A hierarchical analysis of nesting and foraging habitat for the conservation of the Hispaniolan White-winged crossbill ( Loxia leucoptera megaplaga)

Abstract

Little is known about habitat use by the endemic Hispaniolan White-winged crossbill ( Loxia leucoptera megaplaga), in part because of its small population size and wandering tendencies; before this study only a single nest had been described for the species. From 1996 to 1999 we studied crossbill abundance, and foraging and nesting habitat at three scales (individual tree, local patch, and landscape), in the Sierra de Bahoruco, Dominican Republic. Point-count estimates of the number of crossbills encountered in the 3 study sites varied significantly among years and sites (range=0.00–2.95 birds/ha), but we estimate that there may be as many as 3000 crossbills in the Sierra de Bahoruco and 3375 island-wide. Annual means of crossbill abundance were highly correlated with mean scores of pine cone abundance. Fifteen nests found in pine trees had a mean nest height of 14.2 m. Two nests were found at heights of 1.0 m and 1.5 m in understory shrubs of Lyonia sp. (Ericaceae). The mean age of 15 trees used for foraging or nesting by the crossbill was 96 years. The height of trees used for foraging was significantly greater, and bore significantly more cones, than randomly chosen cone-bearing trees from across the study sites. Results from our multivariate analyses of nesting and foraging habitat at the patch level suggest that crossbills favor sites that have taller, more densely spaced pine trees, and foraging sites contain more cones than are generally available. At the landscape level, both nesting and foraging results suggest that crossbills may respond negatively to fragmentation of the pine forest. Uncontrolled fires are the most important threat to pine forests and the persistence of the crossbill; our models suggest that at current burning regimes pine forest will be nearly eliminated within 100–150 years. Changes in the fire regime are probably human-caused and have altered the nature of fire in this system. Our study supports previous findings that expanses of mature pine are required by this species, but we also suggest protection of unfragmented areas with higher rates of canopy closure.