Meeting Abstract
36.3 Tuesday, Jan. 5 Living on the edge: does proximity to a geographical range boundary influence physiology in tropical song wrens (Cyphorhinus phaeocephalus)? BUSCH, D. S.*; ROBINSON, T. R.; ROBINSON, W. D.; WINGFIELD, J. C.; NOAA – Northwest Fisheries Science Center; Oregon State Univ.; Oregon State Univ.; Univ. of California, Davis shallinbusch@gmail.com
A species’ geographic range can be limited by a variety of biotic and abiotic factors. We studied the physiology of the song wren (Cyphorhinus phaeocephalus) along a rainfall-induced habitat gradient across the Isthmus of Panama, searching for a physiological signature of the species’ range edge. We measured body condition, hematocrit (% packed red blood cells in a given blood sample), and corticosterone levels (CORT, a steroid hormone that regulates the availability of energy and the stress response) in males and females. To lure our study subjects into mistnets for capture, we used recorded conspecific song (playbacks). We found that birds living in drier habitat near the range edge were significantly more likely to have abnormally low hematocrit scores. In one of our four PATH models, baseline CORT levels were negatively associated with rainfall, indicating potential energetic challenge or possibly chronic stress in some individuals. Body condition was positively correlated with rainfall; birds with the poorest body condition lived at the dry end of the gradient. Birds with better body condition and low baseline CORT levels were captured more quickly and, thus, exposed to conspecific playback for a shorter duration. Stress-induced CORT levels correlated significantly with sex only, being higher in females. Our results indicate a link among an environmental gradient and baseline CORT levels, body condition, response to playback, and hematocrit. Given the nature of the direct and indirect relationships in our data, we advocate the need for integrative studies that consider abiotic, behavioral, and physiological variables to better understand factors influencing the distribution of birds.
