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PIT-tagging passerines – think twice prior to choosing the place

Short-term effects of PIT-tagging small birds

Krista N Oswald
Nelson Mandela University Department of Zoology, and
Rhodes University Department of Zoology and Entomology, South Africa
Anthony A Evlambiou
Nelson Mandela University Department of Zoology, and
Rhodes University Department of Zoology and Entomology, South Africa
Ângela M Ribeiro
Natural History Museum of Denmark, Denmark
Ben Smit
Nelson Mandela University Department of Zoology, and
Rhodes University Department of Zoology and Entomology, South Africa
Tag location and risk assessment for passive integrated transponder-tagging passerines. Krista N. Oswald, Anthony A. Evlambiou, Ângela M. Ribeiro & Ben Smit. 2018. IBIS. DOI: 10.1111/ibi.12558. VIEW

Being able to accurately record body temperature in individual birds is central to many fields of zoology, especially eco-physiology. In ornithology, the majority of pre-2000s (and occasionally later years) research analysing body temperature involved either insertion of a thermocouple into a birds’ cloaca, insertion of a thermocouple into the brainstem, or surgically implanting loggers/transmitter. Recently, researchers have almost universally moved to PIT-tags to obtain measurements.

Although the above mentioned move was prompted by multiple concerns over thermocouples including stress and possibly laceration, our concern was the preferred method of implantation (intra-peritoneal) may have been just as injurious for smaller passerines. Thus, we set out to test the influence of PIT-tag location in body temperature measurements as well as in bird’s fitness. Our study’s aim was two-fold:

  1. Compare body temperature recorded by PIT-tags (Fig. 1) inserted intra-peritoneally (into the abdomen) with those inserted sub-cutaneously inter-scapulae. Our sample included 21 Zebra Finches (Taeniopygia guttata; “Finches”) alternately given intra-peritoneal (six females, five males) or sub-cutaneous (five females, five males) PIT-tags. Finches were placed in a respirometry chamber, with body temperatures recorded at three air temperatures (~ 5, 30, and 40 °C) for between 30 – 60 minutes each. We found no significant difference in body temperatures recorded between intra-peritoneal and inter-scapulae insertion at any temperature treatment. We note that two females with tags inserted intra-peritoneally died leaving final intra-peritoneal sample size as five females, five males. These regrettable occurrences helped confirm the high risk of inserting PIT-tags intra-peritoneally.
  2. Figure 1 PIT-tags are 12 mm long with 2.1 mm diameter with unique alpha-numeric ID codes. They are triggered electromagnetically when a PIT-tag reader is nearby, eliminating the need for a battery. They allow for precise temperatures to be recorded, and are inserted using an open-tipped 6 gauge implanter needle

  3. Short-term injury assessment of PIT-tags inserted intra-peritoneally in three passerines with different mass. Finches represented our smallest birds (~15 g), Karoo scrub-robins (Cercotrichas coryphaeus; “Scrub-robins”) [Figure 2] represented our medium-sized birds (~ 20 g), and Cape Rockjumpers (Chaetops frenatus; “Rockjumpers”) represented our large birds (~55 g). Scrub-robins and Rockjumpers were caught and PIT-tags implanted for seasonal physiological studies (Oswald et al. 2018) that occurred from July 2015 through July 2016. Sample sizes included the 21 Finches mentioned above (11 intra-peritoneal, 10 sub-cutaneous), 73 Scrub-robins (all intra-peritoneal) and 35 Rockjumpers (all intra-peritoneal). Twenty Scrub-robins were euthanized and necropsied as part of the above-mentioned separate study by AMR, allowing for post-mortem analysis.
  4. Figure 2 A researcher holds a Karoo Scrub-robin (Cercotrichas coryphaeus) in hand after processing measurements. Karoo scrub-robins represented our medium-sized birds (~20 g) for the portion of our study that dealt with comparing injury from PIT-tag insertion from different masses of birds

Our results revealed that location of PIT-tags negatively affected small bird’s fitness, while having less effect on medium-sized birds, and no recorded effect on large-sized birds.

