Exploitation of a Seasonal Resource by Nonbreeding Plain and White-crowned Pigeons: Implications for Conservation of Tropical Dry Forests

—Columbids often exhibit irregular movement patterns in response to fruit abundance. We tested whether the abundance of nonbreeding Plain (Columba inornata) and White-crowned (C. leucocephala) pigeons was correlated with Thrinax parviflora fruit production in a dry forest in southeastern Jamaica. Monthly, from November to March, we counted the number of pigeons leaving the forest to roost in an adjacent mangrove swamp. Within two days of each roost count, we also counted all fruits on ten T. parviflora trees in the forest. Columbid and fruit counts showed similar patterns of temporal abundance, with increases from November to January and decreases from January to March. Peak (January) counts of White-crowned Pigeon, Plain Pigeon, and unidentified columbids were 129, 77, and 151, respectively. The peak Plain Pigeon count was approximately three times greater than the highest counts previously recorded for Jamaica. These data indicate that the Portland Ridge dry forest may provide a critical resource for the Plain Pigeon, perhaps at a time when fruit abundance is low on other parts of the island. Given the globally significant number of Plain Pigeons that use this site, protection from further development should be a priority. Received 8 June 2000, accepted 24 January 2001. The irregular temporal and spatial pattern of fruit abundance has been well documented and is thought to be a result of variation in climatic conditions such as temperature and rainfall, as well as interspecific variation in fruiting phenologies (Janzen 1967, Smythe 1970, Frankie et al. 1974, Crome 1975, Foster 1982). This variation in resource abundance is likely the ecological basis behind the irregular to nomadic distribution patterns of many frugivores (Wheelwright 1983, Levey 1988, Blake and Loiselle 1991, Loiselle and Blake 1991). Indeed, frugivory may be a precursor to migratory behavior (Levey and Stiles 1992). Many columbiforms are frugivorous and exhibit movement patterns that range from nomadic to migratory, presumably in response to the temporal and spatial distribution of fruit availability (Crome 1975, Frith et al. 1976, Wiley 1979, Innis 1989, Lambert 1989, Milan-Rivera 1992). In the Caribbean, the genus Columba is represented by four native species, three of which occur regularly on Jamaica. 1 Dept. of Ecology and Evolutionary Biology, Tulane Univ., 310 Dinwiddie Hall, New Orleans, LA 70118. 2 Present address: Univ. of Vermont, School of Natural Resources, Aiken Center, Burlington, VT 05405. 3 Present address: Dept. of Wildlife, Humboldt State Univ., Arcata, CA 95521. 4 Corresponding author; E-mail: astrong@nature. snr.uvm.edu These three species feed nearly exclusively on fruits, and are probably important seed dispersers (Bancroft and Bowman 1994, Strong and Bancroft 1994, Baptista et al. 1997). The Ring-tailed Pigeon (C. caribaea) is found at relatively high elevations whereas the Plain Pigeon (C. inornata) and the White-crowned Pigeon (C. leucocephala) generally prefer lower elevations (Downer and Sutton 1990). Of these two lower elevation species, the White-crowned Pigeon is relatively common on Jamaica, but little is known about the distribution and abundance of the Plain Pigeon, which was recently reported as possibly extirpated from Jamaica (Miyamoto et al. 1994). In January 1996, we observed 16 Plain Pigeons flying from the dry limestone forest of Portland Ridge to a red mangrove (Rhizophora mangle) swamp to roost. The next evening we saw 86 Plain Pigeons and large numbers of White-crowned Pigeons flying to the mangrove roost. We hypothesized that the use of the forest by columbids was a seasonal response to increased fruit availability, since many trees in Portland Ridge’s dry forest produce ripe fruit during the dry season. In this paper, we document the seasonal use of a threatened Caribbean dry forest by Plain and White-crowned pigeons and examine their abundance in relation to the fruiting phenology of Thrinax parviflora, a common dry season fruiting species. 74 THE WILSON BULLETIN • Vol. 113, No. 1, March 2001 TABLE 1. Mean counts (6 S.E.) of fruits from 10 Thrinax parviflora trees and evening counts of columbids flying from the Portland Ridge dry forest to a mangrove roost site during the 1996–1997 dry season. Fruit counts and columbid counts were conducted within 2 days of each other.