TEMPORAL VARIATION IN BIRD COUNTS WITHIN A HAWAIIAN RAINFOREST

We studied monthly and annual variation in density estimates of nine forest bird species along an elevational gradient in an east Maui rainforest. We conducted monthly variable circular-plot counts for 36 consecutive months along transects running downhill from timberline. Density estimates were compared by month, year, and station for all resident bird species with sizeable populations, including four native nectarivores, two native insectivores, a non-native insectivore, and two non-native generalists. We compared densities among three elevational strata and between breeding and nonbreeding seasons. All species showed significant differences in density estimates among months and years. Three native nectarivores had higher density estimates within their breeding season (December–May) and showed decreases during periods of low nectar production following the breeding season. All insectivore and generalist species except one had higher density estimates within their March–August breeding season. Density estimates also varied with elevation for all species, and for four species a seasonal shift in population was indicated. Our data show that the best time to conduct counts for native forest birds on Maui is January–February, when birds are breeding or preparing to breed, counts are typically high, variability in density estimates is low, and the likelihood for fair weather is best. Temporal variations in density estimates documented in our study site emphasize the need for consistent, well-researched survey regimens and for caution when drawing conclusions from, or basing management decisions on, survey data. Variación Temporal en Conteos de Aves en una Selva Lluviosa de Hawai Resumen. Estudiamos la variación mensual y anual en estimaciones de la densidad de nueve especies de aves a lo largo de un gradiente altitudinal en una selva lluviosa del este de Maui. Realizamos conteos mensuales en parcelas circulares por un período de 36 meses consecutivos a lo largo de transectas ubicadas desde la línea del bosque hacia abajo. Las estimaciones de densidad fueron comparadas entre meses, años y estaciones considerando todas las especies de aves residentes con poblaciones considerables, incluyendo cuatro nectarívoros nativos, dos insectívoros nativos, un insectívoro no nativo y dos generalistas no nativos. Comparamos densidades entre tres estratos altitudinales y entre las estaciones reproductivas y no reproductivas. Todas las especies mostraron diferencias significat