Meeting Abstract

P3.99  Saturday, Jan. 5  Breeding season changes of plasma testosterone level in the Eastern Kingbird REDMOND, L.J.*; MURPHY, M.T.; COOPER, N.W.; O’REILLY, K.M.; Portland State University; Portland State University; Portland State University; University of Portland luk916@hotmail.com

We quantified behavioral and breeding season relationships of testosterone of Eastern Kingbirds (Tyrannus tyrannus) in southeastern Oregon from 2005 to 2007. Kingbirds were captured with mist nests either passively or with playback and blood samples were taken for testosterone assays. Despite the use of playback during the capture of many individuals, we found no influence of capture method or time to capture on plasma testosterone levels. Testosterone concentrations ranged from 0.004 to 1.509 ng/mL and fell within the range reported for other songbirds. Additionally, many samples had undetectable levels of testosterone the majority of which were collected later in the year. Therefore, we tested for, and found a significant inverse relationship between date in the season and testosterone level. We also found a significant, negative relationship between day of the nest cycle and testosterone. Testosterone was highest before and during egg laying and was low throughout the remainder of the nest cycle. To the best of our knowledge this is the first study to document breeding season testosterone profiles and evaluate behavioral and breeding season correlations of this hormone in the family Tyrannidae.