Ramphastos Sulfuratus Research Articles

Removal of Wild Nutmeg (Virola Surinamensis) Crops by Birds

We observed birds and mammals visiting individual plants in a Panamanian population of the rainforest tree Virola surinamensis (Wild Nutmeg) to determine (1) relative importance of different dispersal agents, and (2) the relationships between crop size, crop quality, and seed removal. Arils of this tree are exceptionally nutritious (63% fat, 9% nonstructural carbohydrate, 3% protein), but draw remarkably few species of fruit—eating animals. Six birds take 77% of the seeds handled by animals. One toucan (Ramphastos°swainsonii) accounts for 35% of the seeds handled; other birds (Penelope purpurascens, Trogon massena, Baryphthengus martii, Pteroglossus torquatus, Ramphastos sulfuratus) play lesser roles. The smallest visitor, a cotinga (Tityra semifasciata) eats arils but does not disperse seeds. One monkey (Ateles geoffroyi) removes 3% of the seeds handled by frugivores, but smells and rejects or otherwise wastes 9%. Such a small assemblage is anomalous in a forest with at least 78 species of fruit—eating animals; other trees with arillate seeds of similar size draw as many as 23 frugivores. We hypothesize that the size of the assemblage is limited by seed size, small crop size, and perhaps by defensive compounds in the arils. Despite the small assemblage, an average of 62% (range: 13—91%) of the fruits available to animals are taken. Fruits are so nutritious that trees with both small and large crops are depleted; no variance in the percentage of seeds removed can be attributed to crop size. Fruits of different individual trees do vary in size; 59% of the variation in the percentage of seeds taken can be attributed to mean seed size. Fruit—eating animals preferentially deplete trees with small seeds, and coincidentally favor trees with high aril—to—seed ratios. No significant portion of the variance in dispersal success can be explained by aril mass alone. We hypothesize that consistent differences in seed size could result in dramatic differences in dispersal, and hence reproduction, over the lifetime of individual trees. On the other hand, selection may alternatively favor small seed size and high dispersability in years when frugivores are abundant, and large seed size and enhanced seedling vigor in the parental stand when fruit—eating birds are scarce. Small—seeded plants are likely to colonize new sites; large—seeded individuals are likely to produce offspring that fare well in competition with other seedlings near parent trees.

Bird Activity and Seed Dispersal of a Tropical Wet Forest Tree

Feeding assemblages of birds were observed throughout a fruiting season at a Costa Rican population of the rain forest tree Casearia corymbosa in order to distinguish effective dispersal agents from visitors which used arils for food without dispersing seeds. This system is of special interest because the tree fruits during an annual period of fruit scarcity in a forest characterized by high proportions of animal—dispersed plants and obligate frugivores. Results show that the Masked Tityra (Tityra semifasciata) is an effective dispersal agent of seeds of this tree because it: (1) regurgitates viable seeds, (2) is a common and regular visitor throughout the season, (3) has high feeding rates, (4) removes seeds from the vicinity of the parent tree before processing them, and (5) depends on this rather than other plants fruiting at the same time. Twenty—one other visitors were deficient dispersers, although some depended heavily on fruit of this tree for food. Two parrots (Amazona autumnalis and Amazona farinosa) preclude dispersal by stripping arils with their bills and dropping all seeds in situ. Fourteen species are occasional visitors. Five visitors (Ramphastos sulfuratus, Ramphastos swainsonii, Pteroglossus torquatus, Myiozetetes similis, and Myiozetetes grandensis) process seeds undamaged and sometimes numerically abundant, but are absent part of the season and tend to regurgitate seeds in situ. Because fruiting activity of this tree occurs during annual scarcity, it represents a pivotal species in the community. Three obligate frugivores, including one effective disperser and two fruit thieves, depend almost entirely on it for food periods of 2—6 wk. I hypothesize that extinction of this plant at this site would lead to disappearance of these birds, and would almost certainly depress recruitment of other species of trees for which they serve as dispersal agents at other times of the year.

