Meeting Abstract
To avoid harsh conditions at their breeding grounds, many birds migrate south during the winter. Individuals migrating to a more southern location may experience more favorable conditions but at the cost of a long, energetically-demanding migration that may delay their spring reproductive development. The relationship between migration distance and reproduction has primarily been investigated in monogamous species with a focus on early season testosterone production in both males and females. Our study presents a new perspective by assessing the importance of migration distance in a polygynous species with increased pressure for both males and females to arrive and breed early. Males that arrive early are able to compete for high-quality territories while the nests of females that lay earlier receive increased paternal care. We collected blood and claw samples from male and female red-winged blackbirds (Agelaius phoeniceus) before breeding began in the Alice Waterfowl Production Area in North Dakota. We measured baseline levels of estradiol and testosterone in females and baseline and GnRH-induced testosterone levels in males. We estimated the migration distance of an individual using stable isotopes of hydrogen from a claw sample. We predict that males with shorter migration distances will have higher baseline and post-GnRH testosterone levels, larger harems, and more offspring. Similarly, we predict that females with shorter migration distances will have elevated baseline estradiol and testosterone levels, earlier lay dates, and more offspring.
