| Hawaiian forest birds have become imperiled by anthropogenic factors since the arrival of the first humans circa 400 A.D. Threats such as habitat alteration due to urban and agricultural development, introduced disease, and forest invasion by introduced mammals have contributed to declines in bird communities have made Hawai'i home to one-third of endangered species in the United States. Two endemics to Kaua'i, the 'Akikiki (Oreomystis bairdi) and 'Akeke'e (Loxops caeruleirostris), are the most recent Hawaiian birds added under the Endangered Species Act. Due to funding constraints and the inaccessibility of forest bird habitat, the breeding biology of these species was poorly known prior to this study. Because vital rates, such as reproductive success and survival, are important parameters to assess when managing a species, I conducted the first comprehensive breeding biology study of 'Akikiki and 'Akeke'e to determine if recent population declines of these species were due to low nesting success. I also conducted a larger study to investigate factors that affect nesting success of native, arboreal nesting songbirds on Kaua'i to assess the nesting success of the community as a whole, providing additional context for my results on 'Akikiki and 'Akeke'e. The larger study included four additional species, and investigated the importance of rodent predators, and other factors, on Kaua'i forest bird nesting success. I searched for and monitored nests in the Alaka'i Wilderness from March-June of 2012 and 2013, and used program MARK to generate estimates of nesting success based on exposure days. I used the generalized linear model framework in MARK to build competing a priori models that incorporated variables such as time, nest height, nest age, and species. Results showed that 'Akikiki and 'Akeke'e had high nesting success (0.77 +/- 0.12 and 0.71 +/- 0.17 SE, respectively) relative to other birds at my site (57 +/- 0.05 SE overall), and relative to the mean estimate of nesting success based on a meta-analysis of Hawaiian forest bird nest studies (0.46). Nest predation was not a major cause of nest failure for the endangered species, but it was attributed to at least 40% of failures in my larger study. Cause of failure could not be determined for about half of nest failures. Time was the only variable in my models that had substantial influence on daily survival rates of nests. Nesting success was higher in 2013 than in 2012, and decreased in the middle of the breeding season (beta = 0.001 +/- 0.0004 SE, wi = 0.33). The major findings of my study were: 1) nesting success was apparently not an important cause of decline for 'Akikiki and 'Akeke'e, and future studies of these species should focus on assessing juvenile and adult survival rates, in addition to threats that might affect these rate, such as habitat quality and disease; and 2) nesting success varied across the breeding season for the native forest birds in my system. Because causes of failure were often difficult to assess due to extreme nest heights or lack of evidence to suggest weather or predation, future studies would benefit from using methodology that allows for more effective nest monitoring (i.e. nest cameras). |