Differential Seed Dispersal by Birds of the Tree Casearia nitida (Flacourtiaceae)

Data are presented which demonstrate (1) flight patterns of frugivorous birds are responsible for directional patterns of seed dispersal, (2) these patterns influence seed mortality, and (3) dispersal of seeds away from the parent tree is more likely to result from behaviors characteristic of obligate frugivores (Ramphastos sulfuratus and R. swainsonii) than frugivore/insectivores (Myiozetetes similts and M. granadensis). Investment by the parent tree in a seed carried by a frugivore is less likely to be wasted than investment in a seed carried by an frugivore because specialists are more likely to carry seeds away from areas of high seed mortality than opportunists. PLANTS HAVE A VARIETY OF CHARACTERISTICS which result in dispersal of their seeds by fruiteating animals. These involve the structure of the fruit (van der Pijl 1969) or other aspects of plant reproductive biology (Snow 1965; Smythe 1970; Snow 1971). Previous studies consider the effects of treatment by the digestive tract on the germination of seeds (Darwin 1859; Kerner 1897; Rick and Bowman 1961), the effects of long-distance dispersal on the biogeography of plants (Cruden 1966; Carlquist 1974), effects of dispersal on the survivorship of seeds which suffer high levels of animal predation (janzen 1971), and the expected influence of such predation on the local dispersion of plants (Janzen 1970). The variety and abundance of fruits in the tropics is correlated with a diverse bird fauna showing varying degrees of specialization for frugivory and seed dispersal (Wetmore 1914; Keast 1958; Orians 1969; Karr 1971; Morton 1973). Absent frcm previous studies are quantitative data showing the patterns of seed distribution produced by movements of different kinds of dispersers and the effects of this dispersal on the survivorship of seeds. Such information is particularly desirable in view of McKey's (1975) argument that the dispersal of seeds by specialized birds which are obligate frugivores should be qualitatively different from dispersal by opportunistic birds which facultatively feed on fruit or insects. If this point of view accurately reflects close coevolutionary relationships between obligate frugivores and the plants upon which they feed, we predict that specialists should also produce patterns of seed distribution and resulting seed mortality more beneficial to the plant than those produced by birds with less dependence on fruit. This paper offers a partial test of this prediction and suggests further research which will elucidate relationships between plants and their dispersal

Life History of the Keel-Billed Toucan

TOUCANS are among the most characteristic birds of tropical America, and for well over a century they have probably been depicted, in drawings and words, more frequently than any other neotropical family except hummingbirds. Yet even today there is a dearth of information about their habits, especially their nesting. Beebe (Beebe et al., 1917) described the nests, eggs, or nestlings of several toucans of British Guiana. Van Tyne (1929) made a careful study of the breeding habits of the Keel-billed Toucan (Ramphastos suiphuratus) in Panama, but his observations were cut short by the destruction of the nestlings. Wagner (1944) published notes on the breeding of the Emerald Toucanet (Aulacorhynchus prasinus) in southern Mexico. Apparently the earliest account of all stages in the nesting of a toucan, from laying to the departure of the nestlings, was my life history of the Blue-throated Toucanet (A. caeruleogularis) (Skutch, 1944). Important details of the nesting of this small highland toucan were added in a later account (Skutch, 1967). Observations on the breeding and general behavior of two species of middle-sized ara~ari toucans were recorded in another paper (Skutch, 1958). The present contribution to the natural history of toucans is based largely upon studies made at Finca La Selva in 1967 and 1968. This property, largely covered by primeval rain forest but with extensive riverside plantations of cacao, lies along the left bank of the Rio Puerto Viejo just above its confluence with the Rio Sarapiqui, a tributary of the Rio San Juan in the Caribbean lowlands of northern Costa Rica. Slud (1960) has well described the lofty, epiphyte-burdened forest with an undergrowth consisting largely of small palms, and given an account of its avifauna remarkably rich in species. Including their enormous bills, adult Keel-billed Toucans (which in other writings I have called Rainbow-billed Toucans) range from about 17 to 22 inches in length. Even without the many-hued bill, this toucan with contrasting areas of white, yellow, red, and black would be a spectacular bird; attached to a boldly patterned body, the delicately tinted bill makes it one of the most colorful inhabitants of the Central American forests. In the southern race (R. s. brevicarinatus), the greater part of the swollen upper mandible is yellowish green; there is an elongated patch of bright orange along the basal half of its cutting edge; and the terminal fifth (approximately) is dull red. The lower mandible is green at the base, then light blue, then dull red on approximately the terminal eighth. Both man-