Foraging Behavior of the Acorn Woodpecker in Belize, Central America

-The foraging behavior of the Acorn Woodpecker (Melanerpes formicivorus) was observed during the dry season in the Pine Ridge region of Belize. The birds ate a variety of foods commonly consumed by this species in temperate regions, including flying insects, oak sap, and insects obtained by surface gleaning and probing. All birds also stored large numbers of acorns in natural cavities and in woodpecker-modified holes. The woodpeckers' social organization here resembled that found in most temperate habitats. All of the birds observed lived in stable social groups that contained between two and six individuals. No solitary birds were recorded. Although nesting was not studied, it is likely that the birds breed communally in Belize as elsewhere in their range. The Acorn Woodpecker (Melanerpes formicivorus) is a common resident of oak and pine-oak woodlands from western North America southward through Central America to northern Colombia (Ridgway 1914). In temperate habitats, most individuals live in year-round groups that collectively harvest and store acorns as a winter food supply (Bent 1939). The foraging ecology of this species has been examined extensively in North America (Ritter 1929, Bent 1939, MacRoberts 1970, Roberts 1979), but has not been studied in detail elsewhere. The Acorn Woodpecker has been reported to occur in association with oaks throughout Central America and Colombia, yet considerable variation may exist in the extent to which acorns are utilized and/or stored in modified holes. For example, neither Dickey and Van Rossem (1938) in El Salvador, nor Ridgely and Gaulin (1980) in Colombia, found any evidence that this species stored or even fed on the acorns that were present at their respective study areas. Skutch (1969) reported that the Acorn Woodpeckers which he had observed in various parts of Central America did frequently feed on acorns, but that they stored the nuts in natural crevices in the bark of trees and not in individual storage holes. However, he published a photograph of a storage tree that had been found in Honduras, and both Peck (1921) and Russell (1964) reported that this species made storage holes in dead pines (Pinus spp.) in Belize (British Honduras). I examined the foraging behavior of Acorn Woodpeckers during the dry season in a tropical dry forest in Belize. I wished to determine whether or not the birds used acorns in this habitat, the extent to which the nuts were stored, and the relative importance of acorns as a food source. I also studied the social organization of the woodpeckers to determine whether the birds' behavior in this environment differed from that of North American populations studied previously by MacRoberts and MacRoberts (1976), St cey (1979), Koenig (in press) and others. STUDY AREA AND METHODS My study area was in the Pine Ridge region of Belize, approximately 28 km west of Belize City near the Western Highway. The Pine Ridge is a coastal pineoak savanna, characterized by gently sloping ridges and a well-drained sandy clay soil. The common trees in this association include Caribbean pine (Pinus caribaea), oaks (Quercus oleoides and two unidentified species), craboo (Byrsonima crassifolia) and palmetto (Acoelorraphe wrightii). Various sedges (Rhynchospora spp.) predominate in open areas. Patches of hardwood forests occur near the banks of several small streams that ran through the study area. These small forests contain many scrubby second growth species as well as larger trees typical of limestone soils throughou the lowland areas of Belize (see Wright et al. 1959, Russell 1964). I studied Acorn Woodpeckers during 240 observerhours between 15 February and 6 March 1977. The dry season in Belize normally occurs between February and May. Although rainfall records were not available at the study area, Belize City receives only about 10% of its annual rainfall (185 cm) during the dry season (Russell 1964). I observed the foraging behavior primarily of three groups, obtaining additional data from five other groups in the vicinity. I watched each group during various times of the day, and, where possible, followed individual birds as they moved through their territories. Foraging behavior was divided into six categories described below. An individual was scored as having performed a feeding pattern each time it changed from one bout of a behavior to another bout of the same or different behavior (e.g., Cruz 1977). For example, if a woodpecker was gleaning for insects, it was considered to have made one gleaning bout each time it left one tree and flew to a new tree. Sap eating was also scored in bouts: i.e., each time an individual fed on sap at one site in a particular tree, rather than