Species diversity, winter-site fidelity, & ecology of winter resident ‘landbirds’ in Costa Rican mangroves

Abstract

Data from the North American Breeding Bird Survey indicate that populations of many species of neo-tropical migrant birds have declined over the past three decades. Processes operating during the non-breeding season may be particularly important in driving declines, yet data linking wintering and breeding populations are currently few. The scarcity of data on the winter ecology of neo-tropical migrants is especially alarming because most natural habitats in Central America (where most of these species over-winter) are currently considered “vulnerable, threatened, or endangered” due to direct human impacts. Wetland habitats, such as mangrove and riparian forests along the Pacific Flyway are particularly important for over-wintering bird species that breed in North America. Development and ranching is severely impacting these habitats; thus, information that leads to the conservation of important areas for birds and other wildlife is critically needed. Here we report on the results and observations of four winters banding in Costa Rican mangroves. Populations of landbirds were sampled at 4 sites in Guanacaste, Costa Rica using constant-effort mist-netting and banding (Baillie et al 1986), mid-November through mid-March 2003/2007. The total effort was 20,269 mist-net hours. We participated in and followed the protocol of the MoSI (Monitoreo de Sobrevivencia Invernal) program (DeSante et al 2004). Three of the study sites were located in areas of mangrove swamps dominated by Black Mangroves Avicennia germinans in the Southern Dry Pacific Coast Mangroves ecoregion; a fourth site was sampled in the Central American Dry Forest ecoregion. A total of 3,980 individual birds were captured, 3,015 of these birds were banded with numbered US F&W bands, and 965 resident ‘tropical’ birds were captured but released unbanded; selected species were however marked with unique combinations of color bands. Approximately 84% (2,502) of all the birds captured were neo-tropical migrants, 50% of these were migratory warblers (9 species) and 20% of all the birds captured were Prothonotary Warblers (Protonotaria citrea). There were 1,744 recapture events involving 1,199 individual birds. Among-year site fidelity was documented for 441 birds of 34 species. Within year site fidelity was documented for 758 birds of 29 species. Warblers accounted for over 80% of all recaptures, 31% were Prothonotary Warblers and 23% were Northern Waterthrush (Seiurus noveboracensis). Sixty-three birds of 7 species were recaptured after moving between mangrove and dry forest habitats about a kilometer apart: Brown-crested Flycatcher, Great Kiskadee, Northern Waterthrush, Prothonotary Warbler, Tennessee Warbler, and Yellow Warbler. A foreign recovery was made of a Tennessee Warbler banded at Delta Marsh Bird Observatory, Manitoba, Canada. Banding results show that mangrove swamps in Costa Rica provide important wintering habitat for migratory Passerines from North America and that individual birds show strong site fidelity. Results also show that some Passerines use the mangrove swamps mostly for roosting at night and leave the swamps in early morning to spend much of the day foraging in adjacent ‘Central American Dry Forest’.