Parental testosterone and estradiol concentrations in the early nestling period correlate with the age-dependent breeding performance in Tawny Owls Strix aluco

Abstract

Steroid hormones, which have not previously been examined in nocturnal raptors, were studied in male and female Tawny Owls (Strix aluco). The role of sex steroids during their peak concentrations – the territorial period and egg formation – has recently been documented. During post-hatching periods, the breeding success might negatively correlate with steroid levels. To test this idea, we analysed testosterone and estradiol concentrations during the early nestling period of Tawny Owl, and linked the hormone levels to parental age and breeding performance. We found that females older than two years laid more eggs with higher hatching success than did younger females, and pairs with males older than two years achieved higher fledging success than did pairs with younger males. Testosterone levels in males and testosterone and estradiol levels in females were higher in threeyears old than in younger individuals. In females, estradiol and testosterone concentrations positively correlated with the number of eggs laid and their hatching success. In males, testosterone concentrations positively correlated with fledging success. These findings suggest that parents with higher hormone levels in early nestling period are of higher quality with respect to breeding performance.