Article
Plasma Luteinizing Hormone, Steroid Hormones, Behavioral Role, and Nest Stage in Cooperatively Breeding Harris' Hawks (Parabuteo unicinctus)
The Auk
(1991)
Abstract
We measured plasma levels of testosterone (T), estradiol17{3 (E), corticosterone,
and luteinizing hormone (LH) in adult breeders, adult-plumaged helpers, and juvenal-plumaged
helpers of the cooperatively breeding Harris' Hawk (Parabuteo unicinctus) in southeastern
Arizona. In the males, both adult breeders and most adult-plumaged helpers had elevated T
and LH during February and March, when nest building occurs, whereas most juvenalplumaged
helpers showed no change in LH, T, or E throughout the year. Thus adult-plumaged
helpers, usually not related to the breeders, are hormonally ready to breed in the spring. We
suggest that these helpers attain breeding readiness because potential benefits they can derive
from either occasional successful copulations or possible attainment of the breeding position
make reproductive readiness advantageous. In contrast, most juvenal-plumaged helpers are
aiding their own parents on their natal territory and are not hormonally ready to breed, and
thus they physiologically avoid the potential for inbreeding. An exception to this was a
juvenal-plumaged male helper with elevated testosterone levels who was not helping his
parents. The female breeders we examined had elevated T, LH, and E during the nest-building
period, whereas the helpers (both adult- and juvenal-plumaged) did not show elevations at
any time of the year. During the early part of the nesting cycle, the adult-plumaged female
helpers weighed significantly less (ca. 10%) than the breeders. It is possible that poor body
condition, subordinate status to the breeding females, or both were related to their lack of
breeding readiness. In all birds, corticosterone levels increased with handling time, and were
higher during the nesting periods than during non-nesting periods, but showed no consistent
relation with helper or breeder status. As in other species that are relatively social, maintain
long-term pair bonds, or are tropical in distribution, plasma concentrations of LH and sex
steroids in Harris' Hawks, even when elevated, were relatively low.
Disciplines
Publication Date
July, 1991
DOI
10.2307/4088103
Publisher Statement
The Auk © 1991 American Ornithologists' Union
Citation Information
Nora A. Mays, Carol M. Vleck and James Dawson. "Plasma Luteinizing Hormone, Steroid Hormones, Behavioral Role, and Nest Stage in Cooperatively Breeding Harris' Hawks (Parabuteo unicinctus)" The Auk Vol. 108 Iss. 3 (1991) p. 619 - 637 Available at: http://works.bepress.com/carol-vleck/15/