Distribution, abundance, and acoustic characteristics of Kohala forest birds













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Kohala, the northernmost volcano out of the five that comprise Hawai’i Island, is home to the most spatially isolated population of Hawaiian forest birds on the island. The avian community on Kohala is one of the few native bird populations in the state that has not been monitored since the landmark Hawai’i Forest Bird Survey (HFBS) in 1979. Here, I examine changes in the distribution and abundance of forest birds on Kohala since 1979. I surveyed 143 stations across 13 transects in Pu’u ‘O ‘Umi Natural Area Reserve in Kohala from March through May 2017 and incorporated the 1979 HFBS data from 80 stations across 3 transects that occurred in our study site. I detected 2806 individuals of 15 different species across the 143 survey stations and observed changes in species densities ranging from -8.4% (C. sandwichensis) to +714% (D. coccinea). While equivalence testing showed meaningful increases in population densities for all but one species, changes in survey protocol standards may have limited our ability to make direct comparisons with the HFBS. I also document here the introduction and establishment of C. diphone in Kohala. Populations that are isolated have a high potential to diverge acoustically. As forest birds use song primarily to defend territory and attract mates, major changes in the acoustic properties of song can reinforce reproductive isolation, leading to assortative mating and speciation. While some native species like the Hawai’i ‘amakihi have demonstrated an evolved tolerance to avian malaria and begun to repopulate low-elevation habitats and reconnect populations, it is unclear the level to which song divergence has already reinforced reproductive isolation. To address this question, I examined how long-term isolation has affected the song diversity and acoustic traits of the Kohala population of the Hawai’i ‘amakihi compared to the geographically-nearest four populations. I recorded and analyzed 7,183 ‘amakihi songs across all five populations from 2013 to 2017, with a total of 57 unique song types. I found significant variability in song types among all five populations and relatively uniform variation within populations. Principal component analysis of temporal and frequency measurements revealed that the Kohala population is unique in its acoustic characteristics. Future behavioral assays can indicate whether this uniqueness has reinforced reproductive isolation in Kohala ‘amakihi over larger time scales.



Conservation biology, Acoustics, Demography, Abundance, Bioacoustics, Density, Forest birds, Hawai'i



44 pages


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