Role of Testosterone in Stimulating Seasonal Changes in a Potential Avian Chemosignal Danielle J. Whittaker & Helena A. Soini & Nicole M. Gerlach & Amanda L. Posto & Milos V. Novotny & Ellen D. Ketterson Received: 10 August 2011 /Revised: 21 November 2011 /Accepted: 8 December 2011 /Published online: 16 December 2011 # Springer Science+Business Media, LLC 2011 Abstract Songbird preen oil contains volatile and semi- volatile compounds that may contain information about species, sex, individual identity, and season. We examined the relationship between testosterone (T) and the amounts of preen oil volatile and semivolatile compounds in wild and captive dark-eyed juncos (Junco hyemalis). In wild males and females, we observed an increase in volatile compound rela- tive concentration early in the breeding season. This increase mirrored previously described seasonal elevation in T levels in wild males and females, suggesting a positive relationship between hormone levels and preen gland secretions, and a possible role for these secretions in signaling receptivity. In females, the greatest relative concentrations of most com- pounds were observed close to egg laying, a time when steroid hormones are high and also the only time that females respond to an injection of gonadotropin-releasing hormone with a short-term increase in T. In a study of captive juncos held on short days, we asked whether the seasonal increases observed in the wild could be induced with experimental elevation of T alone. We found that exogenous T stimulated the production of some volatile compounds in non-breeding individuals of both sexes. However, of the 15 compounds known to increase during the breeding season, only four showed an increase in relative concentration in birds that received T implants. Our results suggest that testosterone levels likely interact with other seasonally induced physiological changes to affect volatile compound amounts in preen oil. Key Words Testosterone . Chemical communication . Chemical signals . Birds . Dark-eyed junco . Passerine . Steroid hormones . Preen gland Introduction Many species of vertebrates, including birds, produce chem- ical signals that may play an important role in social and reproductive behavior (Wyatt, 2003). The use of chemical communication by birds was doubted until recent years, when several studies began to decode information contained in these chemosignals (e.g., Mardon et al., 2010; Whittaker et al., 2010; Shaw et al., 2011), and provided evidence of the ability of birds to detect these chemicals (Bonadonna and Mardon, 2010; Whittaker et al., 2011) and a role of these chemicals in social and reproductive behavior (reviewed in Balthazart and Taziaux, 2009). In most species of birds studied to date, compounds that may play a role in chemical signaling are present in preen oil secreted from the uropygial, or preen, gland (Bonadonna et al., 2007; Soini et al., 2007). Birds spread this oil over feathers while preening, where it functions to protect the feathers from exposure to the environment, enhance insulation, and lower ectoparasite load (Jacob and Ziswiler, 1982). The volatile and semivolatile compounds in preen oil also contribute an odor to a bird, which varies qualitatively among species (Mardon et al., 2010), and D. J. Whittaker (*) BEACON Center for the Study of Evolution in Action, Michigan State University, 1441 Biomedical and Physical Sciences Building, East Lansing, MI 48824, USA e-mail: djwhitta@msu.edu D. J. Whittaker : N. M. Gerlach : E. D. Ketterson Department of Biology, Indiana University, 1001 E. Third Street, Bloomington, IN 47405, USA H. A. Soini : A. L. Posto : M. V. Novotny Institute for Pheromone Research and Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, IN 47405, USA J Chem Ecol (2011) 37:1349–1357 DOI 10.1007/s10886-011-0050-1