In the small Finches, we found 18.2 % injury in intra-peritoneal PIT-tagged individuals and no injury when PIT-tags were inserted sub-cutaneously. On the contrary, only 2.7 % of Scrub-robins were injured, with no injury observed in Rockjumpers. Somewhat worryingly, two of the Scrub-robins, apparently doing well (no behavioural change and eating well while in captivity) had liver damage that was only discovered after post-mortem necropsy. Thus, we hypothesize further injury may have occurred after the birds’ release. For Rockjumpers, ad hoc observations over the year after PIT-tag implantation allowed us to have a rough estimate of longer term effects in our largest birds. Although not all territories were revisited, forays into the territories of a possible 27 tagged individuals saw 20 re-sighted and active during the next breeding season (post-August 2016; Fig. 3).

Figure 3 The number of individuals given PIT-tags either intra-peritoneally (IP) or sub-cutaneously inter- scapulae (SC) for our three birds (Finches, Scrub-robins, and Rockjumpers), along with individuals experiencing injury. Injury was found only in our smaller two mass categories, and only for the intra-peritoneal method of insertion. The inset diagram shows the relative size of the PIT-tag for each of our bird mass categories

Given the unfortunate events with Finches and the injuries in Scrub-robins and the evidence that placement of tempearture-sensing tags subcutaneously in the inter-scapular area had no effect on body temperature measurments , it is our opinion that researchers preferentially choose sub-cutaneous inter-scapulae PIT-tag insertion over intra-peritoneal when studying smaller passerines in an effort to minimize potential negative effects (Fig. 4).

Figure 4 A male Cape Rockjumper (Chaetops frenatus) minutes after PIT-tag insertion sub-cutaneously inter-scapulae is held by a volunteer. Although we found the larger mass of Cape Rockjumpers resulted in no visible injuries to birds, we suggest that sub-cutaneous method of insertion be preferentially chosen if possible



Oswald, K.N., Lee, A.T.K., Smit, B. 2018. Seasonal physiological responses to heat in an alpine range-restricted bird: the Cape Rockjumper. bioRxiv DOI: 10.1101/248070. VIEW

About the authors

Krista N Oswald works as a postgraduate student at Rhodes University in the Department of Zoology and Entomology. Her work uses the Cape Rockjumper (Chaetops frenatus) as an indicator species for how range-restricted, ground-nesting birds with constricting habitats, and decreasing populations respond to increasing temperatures. Krista’s current project: ‘Vulnerability of a Fynbos-endemic bird to climate warming: past and present responses to high temperatures’ looks at behaviour, reproduction, and genetics to try and isolate causal evidence for declining Rockjumper populations.
View Krista’s website
View Krista’s full profile on ResearchGate
Follow Krista on Twitter @Krista_Natasha
Anthony A Evlambiou is a Masters student at Rhodes University in the Department of Zoology and Entomology. His work is on the Acontias genus of burrowing legless skinks with his current project titled ‘Body morphologies of Acontias legless skinks are linked with biome characteristics in South Africa’ looks at whether isolated populations have become separate species due to their low dispersal ability. As all the species of Acontias have very similar appearances new ways of identifying species are also being looked into. Work is also being done to link head-shape to the environment in which the creatures are found.
View Anthony’s full profile on ResearchGate
Ângela M Ribeiro was a Marie Curie fellow, post-doc, at Natural History Museum of Denmark. She is an evolutionary biologist broadly interested in understanding the environment-organism linkages at different scales (from behaviour to local adaptation) with a keen interest in arid-zones.
View Angela’s full profile on ResearchGate
Ben Smit was a former lecturer and researcher in animal physiology at Nelson Mandela University. Currently, he is a senior lecturer at Rhodes University studying ecological and evolutionary physiology. His main interest relates to the role of thermal physiology in driving local adaptation, and answers these questions by integrating animal behavioural ecology, reproductive ecology and evolutionary history with comparative physiology.
View Ben’s full profile on ResearchGate

Image credit

Top right: Cape Rockjumpers (Chaetops frenatus; male pictured) are a near-threatened endemic bird of the South African Cape Fold Mountains © Krista N Oswald

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