Habitat use and resource tracking by African Ceratogymna hornbills: implications for seed dispersal and forest conservation

Abstract

Conservation of tropical forests requires an understanding of the seasonal patterns of abundance and distribution of important seed dispersers. In the forests of Central Africa, three species of hornbills in the genus Ceratogymna (Aves: Bucerotidae) provide dispersal for over 50 species of trees and lianas, yet their ecology is poorly known. We present the first empirical evidence for resource tracking and large-scale movements by two of these species, which were previously considered resident. Hornbill numbers and fruit production were estimated over a one-year period in the Dja Reserve, Cameroon. Monthly abundances of C. atrata and C. cylindricus varied four-and 12-fold, respectively, and were predicted by community fruit availability as measured by fruitfall on a 4·3 km trail. In contrast, C. fistulator abundances varied little and were not related to fruit availability. Synchronous population fluctuations in sites 22 km distant were observed for atrata and cylindricus, but not for fistulator. Together, these results indicate that atrata and cylindricus populations track fruit resources via seasonal emigrations, while the fistulator population appears to be relatively sedentary. Comparisons of hornbill densities in primary and secondary forests suggest that they are important dispersers in both habitats, and will likely play larger roles in central African forest regeneration as more vulnerable seed dispersers are removed by hunting. If large seasonal movements of hornbills turn out to be a general phenomenon, effective management of central African forest reserves will require greater emphasis on reserve connectivity and on seasonal and spatial patterns of fruit production.1 All correspondence to: Kenneth D. Whitney Present address: Center for Population Biology, University of California, Davis, California 95616-8755, USA.evaluating the effects of disturbance on particular dispersers.Disperser populations in tropical forests are also highly affected by the availability of fruit. Fruit exhibits a high degree of spatial and temporal patchiness in most tropical forests (Fleming, Breitwisch & Whitesides, 1987;Fleming, 1992;Jordano, 1992;van Schaik, Terborgh & Wright, 1993). Periods of fruit scarcity and abundance have been related to seasonal cycles of rainfall (Foster, 1982;Fleming et al., 1987), temperature (Tutin & Fernandez, 1993), and insolation (White, 1994a), and are likely controlled by the interaction of these and a variety of other factors (van Schaik et al., 1993). Spatially, large differences in fruit availability have been recorded over distances as small as 2 km (van Schaik, 1986). Frugivores can respond to this spatiotemporal patchiness through resource tracking, with consequences for their demography, physiology, foraging movements, social organization, and mating systems (Fleming, 1992). Resource tracking via daily and/or seasonal foraging movements has been demonstrated for many frugivore taxa; recent discussions include Fleming (1992), Jordano (1992), and van Schaik et al. (1993). Flem...

Seasonal variation in the feeding ecology of the grey‐cheeked mangabey (Lophocebus albigena) in Cameroon

“…The vegetation is semideciduous tropical rain forest [Letouzey, 1968], and has never been logged. Small-scale agriculture took place at one corner of the study site more than 90 years ago [Whitney & Smith, 1998], but the only evidence of farming is a small patch (<25 m 2 ) of thick Marantaceae shrubs devoid of large trees. The main study area contains primary forest, Uapaca swamp, Raphia swamp, and inselberg (rock outcroppings frequently covered by shallow soils and grasses) habitat.…”

Seed dispersal of woody plants in tropical forests: concepts, examples and future directions

“…In general, dietary requirements and fruit availability shift seasonally and regionally, with many species of large frugivorous animals tracking different fruit resources as they become available throughout the year (Blake & Loiselle 1991;Whitney & Smith 1998). The disperser assemblage of a given tree species can vary with habitat, as Howe and Vande Kerckhove (1979) found for Casearia carymbosa at wet-and dry-forest sites in Panama.…”

The spatial scale of plant–animal interactions: effects of resource availability and habitat structure

“…In all studied ecosystems, and independently of the effect of habitat structure, large-scale bird clumps occurred in fruit-rich patches, suggesting a pervasive and generalized process of fruit resource tracking across the whole landscape. Large-scale fruit tracking by birds has been evidenced for other temperate and non-temperate ecosystems (e.g., Whitney and Smith 1998, Tellerı´a and Pe´rez-Tris 2003, Guitia´n and Munilla 2008, Wehnke et al 2009). Strong vagility, flocking behavior, and an almost exclusively fruit-based diet of temperate migrant passerines during autumn and winter (e.g., Turdus spp.…”