Yolk Androgens and Development in American Kestrel Nestlings

Maternally derived yolk androgens affect many aspects of phenotypic development. To explore this phenomenon I injected clutches of American kestrels (Falco sparverius) with one of three different dosages of testosterone + androstenedione or with vehicle. Morphological measurements taken from nestlings 26 days after hatching showed no significant treatment effect. In 2007, nestlings with more yolk androgens had lower hatching mass and higher hematocrit levels 15 days after hatching than nestlings with less yolk androgens, but the effects disappeared by day 26. In 2008, there were no effects of androgens on mass or hematocrit. Because the results were not consistent between years, and because field year had a significant effect on many morphological and blood measurements, androgens may be linked to the environmental conditions. Over two field seasons, control clutches and clutches given the largest dosage of androgens had the highest number of nestlings hatch and fledge. The survival rate from a clutch was affected differently depending on the amount of exogenous androgens injected into the eggs. A study by Sockman and Schwabl (2000) supports the anomaly of lowered survival as a function of exogenous androgens, but their nestlings died mostly after hatching and the kestrels in my study died before hatching.