The breeding ecology of the Amakihi (Loxops virens) and Palila (Psittirostra bailleui) on Mauna Kea, Hawaii

Author:

Van Riper, Charles

Title:

The breeding ecology of the Amakihi (Loxops virens) and Palila (Psittirostra bailleui) on Mauna Kea, Hawaii

Periodical:

Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Zoology ; no. 1128

Year:

1978

Volume:

Ph.D.

Pages:

xiii, 166 leaves

Subject:

Loxops virens Psittirostra bailleui Drepanididae Birds Hawaii Island

Summary:

The behavioral ecology and breeding biology of the Amakihi and Palila, two members of the endemic Hawaiian honeycreeper family (Drepanididae) were studied on Mauna Kea, Hawaii, from 1971 to 1975. Birds were color-banded. Aspects of the environment (forest structures and phenology, weather, and mammalian predators) were monitored. The bird populations on Mauna Kea consisted of resident adults that each year returned to the same areas to breed, juveniles that rarely bred in their first year, and an excess of unmated males. Most intense breeding in the Amakihi occurred from March to May, the period of most abundant mamane flowering, while the most intense period of Palila breeding was from June to August, the time of maximum mamane fruit production. The Palila used green mamane pods as a primary food source while Amakihi took mamane nectar and insects. Because of high population numbers in relation to available nectar (and possibly insects), the Amakihi appeared resource limited. Amakihi, and possibly Palila, retain mates for more than one season. During breeding Palila males defended an area around their mate whereas Amakihi territory was a fixed location that encompassed the nest site and all food. Amakihi territory size and location were related to available food resources (insects and nectar). Nests of both species were open cups and both laid eggs of similar coloration. Palila clutch size was most commonly two, and in the Amakihi averaged 2.5 eggs. Clutch size was important as a productivity regulator only in the Amakihi, in that it varied between years such that, in a year of low food availability, birds with clutch sizes of two actually fledged more young than those with 3-egg clutches. Incubation periods were about 14 and 16 days for the Amakihi and Palila, respectively. Clutches hatched asynchronously and this was suggested as being a possible mechanism of brood reduction. Amakihi nestling period averaged 17 days while Palila took 22-23 days to fledge. These periods are long compared to other passerines. Both parents fed the young but only the female incubated and brooded. Population productivity was much higher in Amakihi than Palila, partially due to the already low numbers of Palila and its longer nesting cycle. It was determined that Palila could potentially raise only one set of young while Amakihi did raise two in a season. Some suggestions as to why the Palila is rare included a more specialized niche, destruction of habitat, and possible predation pressure (predatory mammals included a high proportion of birds in their diet). Based on behavioral ecology and biology of the Amakihi and Palila, in addition to recent anatomical evidence, it was concluded that Drepanididae are closely aligned with the Carduelinae and probably arose from a primitive member of that subfamily. The finch-billed drepanidids appear to somewhat separated from the rest of the family, and it is suggested they assume subfamily status.

Collection:

Monographs