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 63.7% ± 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.