Meeting Abstract
Early breeding individuals are often able to produce the most offspring; however, birds are unable to invest the energy to be fully prepared to breed when they are migrating long distances in the spring. Individuals wait until they arrive at the breeding ground to enter the final stages of reproductive preparation, but migration distance may be an important factor in determining when birds begin activating their reproductive systems. Previous studies have focused on males and monogamous species to investigate the relationship between migratory distance and reproduction. We propose that red-winged blackbirds (Agelaius phoeniceus), a polygynous species, are an ideal subject to study this relationship because it is advantageous to be the first female breeding on a territory. The first female typically gets the best nesting location and more parental investment from the male. We captured individuals upon arrival to the breeding ground and obtained a blood and claw sample from both males and females. Females were injected with GnRH to measure their maximum production of the sex steroid hormone testosterone as an estimate of the pituitary and ovarian status. Stable isotopes of hydrogen obtained from the claw samples provide an estimate of each bird’s overwinter location. Our study will explore whether migration distance, estimated using stable isotopes, plays a role in the activity or responsiveness of the reproductive endocrine axis upon arrival to the breeding ground.
