Ecological and behavioral correlates of mating behavior and breeding success in western bluebirds, Sialia mexicana

Reproductive success can be affected by ecological variables, as well as characteristics of individuals. Examination of the correlates of reproductive success requires a thorough understanding of the natural history of a species. In this study we (1) present a comprehensive literature review of the natural history of western bluebirds, Sialia mexicana; (2) examine the relationship between breeding synchrony and nesting density on mate-guarding and nest-guarding; and, (3) examine the correlation of breeding synchrony, density, insect availability, and parental age, foraging skill, and care with measures of reproductive output.;Western bluebird males behave in ways consistent with guarding their paternity by remaining closer to females and following them more often when they are fertile than when they are incubating. Mate-guarding was not correlated with breeding density, but pairs maintained a greater distance apart and were within 20 m of each other less often as synchrony increased. Female distance from the nest did not vary between egg-laying and incubation, but females remained closer to their nests as density increased, and this was especially significant at synchronous nests.;Breeding density was negatively correlated with clutch size and positively correlated with age at fledging. Synchrony was positively correlated with clutch size and brood size. Predation was negatively correlated with breeding synchrony, but few nests were lost to predation. Insect availability was positively correlated with nestling condition. Females, but not males, adjusted their feeding rate to brood size. Successful female foragers initiated first clutches sooner than less successful foragers. The provisioning rate of females, and to a lesser extent, males, increased with increased insect availability, but nestling condition was not correlated with measures of parental care. Second-year females had higher hatching success than older females. Male age was unrelated to any measure of reproductive success of females.