© 1995 by The Society for Integrative and Comparative Biology
Effects of Aging and Mate Retention on Reproductive Success of Captive Female Peregrine Falcons1
The Peregrine Fund, Inc. 5666 W. Flying Hawk Lane, Boise, Idaho 83709
SYNOPSIS. Separating ecological (extrinsic) factors affecting reproduction from physiological and experiential (intrinsic) factors can be problematic in free-ranging animals. This study examined age-related changes in six measures of reproductive success (clutch size, fertility, hatchability, brood size at hatching, survivorship of nestlings, and brood size at fledging) for captive female peregrine falcons (Falco peregrinus) where ecological factors (i.e., access to mates, nesting sites, and food) were not limiting and were similar across years and between individuals. Mean nestling survivorship increased throughout the lifespan of the female while all other measures of reproduction peaked at about seven years of age and decreased thereafter. Birds with prior breeding experience had higher productivity than inexperienced birds of the same age. Productivity increased with increasing experience of the pair. Productivity dropped by an average of 53% when females experienced a change of mate, and then subsequently increased over a period of several years. Productivity was not affected when birds were moved to different breeding sites. There was no evidence that early improvements in reproduction were related to chronological aging in the absence of experiential differences. Birds that began breeding earlier produced more fledglings during their lifetimes as a result of higher annual productivity. Lifetime reproduction was not correlated with longevity because birds with higher maximal egg production had shorter breeding lifespans. Birds retaining mates produced more fledglings during their lifetime than birds that changed mates, but birds that changed mates more than once did not have lower lifetime reproduction than birds that had only one mate change. These results suggest that 1) age-related changes in reproduction are not necessarily resource-mediated, 2) in the absence of resource limitation, experience of the pair is a primary factor determining annual reproductive success, 3) benefits of increasing experience may be offset by the onset of senescence, 4) the cost of present egg production on future reproductive potential supports a "pleiotropic" theory of aging, and 5) costs associated with mate changes may encourage selection for low "divorce" rates (i.e., lifetime monogamy) in this species.