SummaryFrugivorous White-ruffed ManakinsCorapipo leucorrhoa(Pipridae) showed pro nounced seasonal emigration from a pre-montane wet forest site (550 m) on the Atlantic slope of Costa Rica. “Resident” breeders left the area between August and October, and returned between February and April, at the onset of the breeding season. Female patterns differed from those of males primarily in later departure (October) and later return (April). I documented 57 fruit species in the diet at this locality and monitored phenology for 43 of those species, many of which were understorey members of the Melastomataceae. The emigration did not coincide with a period of local fruit shortage (relative to abundance at the same locality in other months), but the relative abundance and species composition of fruit resources in the areas to which the manakins migrated remains unknown. However, peak resources did coincide with the period in which recent fledglings would be commonest and the period during which most individuals were moulting prior ot emigration. Resources were lowest from November, when residents were absent, untilJune, well into the breeding season. Tentative evidence suggests considerable annual variation, possibly owing to differences in the timing of the rainy season. Individuals captured during the period when almost all “resident” breeders were absent (November) appeared to be transients, and were rarely recaptured. Weights differed between sexes, with females (χ = 12.5 ± 1.0) significantly heavier than males (χ = 11.1 ± 0.8). Males were lightest during the breeding season, intermediate in weight during the moulting period, and both sexes were heaviest during the migration period, when they accumulated subcutaneous fat. Females were lightest during the moult period, at which time many may also have dependent fledglings. Many other frugivores and nectarivores may engage in similar altitudinal migrations. Even where altitudinal migration is not possible, birds might migrate to other habitats with different fruit resources or phenologies. The design of nature reserves should accommodate the possibility of significant altitudinal (or cross-habitat) migration for many species of frugivores and nectarivores.
Evolution of altitudinal migration in passerines is linked to diet