Use of Shrub Habitats by Fall Birds at Iroquois National Wildlife Refuge, Alabama, New York

Abstract

Many studies have suggested that early successional habitats are important for fall migrants and resident birds. In light of this, I studied birds at Iroquois National Wildlife Refuge, Alabama NY, to determine habitat relationships, fruit consumption, and utility of transects and mist nets for counting birds in early successional habitats during the fall. I used transects to count birds in 18 sites (12 shrub and six forest) during the fall in 2008 and 2009, and collected habitat data to construct habitat models. I examined frugivory of fall birds by employing a paired open/enclosed fruit branch method and by analyzing fecal samples. I also sampled birds using mist nets and transects simultaneously to determine if the two methods yield similar estimates of bird abundance. More birds were detected in shrub lands than in forests across the two years. Total bird abundance was affected positively by fruiting species richness and negatively by small stem abundance. American Robin (Turdus migratorius) abundance was positively related to total shrub cover and common buckthorn (Rhamnus cathartica) fruit abundance, and negatively related to both small and large stem abundance. Gray Catbird (Dumetella carolinensis) abundance was positively related to fruiting shrub species richness. Song Sparrow (Melospiza melodia) abundance was positively related to gray dogwood (Cornus racemosa) fruit abundance, and negatively related to small stem abundance and bella honeysuckle (Lonicera X bella) fruit abundance. Birds as a whole consumed fruit disproportionately relative to availability, consuming more bella honeysuckle and common buckthorn than gray dogwood. Fruits disappeared from open shrub branches significantly faster than netted branches, suggesting frugivory occurred. Mist nets detected a greater species richness than transects in all fields and years. Correlations between mist net and transect bird abundances were mixed, with significant positive relationships for larger, noisy species such as Gray Catbirds, American Robins, and Song Sparrows, but not for small, cryptic species. My results suggest shrublands that contain fall fruiting shrub species are the best habitats to manage for fall birds. Also, transects are an adequate method of sampling fall birds in early successional habitats given several important qualifiers related to detectability.