Meeting Abstract
Testosterone is thought to play a major role in the physiology and behavior of spring migration but questions remain. American Redstarts (S. ruticilla) treated with testosterone advance departure from their wintering grounds in the Neotropics. Yet various species castrated after winter solstice will fatten and express migratory restlessness in captivity. It is not known whether testosterone is essential for initiation of vernal migration in free-living White-crowned Sparrows (Z.l. gambelii). Thus, we tested the hypothesis that testosterone is necessary for a timely departure at the outset of vernal migration by chemically castrating male White-crowned Sparrows. We captured 12 adults (A) and 11 first years (F) birds near Davis, CA early April 2014 as they were finishing prealternate molt prior to premigratory fattening and migratory departure. Individuals were randomly assigned to either treatment or control group. Treatment birds (6 A and 6 F) received two flutamide (antiandrogen) and two 1,4,6-androstatriene-3,17-dione (ATD, aromatase inhibitor) implants after capture while controls (6 A and 5 F) received blank implants. Birds were then held for 48 hours in outdoor aviaries for observation then received a 0.7 g radio-transmitter before release. Each bird was located at least once every day after release until they disappeared from the area. We found that treatment did not delay departure (P>0.05); however, age influenced timing – adults departed significantly earlier than first year birds regardless of treatment (P<0.05). Contrary to the hypothesis, testosterone is not influencing initiation of migratory departure while suggesting age and possibly other factors are involved, the nature of which remain to be investigated.
