The effect of isolation, fragmentation, and population bottlenecks on song structure of a Hawaiian honeycreeper

Abstract

Little is known about how important social behaviors such as song vary within and among populations for any of the endemic Hawaiian honeycreepers. Habitat loss and non‐native diseases (e.g., avian malaria) have resulted in isolation and fragmentation of Hawaiian honeycreepers within primarily high elevation forests. In this study, we examined how isolation of Hawai'i ‘amakihi (Chlorodrepanis virens) populations within a fragmented landscape influences acoustic variability in song. In the last decade, small, isolated populations of disease tolerant ‘amakihi have been found within low elevation forests, allowing us to record ‘amakihi songs across a large elevational gradient (10–1800 m) that parallels disease susceptibility on Hawai'i island. To understand underlying differences among populations, we examined the role of geographic distance, elevation, and habitat structure on acoustic characteristics of ‘amakihi songs. We found that the acoustic characteristics of ‘amakihi songs and song‐type repertoires varied most strongly across an elevational gradient. Differences in ‘amakihi song types were primarily driven by less complex songs (e.g., fewer frequency changes, shorter songs) of individuals recorded at low elevation sites compared to mid and high elevation populations. The reduced complexity of ‘amakihi songs at low elevation sites is most likely shaped by the effects of habitat fragmentation and a disease‐driven population bottleneck associated with avian malaria, and maintained through isolation, localized song learning and sharing, and cultural drift. These results highlight how a non‐native disease through its influence on population demographics may have also indirectly played a role in shaping the acoustic characteristics of a species.

Archaic Dialect of Chaffinch, Fringilla coelebs (Passeriformes, Fringillidae), Song in the Lower-Dnipro Area (South Ukraine) and Its Territorial Relations

“…It is possible because local population of "native speakers" was numerous all the time of dialect existence. Otherwise, the song diversity declines (Pang-Ching et al, 2018;Paxton et al, 2019), and the number of songs would be incomparably lesser than in other dialects.…”

Anticipated effects of abiotic environmental change on intraspecific social interactions

“…Therefore, the alteration of habitat structure can influence both the structure of acoustic signals as well as the reliability of acoustic communication (reviewed in Rabin & Greene, 2002). For example, the songs of Hawai'i 'amakihi birds (Chlorodrepanis virens) in less-complex habitats have more energy at higher frequencies than songs in closed habitats (Pang-Ching et al, 2018). Observational comparisons of black-capped chickadees found that birds in disturbed habitats have reduced signal reliability and can likely hear fewer other males compared to chickadees living in highquality old-growth habitat (Hansen et al, 2005).…”

Loss of cultural song diversity and the convergence of songs in a declining Hawaiian forest bird community

“…If current rates of decline for Kaua‘i honeycreepers continue, multiple extinctions are predicted in the coming decades [31]. Based on field observations of apparent increasing similarity in song among Kaua‘i honeycreeper species, we hypothesized that rapid declines in the density and distribution of Kaua‘i honeycreepers could have resulted in the loss of complexity and diversity within species' present-day songs [33] due to the lower number of individuals from which young birds can learn, resulting in an increase in similarity among species’ present-day songs. We examined acoustic characteristics of songs recorded during three time periods (1970s, early 2000s, present day) for three species of honeycreepers: ‘akeke‘e ( Loxops caeruleirostris ), ‘anianiau ( Magumma parva ) and Kaua‘i ‘amakihi ( Chlorodrepanis stejnegeri ).…”

“…If current rates of decline for Kaua'i honeycreepers continue, multiple extinctions are predicted in the coming decades [31]. Based on field observations of apparent increasing similarity in song among Kaua'i honeycreeper species, we hypothesized that rapid declines in the density and distribution of Kaua'i honeycreepers could have resulted in the loss of complexity and diversity within species' present-day songs [33] due to the lower number of individuals from which young birds can royalsocietypublishing.org/journal/rsos R. Soc. open sci.…”