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Diet selection is related to breeding status in two frugivorous hornbill species of Central Africa
- Aaron M. Lamperti, Aaron R. French, Ellen S. Dierenfeld, Mark K. Fogiel, Kenneth D. Whitney, Donald J. Stauffer, Kimberly M. Holbrook, Britta D. Hardesty, Connie J. Clark, John R. Poulsen, Benjamin C. Wang, Thomas B. Smith, V. Thomas Parker
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- Journal:
- Journal of Tropical Ecology / Volume 30 / Issue 4 / July 2014
- Published online by Cambridge University Press:
- 23 June 2014, pp. 273-290
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Avian diet selection is hypothesized to be sensitive to seasonal changes in breeding status, but few tests exist for frugivorous tropical birds. Frugivorous birds provide an interesting test case because fruits are relatively deficient in minerals critical for reproduction. Here, we quantify annual patterns of fruit availability and diet for two frugivorous hornbill (Bucerotidae) species over a 5.5-y period to test for patterns of diet selection. Data from the lowland tropical rain forest of the Dja Reserve, Cameroon, are used to generate two nutritional indices. One index estimates the nutrient concentration of the diet chosen by Ceratogymna atrata and Bycanistes albotibialis on a monthly basis using 3165 feeding observations combined with fruit pulp sample data. The second index is an estimate of nutrient concentration of a non-selective or neutral diet across the study area based on tree fruiting phenology, vegetation survey and fruit-pulp sample data. Fifty-nine fruit pulp samples representing 40 species were analysed for 16 nutrient categories to contribute to both indices. Pulp samples accounted for approximately 75% of the observed diets. The results support expected patterns of nutrient selection. The two hornbill species selected a diet rich in calcium during the early breeding season (significantly so for B. albotibialis in July and August). Through the brooding and fledging periods, they switched from a calcium-rich diet to one rich in iron and caloric content as well as supplemental protein in the form of invertebrates. Calcium, the calcium to phosphorus ratio and fat concentration were the strongest predictors of breeding success (significant for calcium and Ca:P for B. albotibialis in June). We conclude that hornbills actively select fruit based on nutritional concentration and mineral concentration and that the indices developed here are useful for assessing frugivore diet over time.
Seed dispersal by Ceratogymna hornbills in the Dja Reserve, Cameroon
- KENNETH D. WHITNEY, MARK K. FOGIEL, AARON M. LAMPERTI, KIMBERLY M. HOLBROOK, DONALD J. STAUFFER, BRITTA DENISE HARDESTY, V. THOMAS PARKER, THOMAS B. SMITH
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- Journal:
- Journal of Tropical Ecology / Volume 14 / Issue 3 / May 1998
- Published online by Cambridge University Press:
- 01 May 1998, pp. 351-371
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Seed dispersal is a process critical to the maintenance of tropical forests, yet little is known about the interactions of most dispersers with their communities. In the Dja Reserve, Cameroon, seed dispersal by the hornbills Certaogymna atrata, C. cylindricus and C. fistulator (Aves: Bucerotidae) was evaluated with respect to the taxonomic breadth of plants dispersed, location of seed deposition and effects on seed germination. Collectively, the three hornbill species consumed fruits from 59 tree and liana species, and likely provided dispersal for 56 of them. Hornbill-dispersed tree species composed 22% of the known tree flora of the site. Hornbill visit lengths, visit frequencies, and seed passage times indicated that few seeds were deposited beneath parent trees; in five hornbill/tree species pairings studied, 69–100% of the seeds ingested were deposited away from the parent trees. Germination trials showed that hornbill gut passage is gentle on seeds. Of 24 tree species tested, 23 germinated after passage by hornbills; of 17 planted with controls taken directly from trees, only four species showed evidence of inhibition of germination rate, while seven experienced unchanged germinated rates and six experienced enhanced germination rates. Results suggested that Certaogymna hornbill rank among the most important seed dispersers found in Afrotropical forests, and they deserve increased conservation attention. Ceratogymna hornbills are likely to become increasingly important in forest regeneration as populations of larger mammalian seed dispersers (such as forest elephants and primates) diminish.