical environment”, in which I examine the interactions and influences of the unpredictable weather and resource variation experienced by Red-capped Larks Calandrella cinerea in tropical equatorial habitats and how it influences their breeding success, home-range, body condition and immune function. The stochastic nature of near-equatorial tropical areas with occurrence of year-round breeding provides “natural experiments”, offering an opportunity to tease apart effects of environmental factors and life history stages in natural populations in influencing behaviour and physiological condition of birds.

This contributes a new dimension to current life-history theory predominantly advanced by studies carried out in the highly seasonal and predictable north temperate areas, by teasing apart and examining separately the effects of weather, food and social interactions on survival and reproductive fitness of animals. This is an important step because thus far the majority of studies focused on temperate zone environments where seasonal changes of weather and associated resources are highly correlated and synchronized with energetically intensive life history events such as breeding and moulting. In such seasonal temperate zone environments, it is impossible to tease apart independent effects of different environmental factors on nest survival, behaviour, body condition and immune function independent of each other.

Figure 1 A composite figure of the study system showing the country where the study was carried out (top right), the field site (top centre), and below starting from the left: weather station, pitfall invertebrate sampling, nest type, mist net capture method and biometric measurements © J Mwangi

Our study species the Red-capped Lark is a small gregarious bird found in short-grass and bare-ground habitats widely distributed across Africa (Zimmerman et al. 2005). Males and females form pairs during breeding but interact in mixed-sex flocks when not breeding. Pairs build ground-level open-cup nests and typically lay two eggs per clutch. Clutch size is usually two eggs but 1–3 egg clutches occur occasionally (Ndithia et al. 2017). With breeding and non-breeding co-occurring year round, and breeding occurring without direct associations with rainfall, temperature, and invertebrate biomass, we exploited the opportunity to tease apart effects of breeding, food availability and weather conditions on home range and space use of Red-capped Larks.

Figure 2 Naomi Wanjiku, one of the research assistants hand tracking radio-marked Red-capped larks by homing on foot using handheld radio receivers (SIKA Radio Tracking Receiver, Biotrack Limited, Wareham, UK) attached to a 3-element flexible antenna (Yagi 173 MHz, Biotrack Limited) © J Mwangi

Home range in Red-capped Larks was not related to food availability or weather conditions, but rather decreased with an increase in nesting intensity at the population level. This result applied to both the combined composite home ranges of breeding and non-breeding birds and to the home ranges of non-breeding birds only. For brooding birds and secondly birds with altricial young, such as the Red-capped Larks, home range of breeding birds may have been influenced by nest attendance during incubation and maintaining a continuous presence at the nest to minimize the risk of nest predation (Rothenbach and Kelly 2012), while chick provisioning also constrains movement to areas closer to the nest (Morganti et al. 2017). Red-capped Larks during breeding defend their nest sites against intrusion by conspecifics. Territoriality by breeding birds may explain the decrease of non-breeding birds with an increase in nesting intensity as territoriality reduces the area available to non-breeding birds. Consequently, exclusion from some areas creates patchiness in areas accessible for non-breeding birds to exploit, restricting them to smaller areas that are not defended by the breeding pairs.

Video A Red-capped Lark tagged with a radio-transmitter © J Mwangi

Our study underlines the relevance of conducting more studies in aseasonal tropical areas in order to disentangle effects of weather, food availability and breeding that vary in parallel, but that peak simultaneously in most seasonal areas.

 

References

Morganti, M., Assandri, G., Aguirre, J. I., Ramirez, Á., Caffi, M. & Pulido, F. 2017. How residents behave: home range flexibility and dominance over migrants in a Mediterranean passerine. Anim. Behav. 123: 293–304. VIEW
 
Ndithia, H.K., Matson, K.D., Versteegh, M.A., Muchai, M. & Tieleman, B.I. 2017. Year-round breeding equatorial Larks from three climatically-distinct populations do not use rainfall, temperature or invertebrate biomass to time reproduction. PLoS ONE 12: 1–18. VIEW
 
Rothenbach, C.A. & Kelly, J.P. 2012. The parental dilemma under variable predation pressure: Adaptive variation in nest attendance by Great Egrets. The Condor 114: 90–99. VIEW
 
Zimmerman, D.A., Turner, D.A. & Pearson, D.J. 2005. Birds of Kenya and Northern Tanzania. London: Helm.

 

About the author

Joseph Mwangi is a conservationist and an early career researcher based at the National Museums of Kenya. He is also a founder member of Natural Africa Concern, an NGO that aims to communicate scientific information on matters of natural history so as to empower the Kenyan society with the knowledge and feeling of connection with nature. He is currently finalizing a PhD. at the Groningen Institute for Evolutionary Life Sciences, Groningen University, Netherlands. His PhD study is funded by the Netherlands Fellowship Programme and supervised by Prof Irene Tieleman.
 
View Mwangi’s full profile on ResearchGate
 
Follow Mwangi on Twitter @imwangi3
 

Image credits

Top right: Red-capped Lark Calandrella cinerea ©Joseph Mwangi
 

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