Juvenile Dispersal and Adult Home Range size of an Endangered Hawaiian Honeycreeper, the Akohekohe (Palmeria dolei)

Alex Wang (UH-Hilo)
Dr. Patrick Hart (UH-Hilo)
Dr. Eben Paxton (USGS)
Dr. Ryan Perroy (UH-Hilo)

The Akohekohe (Palmeria dolei) is endemic to the island of Maui, Hawaii, and remains critically endangered despite decades of habitat restoration efforts.  This species is long-lived (>12 yr), has high adult annual survival (0.95 ± 0.10 [SE]) and relatively high nest success (68% by Mayfield method) but is extremely vulnerable to avian malaria spread by mosquitoes.  This limits the Akohekohe to high elevation, mosquito-free refugia that disease modelling suggests occurs above 1715 m in elevation.  It has been hypothesized that in summer, the nectarivorous Akohekohe follows seasonal flower blooms of the dominant canopy tree, ohia (Metrosideros polymorpha), to lower elevations where they experience increased mortality from malaria and that this mainly occurs in juvenile birds.  To examine this hypothesis, I have been examining movement patterns of adult (n=24) and juvenile (n=11) Akohekohe using radio-telemetry. I have found that the size of adult and juvenile home ranges are significantly different (W=5, p<0.001).  Adult Akohekohe are highly philopatric with relatively small home ranges (0.53 ha ± 0.07 [SE]), whereas juveniles travel more extensively and are more variable in their movement behavior (25.93 ha ± 7.89).  The propensity for juvenile birds to range more widely likely increases their exposure to disease.  Furthermore, only juvenile but not adult birds were found below the elevation that modeling suggests can support avian malaria seasonally in summer and fall.  The absence of adult home ranges in this transitional malaria zone suggests that Akohekohe cannot persist throughout the year at these elevations.  Population estimates for this species have remained stable for the past 30+ years and this research may indicate that it is juvenile dispersal that could be the population-limiting mechanism for this endangered species.