Meeting Abstract
P1.149 Tuesday, Jan. 4 Testosterone and aggression in free-ranging male Cassin’s Sparrows, Poecile cassinii DEVICHE, Pierre J*; DAVIES, Scott; FOKIDIS, Bobby; HURLEY, Laura; Arizona State University; Arizona State University; Arizona State University; Arizona State University deviche@asu.edu
According to the “challenge hypothesis”, male birds in breeding condition increase testosterone (T) secretion during periods of enhanced aggression such as following simulated territorial intrusion (STI), and this increase may facilitate behavioral responses to a subsequent or continuing challenge. We investigated this hypothesis in free-ranging male Cassin’s Sparrows, Poecile cassinii, at the beginning of their breeding season in southeast Colorado, USA. During a 10 min-long STI (conspecific song playback), sparrows increased their aggressive behavior as indicated by decreased latency to approach the song playback speaker, increased time spent close to the speaker, and decreased skylarking flight rate. The behavioral response to STI was not accompanied by altered plasma T: plasma T did not differ in males exposed to a short (average: 4 min) vs. long (average: 36 min) STI and it was not correlated with the duration of STI in either experimental group. Further, birds exposed to STI for the first time showed the same behavioral response as males having experienced the same STI 30 min earlier, indicating no persistent behavioral effect of exposure to initial STI. We hypothesized that the lack of plasma T increase in response to STI was due to incapacity of the testes to increase their androgen secretion. This was not supported by the observation that an i.v. injection either of gonadotropin-releasing hormone (0.025 mg/kg) or of purified ovine luteinizing hormone (1 mg/kg) increased plasma T within 20 min of administration and the increase was similar in males exposed to short or long duration STI. This data provide no evidence that T in breeding condition males regulates short-term changes in antagonistic behavior in response to STI. Support: CO Field Ornithologists.
