RARITY AND VULNERABILITY - THE BIRDS OF THE CORDILLERA CENTRAL OF COLOMBIA

The rarity of an organism is widely accepted as a good predictor of vulnerability, but rarity has been interpreted in a variety of ways. Rabinowitz et al. (1986) defined three dimensions of rarity for an analysis of the flora of the British Isles: geographic distribution, habitat specificity, and local population size. They found the three factors to be independent, that is, each factor provides information not provided by the other two. In this paper, the method of Rabinowitz et al. is used to analyze the vulnerability of the loud forest avifauna of the Cordillera Central of Colombia. The method is extended by assigning a vulnerability index to each form of rarity and analyzing its taxonomic and ecological correlates. I found that the three factors are not independent. Species with wide geographic distribution tend to have broad habitat specificity and high population densities. One-third of the species have low population density, and most of these have restricted habitat specificity and narrow geographic ranges. Forty-five percent of the birds in this sample are highly vulnerable because they have narrow distributions and require forest habitats. The taxonomic and ecological analyses reveal that some groups of species are particularly vulnerable. Among insectivorous birds, woodcreepers, spinetails, and antbirds seem to be very vulnerable because they depend on forest habitats. Raptors show no clear pattern, but for frugivores a clear pattern emerges. Some families (e.g., parrots, cotingas), seem to be consistently vulnerable, independent of body size. Tanagers show a significant correlation between body size and vulnerability. An analysis of local vulnerability (determined by habitat specificity and population size, regardless of distribution) reveals that frugivorous birds of restricted habitat specificity are significantly larger. Similar findings have been reported by other studies. The three-dimensional classification of rarity used in this study provides a rapid, albeit preliminary, approach to identifying vulnerable species. To develop management practices adapted to each particular case, careful analysis of life history traits and detailed population and community studies are required.