Rusty Blackbirds select areas of greater habitat complexity during stopover

Abstract

ABSTRACT The Rusty Blackbird (Euphagus carolinus) is a widespread, uncommon migrant that has experienced heavy population declines over the last century. This species can spend over a quarter of their annual cycle on migration, so it is important to determine their habitat requirements during stopover events to inform effective conservation planning. We assessed their habitat selection at an important stopover site in northern Ohio during both fall and spring migration. Since stopover habitat selection is scale-dependent, we investigated both patch-scale (between patches) and fine-scale (within a patch) selection using radio telemetry to locate foraging and roosting flocks, and compared habitat variables between used and available points across the study site. At the patch scale, we found that birds preferred dogwood–willow swamp, low-lying forest patches, and areas of greater habitat complexity for foraging in both seasons. At the fine scale, spring migrants foraged closer to habitat edges than random, and preferred areas with more wet leaf litter and shallow water, and less grass cover. Fall migrants also preferred shallow water and leaf litter cover, and avoided areas with dense grass, forbs, and herbaceous shrub cover. By contrast, birds consistently roosted in dense stands of emergent Phragmites or Typha marsh, suggesting that the best stopover or staging sites are those with a matrix of different wetland habitats. Although the migratory range of Rusty Blackbirds is currently dominated by agricultural development, our results suggest that fragmented landscapes can still provide adequate habitat for migrants if the available land is managed for a variety of wet habitat types. LAY SUMMARY The Rusty Blackbird is a widespread, uncommon migrant that has experienced heavy population declines over the last century. Rusty Blackbirds can spend over a quarter of the year on migration, so it is important to determine their habitat requirements during stopover events to inform conservation planning. We assessed their habitat selection at 2 spatial scales at an important stopover site in Ohio during fall and spring migration, using radio telemetry to locate foraging and roosting flocks. At the patch scale, we found that Rusty Blackbirds preferred dogwood–willow swamp, flooded forest patches, and areas of habitat complexity for foraging. At the fine scale, birds foraged close to habitat edges, and preferred areas with more wet leaf litter and shallow water, while avoiding dense grass, forbs, and herbaceous shrub cover. By contrast, Rusty Blackbirds consistently roosted in dense stands of emergent marsh, suggesting that the best stopover sites are those with several different wetland habitats.