Arthropod communities associated with habitats occupied by breeding Swainson's Warblers

Abstract

The Swainson's Warbler (Limnothlypis swainsonii) is an insectivorous songbird and a species of conservation concern in the southeastern U.S. Because it is specialized for foraging in the litter of the forest floor, it is dependent on a well-developed leaf-litter layer. However, this reliance on the litter layer likely reflects selection of habitats with abundant arthropods for food. To investigate this possibility, we examined relationships between Swainson's Warbler presence and both abundance and diversity of ground-dwelling and litter arthropods. In 2004 and 2005, using song playbacks, we surveyed 1453 sites and collected arthropods in litter samples and pitfall traps at 45 randomly selected occupied and unoccupied sites. In litter samples, total mean arthropod abundance, abundance of arthropods ≥5 mm in length, total abundance of adults, and taxonomic richness were significantly greater at sites occupied by Swainson's Warblers than at unoccupied sites. In pitfall data, however, we detected no differences between occupied and unoccupied sites. Additionally, the abundance of several taxa known to be Swainson's Warbler food, most notably beetles, was greater at occupied than at unoccupied sites. Overall, the taxonomic richness and abundance of large arthropods were the best predictors of Swainson's Warbler presence. These results suggest that arthropod abundance and taxonomic richness are key habitat components for Swainson's Warbler. Because the arthropod community may be a driving factor influencing the presence of Swainson's Warbler, management that maintains or improves the leaf-litter layer and promotes ground- and litter-dwelling arthropods will be beneficial for managing habitats for this and other ground-foraging species. © The Cooper Ornithological Society 2011.