Botteri’s Sparrow Density Changes with Spreading Non-native Habitat in Southeastern Arizona

Abstract

The Botteri’s Sparrow (Aimophila botterii) is a bird of tall grasslands that temporarily disappeared from Arizona following heavy livestock grazing in the 1890s. Its return was noted first in sacaton (Sporobolus wrightii), an uncommon native floodplain tallgrass often >2 m in height, and subsequently in stands of exotic lovegrasses (Eragrostis spp.) spreading into adjacent uplands that otherwise supported shorter native grasslands. From 1999-2001, 18, 10-ha plots (six each of sacaton, exotic, and native upland habitats) were sampled for Botteri’s Sparrow density and vegetative characteristics and demonstrated that exotic grasslands were providing suitable breeding habitat, not functioning as an ecological trap. At that time, territorial density was positively associated with grass height and cover, being greatest in sacaton, intermediate in exotic, and lowest in native upland grasslands (8.5, 5.5, 4.3 territories/plot, respectively). The goal of the proposed work is to measure both the vegetation characteristics and territorial densities on the same plots that were sampled 20 years ago with the expectation that the spread of exotic lovegrasses has continued, now covers a larger proportion of the shorter native grassland plots, and concomitantly supports relatively higher densities of Botteri’s Sparrows on those plots than before.