Circulating sex-steroid dynamics in relation to nest building in the zebra finch, Taeniopygia guttata

Background: Although circulating sex steroids seem to be necessary for nest building in birds (e.g., Martinez-Vargas, 1974; Walters & Harding, 1988), it is unclear whether these hormones only trigger the behaviour, or if they are needed throughout the building period. Using the zebra finch, a species in which the male is the primary builder, we began to address this question by providing the first detailed report of circulating steroid dynamics in breeding pairs, focussing especially on the nest-building period.
Methods: Blood was collected from two groups of adult male and female zebra finches (n=16 pairs/group) at three of the following timepoints: (1) during single-sex pair housing (baseline), (2) after 48 h of male-female pair-housing (courtship), (3) on day 2 of nest building, and (4) 48 hours after nest building was stopped (we removed the nest). We then measured testosterone (radioimmunoassay; male samples) or 17β-oestradiol (enzyme immunoassay; female samples) levels in samples of the birds’ plasma.
Results: Circulating testosterone levels were high in most males throughout courtship and nest building, with levels dropping only after nest building had stopped. It also appears that individual circulating testosterone levels during courtship might predict males’ readiness to build. In contrast, 17β-oestradiol levels in females were largely unaffected by the nest-building activities per se, as they showed an initial increase before reaching a plateau.
Conclusions: Taken together, our data indicate that high circulating testosterone levels are associated with nest building by male zebra finches. As central aromatisation of testosterone into 17β-oestradiol is likely to be the mechanism through which testosterone initiates and supports male nest building (Walters & Harding, 1988), our results pave the way for further studies to investigate this system.