BREEDING ECOLOGY OF THE PUAIOHI (

We studied the breeding ecology of the critically endangered Puaiohi ( Myadestes palmeri), a poorly known Hawaiian thrush endemic to the island of Kauai. From 1996 through 1998, we monitored 96 active nests over the course of three breeding seasons. Mean clutch size was 2.0, and pairs produced an average of 1.5 fledglings/successful nest. Pairs renested after failure and some raised multiple broods. The mean annual reproductive effort was 2.1 nesting attempts/territory, and pairs produced a mean 1.1 fledglings/attempt. Large differences in nesting effort and productivity occurred among years, with mean number of fledglings/territory ranging from 0.4 to 4.9. Predation by owls (probably Short-eared Owls, Asio flammeus) and introduced rats (probably black rats, Rattus rattus) accounted for most nest failures. The presence of non-breeding floaters in the population and their largely unsuccessful attempts to gain territories in the study area suggest that the population is near carrying capacity. The high reproductive potential of the Puaiohi may help explain its per- sistence despite the species' historical rarity. Received 29 April 2004, accepted 22 November 2004. The Puaiohi (Myadestes palmeri) is a rare and poorly known thrush restricted to forests above 1,000 m elevation on the island of Kau- ai in the Hawaiian Islands. Of the five Ha- waiian thrushes, it is the most divergent vo- cally, morphologically, and behaviorally (Pratt 1982). Except for the Omao (M. obscurus )o n the island of Hawaii, the other species are considered critically endangered or extinct (Collar et al. 1994, Reynolds and Snetsinger 2001). Intensive efforts over the last 4 decades to document the status of Hawaii's forest birds suggested that the Puaiohi was exceedingly rare and had experienced a range contraction since the 1960s (Sincock et al. 1984, Scott et al. 1986, Pyle 1994). In the course of these studies, a number of factors were implicated in the loss of Hawaii's forest bird populations. It is thought that habitat modification, avian disease, competition, and predation have acted in concert to diminish available habitat and