Demography of Hawai'i 'Elepaio: Variation with habitat disturbance and population density

From 1994 to 1997, 1 monitored 'Elepaio (Chasiempis sandwichensis), a forest bird endemic to Hawaii, in three sites that differed in either degree of habitat disturbance or population density. The goal was to determine whether areas with disturbed forest and reduced population density due to disease were lower-quality habitats that acted as population sinks. Sites where the forest had been disturbed by cattle grazing and timber harvesting contained larger 'Elepaio territories, supported less dense 'Elepaio populations, and had a higher proportion of subadult birds in the breeding population and, thus, can be considered lower-quality habitat for 'Elepaio. However, 'Elepaio populations in disturbed sites did not have lower survival, reproduction, or site fidelity than a population in denser forest, and they were self-sustaining. Disturbed sites were not population sinks maintained by immigration; they simply had a lower carrying capacity. Annual survival of territory-holders was high and was slightly higher in males (0.86 +/- 0.04 [mean +/- (SE)]) than in females (0.79 +/- 0.05). Fecundity was low, with pairs producing 0.56 +/- 0.06 fledglings per year, Site fidelity was high in males (0.98) and females (0.93), and most birds remained on the same territory for the duration of the study or until their presumed death. Population growth was stable at two sites ( lambda 0.96 +/- 0.03, 1.02 +/- 0.04) and increasing (1.12 +/- 0.04) at a site recovering from an epizootic of avian poxvirus. Young, subadult-plumaged males defended smaller territories and produced fewer fledglings than older males, but female age did not affect territory size or reproductive success. Recruitment age was younger where population density was lower.