Steven G. Fancy

Temporal variation in bird counts within a hawaiian rainforest

Abstract 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 significativas en las estimaciones de densidad entre meses y años. Tres nectarívoros nativos presentaron estimaciones de densidad mayores durante sus épocas reproductivas (diciembre–mayo) y mostraron disminuciones durante períodos de baja producción de néctar luego de la estación de cría. Excepto una, todas las especies insectívoras y generalistas presentaron mayores estimaciones de densidad durante sus épocas reproductivas (marzo–agosto). Las estimaciones de densidad de todas las especies también variaron con la altitud, y se encontraron cambios estacionales en las poblaciones de cuatro especies. Nuestros datos muestran que el mejor momento para realizar conteos de aves nativas de selva en Maui es enero–febrero, cuando las aves están criando o preparándose para criar, los conteos son típicamente altos, la variabilidad en las estimaciones de densidad es baja y la probabilidad de buen tiempo es más alta. La variación temporal en las estimaciones de densidad documentadas en nuestro sitio de estudio enfatizan la necesidad de regímenes de muestreo consistentes y bien establecidos, y sugiere cautela a la hora de sacar conclusiones para conservación o tomar decisiones de manejo a partir de datos de muestreos.

Population structure and survival of Palila

Annual survival, age, and sex ratios of the endangered Palila (Loxioides bailleui) on Mauna Kea, Hawaii, were determined from multiple captures and resightings of 984 individuals during 1987-1993. The proportion of Second Year (SY) Palila in the population was relatively constant among years, whereas the proportion of Hatching Year (HY) birds ranged from 3.1 to 22.6% over three years. Sex ratios of nestling and SY Palila did not differ from unity, but the sex ratio of HY and ASY Palila was male-biased. Mean proportion of adult males was 63. ± 1.8 SE, and males outnumbered females in all six years of the study. Mean annual survival of HY Palila (0.36 ± 0.08) was lower than that of After Hatching Year (AHY) birds (0.63 ± 0.05), but annual survival of AHY males (0.65 ± 0.07) did not differ from that of AHY females (0.62 ± 0.06). Survival was negatively correlated with annual changes in the availability of green mamane (Sophora chrysophylla) pods, the primary food of Palila. The skewed adult sex ratio may result from greater emigration or mortality of HY females, or from greater mortality of breeding females due to increased exposure to predation

DESCRIPTION OF NESTS, EGGS, AND NESTLINGS OF THE ENDANGERED NIGHTINGALE REED-WARBLER ON SAIPAN, MICRONESIA

Abstract We describe the first verified nests, eggs, and nestlings of the Nightingale Reed-Warbler (Acrocephalus luscinia), an endangered species endemic to the Mariana Islands, Micronesia. Nest composition, nest dimensions, and eggs were studied on the island of Saipan. Nests were located within three habitat types: upland introduced tangantangan (Leucaena leucocephala) forest, a native mangrove (Bruguiera gymnorrhiza) wetland, and a native reed (Phragmites karka) wetland. Nesting substrates included five native and two introduced tree species and one native reed species. Nests were composed primarily of dry vine stems, needle-like branchlets of ironwood (Casuarina equisetifolia), and tangantangan petioles. Nests were compact to bulky in construction and were secured to a forked arrangement of branches or stems. The background color of eggs ranged from white to cream to ivory-buff. Eggs were spotted, speckled, and blotched with gray, brown, black, and rust colored markings. Clutch size was 2–4, with a mode of two. Hatchlings were altricial with closed eyelids and devoid of natal down with dark gray to black skin. Nestlings examined prior to fledging resembled the adult plumage, except for the lack of the yellow supercilium found in adults. The nests and eggs have some characteristics similar to those of other Acrocephaline warblers found throughout Micronesia and Polynesia.