David F. Whitacre

A Comparison of the Phyllostomid Bat Assemblages in Undisturbed Neotropical Forest and in Forest Fragments of a Slash-and-Burn Farming Mosaic in Petén, Guatemala1

Using mist nets, we compared phyllostomid bat ensembles of continuous mature forest in Tikal National Park, Guatemala, and of forest fragments in the nearby farming landscape. Of 20 species captured, 13 were shared between treatments, 4 were unique to continuous forest, and 3 were unique to forest fragments. Dominance-diversity curves were similar for the two treatments except that Sturnira lilium comprised 43 percent of captures in the forest fragments, resulting in greater dominance there. Capture rates (and presumably relative abundance) differed significantly between continuous forest and forest fragments, both in terms of species and feeding guilds. Sturnia lilium and Dermanura sp. were captured significantly more often in forest fragments than in continuous forest, whereas Artibeus jamaicensis, A. Izturatus, and Centurio senex were taken significantly more often in continuous forest. Large frugivores accounted for a higher proportion of total captures in conrinuous forest than in forest fragments, whereas small frugivores showed the opposite pattern. By their abundances, Carollia perspicilkzta and S. lilium are indicators of forest disturbance. The relative abundances of large frugivores, which feed on large fruits of mature forest trees, and small frugivores, which fced on small-fruited plants occurring in early succession, are an indicator of forest disturbance. Other groups, such as large insectand vertebrate-eating bats, because of their low capture rates, are impractical as indicators for rapid assessment of forest disturbance based on mist netting, but may prove especially vulnerable to forest fragmentation.

The Orange-breasted Falcon Falco deiroleucus in Mesoamerica: a vulnerable, disjunct population?

The Orange-breasted Falcon Falco deiroleucus , among the worlds most poorly known falcons, is sparsely distributed in Neotropical forests from south-east Mexico or Guatemala to Paraguay and northern Argentina. Details of distribution and population size are poorly known throughout the speciess range. From 1992 to 1997 we studied this species at 19 nest sites in Guatemala and Belize. Occupancy and productivity rates remained stable for this northernmost population over this six-year period. Sparse data on historical distribution preclude a full assessment of possible changes in population status in the Mesoamerican portion of the speciess range. Today the species appears restricted to forested areas in conjunction with large nesting cliffs. No breeding record is known for any Mesoamerican nation except Belize and Guatemala. Mean number of fledglings per successful nesting was significantly higher in areas of predominantly forested mosaic habitat (2.11, n = 18) than at sites with uninterrupted mature forest (1.36, n = 11); proportion of sites occupied and of pairs fledging young did not differ between these two habitats. Based on historical and current distribution records and distribution of potential nesting habitat, we conclude that the Guatemala/Belize opulation of Orange-breasted Falcons is disjunct from the speciess main range in South America, is perhaps the only local population (at best one of a small number) in Mesoamerica, and is tightly linked to the existence of suitable nesting cliffs combined with large forested areas.

BEHAVIOR, DIET, AND BREEDING BIOLOGY OF DOUBLE-TOOTHED KITES AT A GUATEMALAN LOWLAND SITE

Abstract We studied Double-toothed Kites (Harpagus bidentatus) in tropical lowland forest at Tikal National Park, Petén, Guatemala, documenting behavior and diet during the incubation and nestling periods. These 200-g kites are Accipiter-like in form and strikingly size-dimorphic for a kite. Modal clutch size was two, producing 0.63 fledglings per nesting attempt and 1.25 per successful nest. Nesting was largely synchronous among pairs, with hatching during the first month of the rainy season and fledging one month later. Incubation lasted 42–45 days and nestlings fledged at 29.5 days on average. A radio-tagged fledgling was fed near the nest for 35 days; 6–8 weeks after fledging it dispersed at least 10 km, presumably reaching independence. Males did not incubate or brood, and rarely fed nestlings directly. Males typically provided most but not all prey (mainly lizards) during incubation and early nestling periods. Insects in the nestling diet increased through the nestling period as females increasingly hunted, often bringing in insects. These kites hunted from perches, below and within the closed canopy of tall, mature forest, taking 60.5% insects, 38.1% lizards, and 1.4% other vertebrates; vertebrates comprised at least 75% of prey biomass. Most prey were taken from vegetation, but prey in flight also were captured. Active, adjacent nests averaged 1.35 km apart, for a maximum density estimate of 0.60 pairs km−2 and a more likely estimate of 0.33–0.50 pairs km−2 in homogeneous, favorable habitat and 0.29–0.44 pairs km−2 for Tikal National Park as a whole.

Roadside hawk breeding ecology in forest and farming landscapes

Abstract We compared breeding ecology, density, and reproductive success of Roadside Hawks (Buteo magnirostris) in two Guatemalan study areas during 1993 and 1994. Primary forest supported 1.15 territorial pairs/km2 whereas a slash-and-burn farming landscape supported 1.41 territorial pairs/km2. All nests (n = 32) were in emergent trees. Hawks nested selectively in low canopy, seasonally inundated primary forest, and spacing of nests was related to the distribution of this forest type. Pairs did not nest selectively in a particular habitat in the farming landscape, but nested in isolated, emergent trees. Nest success (proportion of attempts that produced ≥1 fledgling) was 0.17 in the forested area and 0.30 in the farming landscape. Productivity (fledglings per territorial pair) was 0.08 in the forest and 0.32 in the farming landscape. Incidence of non-nesting by territorial pairs was greater in the forest (50%) than in the farming area (20%). The overall rate of nesting by territorial pairs was 65%. The most frequently identified cause of nest failure in the farming landscape was human persecution, while in the forest it was predation. Prey delivery rates did not differ significantly between habitats.