Habitat selection and population trends in terrestrial bird species of Robinson Crusoe Island: habitat generalists versus forest specialists

Abstract

Habitat loss and degradation on oceanic islands are key processes leading to population decline of endemic birds and facilitating the establishment of invasive bird species. In this study, carried out in the Robinson Crusoe Island, we assessed density and habitat selection of terrestrial bird species, including juan fernandez firecrown and juan fernandez tit-tyrant, two endemics, as well as green-backed firecrown and austral thrush, which apparently originate from the mainland. Results show that perturbed habitats contained a low density of the endemic species whereas the mainland species were significantly more abundant in perturbed scrub habitats. Bird species show different habitat selection patterns, with endemics selecting for native forest and mainland species selecting for perturbed habitats, or using them at random. Bird species experienced temporal trends in their overall population sizes, with the endemic tit-tyrant suffering a significant decline in its population size of about 63% between 1994 and 2009. Only mainland species exhibited temporal changes in habitat use, significantly reducing their densities in the preferred scrub habitats, possibly as a response to decreased habitat quality. Thrushes apparently were able to compensate the population decrease in one non native habitat type by using native forests, a habitat giving them the opportunity of preying on nests of endemic species. We conclude that endemic bird species behave as specialists whereas the mainland species must be treated as invasive generalists on Robinson Crusoe Island.

Resource use in two contrasting habitat types raises different challenges for the conservation of the dryad butterfly Minois dryas

“…Bell et al 2001;Bonte et al 2002;Mildenstein et al 2005;Skórka et al 2006;Hahn et al 2011). These habitat types are sometimes so distinctive in terms of their resources, vegetation and structure that the behavior and biology of a species may differ substantially depending upon the type (Boudjemadi et al 1999;Potts et al 2001;Allen and Thompson 2010).…”

First description of the micro-habitat selection pattern of the island endemic Juan Fernandez Tit-tyrant

“…Because their populations have natural small sizes and have been exposed to a long-term historical isolation, bird species endemic to oceanic islands tend to have higher extinction rates than their mainland relatives (Loehle and Eschenbach 2012). In addition, the level of specialization of endemic island birds to native habitats which are being lost and disturbed by humans could contribute importantly to increase their extinction risk (Hahn et al 2011a, Cofré 1999.…”

“…Previous studies suggest that this tit-tyrant species prefers to use native forests instead of human-associated habitats with their nests being located in the native canopy (Hahn et al 2005(Hahn et al , 2011a(Hahn et al , 2011b. The loss and degradation of native forest by human activities and introduced herbivores currently represents the major conservation problem for species endemic to Robinson Crusoe like tit-tyrants (Cuevas and van Leersum 2001;Ricci 2006).…”

“…The loss and degradation of native forest by human activities and introduced herbivores currently represents the major conservation problem for species endemic to Robinson Crusoe like tit-tyrants (Cuevas and van Leersum 2001;Ricci 2006). This habitat loss has contributed to the reduction of the population size of the tit-tyrant, which has experienced a signifi cant decline of about 63 percent during the last 15 years (Hahn et al 2011a). …”

Do beavers improve the habitat quality for Magellanic Woodpeckers?

“…Humans can indirectly contribute to the degradation of bird habitats by introducing mammal species that feed on trees and alter forest ecosystems, including feral goats, rabbits, feral cattle, hogs, and beavers (Hahn et al 2011).…”