Species richness and pollen loads of hummingbirds using forest fragments in southern Costa Rica

In many areas of the humid tropics, relatively small patches of forest is t he habitat most commonly available for forest-dwelling organisms. To assess resident hummingbird use of forest fragments near the Las Cruces Biologica l Station in southwestern Costa Rica, we mist-netted birds in five fragment s (0.3-20 ha; ra 1300 m elev.) and the station's 226-ha forest preserve (Cd 900-1280 m elev.). From January 1994 through mid-March 1999, we recorded 1 069 captures of 21 hummingbird species during 49,900 net hours. Species ric hness, diversity indices, and capture rates increased asymptotically with p atch size, as expected. We captured 16 hummingbird species in both tile lar gest Fragment (20 ha) and in the nearby forest preserve. Non forest humming birds did not occur more frequently in the fragments than in the preserve, and all fragments supported a mixture of forest-interior and canopy-dwellin g hummingbird species, along with a diverse group of hummingbird-pollinated planes. Phaethornis guy was common at all sites and visited > 13 plans spe cies in the fragments during the 1998 dry season (based on analyses of poll en collected from the birds' heads). In contrast, Eutoxeres aquila was foun d at only the largest three sites (10, 20, and 22G ha) and carried pollen f rom only one plant species during the 1998 dry season. Lampornis castaneove ntris, a high-elevation hummingbird species, was far more common in the fra gments than in the preserve, while three species typically found at lower e levations were rare in the fragments and common in the preserve. These dist ribution patterns could be influenced by local climatic differences because the fragments are higher and receive more cloud mist and annual precipitat ion than the preserve. Our data show that pollen loads on hummingbird speci es vary, and this has implications for gene flow among hummingbird-pollinat ed plants. Although our results are consistent with previous reports that h ummingbird species may be less affected by deforestation than insectivorous avian species such as army ant followers, it is important to note that fro m the perspective of the generics and demographics of hummingbird-pollinate d plants, the important issue is whether appropriate pollinator species are able to move plant propagules among subpopulations of plants in fragmented landscapes. We conclude that the biodiversity of tropical forest fragments as small as 10 to 20 ha is high enough to warrant long-term preservation o f these areas, especially if they are located near larger tracts of forest.