Edge Effects and Ecological Traps: Effects on Shrubland Birds in Missouri

Abstract

The effect of habitat edge on avian nesting success has been the focus of considerable debate. We studied relationships between habitat edges, locations of nests, and predation. We tested the ecological trap hypothesis for 5 shrubland bird species in the Missouri Ozarks. We compared habitat selection and daily nest predation rates among 3 distance-to-edge categories. Edge effects were species specific. Indigo bunting (Passerina cyanea) and northern cardinal (Cardinalis cardinalis) preferred nest sites that were close (Icteria virens)and prairie warbler (Dendroica discolor) preferred nest sites >20m from the edge. Field sparrow (Spizella pusilla) used habitat in proportion to availability. Daily nest predation varied by as much as 200-300% among distance-to-edge categories but did not decrease monotonically with distance from edge. The nest predation models without distance-to-edge categories were ranked the best models based on Akaike's Information Criterion; however, Akaike weights indicated some support for alternative models with distance-to-edge categories. Edges did not act as ecological traps for shrubland birds in this study because habitat preference was not positively correlated with nest predation across the 3 distance-to-edge categories. Researchers and land managers should not assume that shrubland birds respond to edges in the same way that forest species respond to edges. Furthermore, species with similar nesting ecology do not necessarily have similar nest-site preferences or nest predation rates in relation to distance to habitat edges.