Long term ecological studies are valuable for detecting changes over time. We compared forest composition and Hawai‘i ‘elepaio (Chasiempis sandwichensis) nest site selection over a 25-year period in Hawai‘i Volcanoes National Park (HAVO). Hawai‘i ‘elepaio are a species of monarch flycatcher (Family: Monarchidae) that are endemic to the Big Island of Hawai‘i. In 1993–1994, Sarr et al. (1995) studied Hawai‘i ‘elepaio nest site selection and forest structure in mesic montane forest recovering from ungulate damage along Mauna Loa Road in HAVO. In 2016, we used the same location and methods to compare ‘elepaio nest site selection by recording nest placement with respect to tree species, tree height, nest height, and nest tree DBH. In 1993-1994 Sarr et al. used a point-center-quarter method to quantify forest composition including tree density, tree relative abundance, tree height, and DBH, and we repeated these methods in the same plot in 2019. The study area is located at approximately 1,800 m.a.s.l. and is dominated by three tree species: a‘ali‘i (Dodonaea viscosa), koa (Acacia koa), and māmane (Sophora chrysophylla).
Results/Conclusions
Our measurements suggest that heights of nests and nest trees were greater for a‘ali‘i and koa in the earlier study, but DBH of non-nest trees trended upward for both species over time. Twice as many ‘elepaio nests were found in a‘ali‘i as in koa in both time periods. Overall tree density was 0.16 trees/m2 earlier and 0.26 trees/m2 later. Koa density was 0.09 trees/m2 earlier and 0.11 trees/m2 later, and a‘ali‘i density was 0.08 trees/m2 earlier and 0.12 trees/m2 later. The density of māmane was 0 trees/m2 earlier but was 0.02 trees/m2 in 2016. Koa relative abundance was 53% earlier and 45% later, but a‘ali‘i remained constant at 47% over time. The relative abundance of māmane was not recorded earlier but was 8% in 2016. We found that both forest composition and ‘elepaio nest tree characteristics changed over time, suggesting a response to habitat restoration efforts. Our results suggest that changes in forest structure may affect nesting behavior, but in ways that are not necessarily simple or consistent.