Tag location and risk assessment for passive integrated transponder-tagging passerines

Understanding changes in body temperature is central to several fields in biology, but determining these changes accurately without harming or restraining individuals can be challenging, particularly for small species. We tested first whether body temperature readings differed between passive integrated transponder (PIT) tags injected subcutaneously inter-scapulae (i.e. solely through the skin) and intra-peritoneally (through the skin and abdominal muscle wall) and, secondly, whether intra-peritoneal tag injuries differed among three weight classes of passerines. We found no significant difference in body temperature readings between subcutaneous inter-scapulae and intra-peritoneal PIT-tags, and observed that the intra-peritoneal injection of PIT-tags may cause adverse effects among smaller (<25 g) birds. Our findings suggest a reduced gradient between core and peripheral body temperature in small species, which to the best of our knowledge has not yet been quantified. We further show that the risk of detrimental injury was greatest in small species, and thus recommend implanting PIT-tags subcutaneously between the scapulae for smaller birds.