1 3 J Comp Physiol A DOI 10.1007/s00359-015-1050-3 ORIGINAL PAPER Sex steroid profiles and pair-maintenance behavior of captive wild-caught zebra finches (Taeniopygia guttata) Nora H. Prior 2,9 · Kang Nian Yap 1 · Hans H. Adomat 5 · Mark C. Mainwaring 6 · H. Bobby Fokidis 1,5,7 · Emma S. Guns 5 · Katherine L. Buchanan 8 · Simon C. Griffith 6 · Kiran K. Soma 1,2,3,4 Received: 7 April 2015 / Revised: 12 October 2015 / Accepted: 29 October 2015 © Springer-Verlag Berlin Heidelberg 2015 significantly different between the sexes (female > male). Circulating pregnenolone levels were high in both sexes, suggesting that pregnenolone might serve as a circula- ting prohormone for local steroid synthesis in zebra finches. Furthermore, circulating testosterone levels were extremely low in both sexes. Additionally, we found no correlations between circulating steroid levels and pair- maintenance behavior. Taken together, our data raise sev- eral interesting questions about the neuroendocrinology of zebra finches. Keywords Affiliation · Pair bond · Songbird · Steroid profiling · Opportunistic breeder Introduction Monogamy occurs across a wide range of species, includ- ing primates, rodents, birds, reptiles and fish (Reichard and Boesch 2003). Importantly, there is considerable variation within monogamous mating systems (Black 1996; Reich- ard and Boesch 2003). Pair bonds can be transient (last- ing one breeding cycle) or life-long (Reichard and Boesch 2003). For species that form transient pair bonds, individu- als repeatedly invest time and effort in courtship and pair- bond formation; however, it is unclear whether significant investment is needed to maintain these short-term bonds. In sharp contrast, for species that form life-long pair bonds, it is arguable that the ability to maintain a pair bond is equal to or more important than the ability to form the initial bond. While the importance of pair bonds has long been recognized in ethology (Silcox and Evans 1982; Beletsky 1983; Evans and Poole 1984; Black 1996), relatively little is known about the neuroendocrine regulation of pair-bond maintenance. Abstract Here, we studied the life-long monogamous zebra finch, to examine the relationship between circulating sex steroid profiles and pair-maintenance behavior in pairs of wild-caught zebra finches (paired in the laboratory for >1 month). We used liquid chromatography–tandem mass spectrometry to examine a total of eight androgens and progestins [pregnenolone, progesterone, dehydroe- piandrosterone (DHEA), androstenediol, pregnan-3,17- diol-20-one, androsterone, androstanediol, and testos- terone]. In the plasma, only pregnenolone, progesterone, DHEA, and testosterone were above the limit of quanti- fication. Sex steroid profiles were similar between males and females, with only circulating progesterone levels * Nora H. Prior nhprior@zoology.ubc.ca 1 Psychology Department, University of British Columbia, Vancouver, BC, Canada 2 Zoology Department, University of British Columbia, Vancouver, BC, Canada 3 Graduate Program in Neuroscience, University of British Columbia, Vancouver, BC, Canada 4 Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, BC, Canada 5 The Prostate Centre at Vancouver General Hospital, Vancouver, BC, Canada 6 Department of Biological Sciences, Macquarie University, North Ryde, NSW, Australia 7 Department of Biology, Rollins College, Winter Park, FL, USA 8 School of Life and Environmental Sciences, Deakin University, Geelong, VIC, Australia 9 Present Address: Université de Lyon/Saint-Etienne, Neuro- PSI/ENES CNRS UMR 9197, Saint-Etienne, France