Director UCSC Doris Duke Conservations Scholar Program, United States
Abstract: Islands are extinction epicenters, with 75% of all extinctions and 95% of all bird extinctions occurring on islands. Madagascar, home to 117 endemic bird species, is highly susceptible to extinctions. Forests in Madagascar host 90.5% of all endemic passerine birds. In spring 1996 and 2021, we conducted floral and faunal inventories of the southeastern slopes of the Marojejy Massif eastern humid forest, within Parc national de Marojejy, resurveying sites sampled as early as January 1952. Understanding shifts over time in the elevational distribution of forest bird species in Parc national de Marojejy may help uncover changes in the environment, allowing for human intervention that helps reduce species extinction. At each site, we conducted point counts, mist-netting, and playback surveys across microhabitats to maximize species detection. We assigned birds into groups by feeding guild and diet (sally-gleaner, understory insectivore, opportunistic insectivore, animalivore, frugivore, nectarivore, and
granivore; gastropods, insects and arthropods, vertebrates, nectar, fruit, and/or seeds).
In total, 91 bird species were detected between 1996 and 2021. Further, 39 species were captured via mist-netting, and 52 species were only detected from direct observation (visual or aural). Three-quarters of sally-gleaners and/or understory insectivorous birds detected are considered to have a low tolerance to forest habitat degradation, the lowest tolerance to forest habitat degradation of the three feeding behavior groups. Sally-gleaning and/or understory insectivorous feeding species had a range of elevational distributional shifts between 1996 and 2021: increase (33.3%), decrease (30.3%), or no change (36.4%). Among those that increased or decreased elevation, 73.9% are species considered susceptible to forest habitat degradation and made up the majority of species that shifted elevational distribution. When comparing a less specialized feeder group, almost half of opportunistic insectivores and animalivores showed no shifts in elevational distribution, and only 33.2% of those species are susceptible to forest habitat degradation. These findings support the hypothesis that as the dry season lengthens in Parc national de Marojejy, the elevational distribution range of sally-gleaners and insectivorous understory birds widened between 1996 and 2021, especially amongst low-tolerance species: insectivorous bird species with more specialized feeding behaviors such as sally-gleaning or feeding in the dense understory have more marked changes in elevational distribution. Changes in island avian elevational distribution of birds based on the specialization of foraging behavior may be an indicator of the mechanistic impacts of climate change on island ecosystems.
