BODY SIZE AND THE OCCURRENCE OF AVIAN SPECIES ON LAND-BRIDGE ISLANDS

The author tested for biogeographic patterns of size-related avian occurrence on 7 Neotropical land-bridge islands (Trinidad, Tobago, Margarita, Aruba, San Jose, Rey and Coiba). Both within and between avian families, there was a slight excess of large-bodied species on islands, compared to mainland source pools, ie no evidence that large-bodied species are extinction-prone and no evidence of size-related, ecological truncation at the family level. Neotropical land-bridge islands are separated from the mainland by relatively narrow water gaps, and there have probably been numerous opportunities for recolonization during the past 10 000 yr of "isolation'. Fifteen mainland species occurred on mesic land-bridge islands (Trinidad, Tobago, San Jose, Rey and Coiba) whenever appropriate habitat was present. These persistent species were usually associated with second-growth, clearings, and residential areas. Thirty-two mainland species were never found on land-bridge islands despite the presence of appropriate habitat. These missing species were mostly associated with primary and second-growth forest. At least some of the species that never occur on land-bridge islands thus may be extinction-prone. This list includes representatives from 17 avian families and several diverse foraging guilds. The range of body masses spans almost 3 orders of magnitude (6-650 g). With respect to body size, there are no simplified "rules' for predicting the occurrence of most Neotropical bird species in insular communities, but species that are often missing from land-bridge islands are primarily associated with primary or second-growth forest. -from Authors