Diverse habitat use during two life stages of the critically endangered Bahama Oriole (Icterus northropi): community structure, foraging, and social interactions

Abstract

Our ability to prevent extinction in declining populations often depends on effective management of habitats that are disturbed through wildfire, logging, agriculture, or development. In these disturbed landscapes, the juxtaposition of multiple habitat types can be especially important to fledglings and young birds, which may leave breeding grounds in human-altered habitat for different habitats nearby that provide increased foraging opportunities, reduced competition, and higher protection from predators. In this study, we evaluated the importance of three habitat types to two life stages of the critically endangered Bahama Oriole (Icterus northropi), a synanthropic songbird endemic to Andros, The Bahamas. First, we determined the avian species composition and relative abundance of I. northropi among three major vegetation types on Andros: Caribbean pine (Pinus caribaea) forest, coppice (broadleaf dry forest), and anthropogenic areas, dominated by nonnative vegetation (farmland and developed land). We then compared the foraging strategies and social interactions of two age classes of adult Bahama Orioles in relation to differential habitat use. Bird surveys late in the Bahama Oriole’s breeding season indicated the number of avian species and Bahama Oriole density were highest in coppice. Some bird species occurring in the coppice and pine forest were never observed in agricultural or residential areas, and may be at risk if human disturbance of pine forest and coppice increases, as is occurring at a rapid pace on Andros. During the breeding season, second-year (SY) adult Bahama Orioles foraged in all vegetation types, whereas after-second-year (ASY) adults were observed foraging only in anthropogenic areas, where the species nested largely in introduced coconut palms (Cocos nucifera). Additionally, SY adults foraging in anthropogenic areas were often observed with an ASY adult, suggesting divergent habitat use for younger, unpaired birds. Other aspects of foraging (vegetation features, food-gleaning behavior, and food items) were similar for the two age classes. Older Bahama Orioles exhibited relatively higher rates of social interactions (intraspecific and interspecific pooled) in anthropogenic areas, and won more interaction outcomes compared to younger adults. Our findings concur with those of other studies indicating dry broadleaf forest is vitally important to migrating, wintering, and resident birds, including the critically endangered Bahama Oriole, which appears to depend heavily on this vegetation type during certain life stages.

Hierarchical distance sampling reveals increased population size and broader habitat use in the endangered Bahama Oriole

“…These species may have suffered declines due to some of the same threats that face the Bahama Oriole, including cowbird parasitism (Lovette et al 1999). Although Shiny Cowbirds have been observed on Andros (Baltz 1996) and have been recorded parasitizing Bahama Oriole nests in anthropogenic habitats (Price et al 2011;KEO, unpublished data), cowbird observations in other habitats remain sparse (Price and Hayes 2017;KEO, unpublished data).…”

“…One survey conducted in February 2002 found orioles in moderate densities in mixed pine/coppice and low densities in pure coppice but did not report any orioles in pure pine forest (Currie et al 2005). A survey conducted in July 2005 found that the orioles use both coppice and pine habitats but suggested that they occur in higher density in coppice (Price and Hayes 2017).…”

Nest site characteristics of the Critically Endangered Bahama Oriole (<em>Icterus northropi</em>)

“…Our study focused on the pine forests in North Andros (Fig. 1), which were logged heavily in the mid-1900s (Henry 1974, Price andHayes 2017). The pine forest vegetation includes Caribbean pines and an understory of Key thatch palms, poisonwood (Metopium toxiferum), ferns, and other broadleaf shrubs (Stonko et al 2018).…”

“…In developed areas on Andros, many coconut palms (Cocos nucifera), an important nest tree for Bahama Orioles along the settled east coast, have been killed by lethal yellowing disease (Price et al 2015). Logging and residential development have caused the orioles to lose native pine forest habitat as well (Price and Hayes 2017).…”