Investigating area-sensitivity in shrubland birds: Responses to patch size in a forested landscape

Population declines of shrubland birds in the eastern United States have been attributed to loss of early-successional habitat. Given that shrubland habitats are often ephemeral and patchily distributed, understanding the sensitivity of shrubland birds to patch characteristics is important for conservation. We tested the extent to which patch area was related to shrubland bird density, annual survival, and productivity by examining capture rates, apparent annual survival estimates, and juvenile-to-adult-female ratios for six focal species of shrubland birds in southeastern Ohio. Identical 3 × 3 mist-net grid arrays were set at each of 13 clearcut patches ranging in size from 4 to 16 ha and visited once per week between June and August of 2002–2006. Over the five seasons, 1428 juveniles and 2001 adults of six species were banded. Capture rates for all six species increased with patch area (mean of 44% higher in largest than smallest patch) but this relationship was only significant for the Yellow-breasted Chat (Icteria virens; F1,11 = 34.2, P < 0.001) and the Common Yellowthroat (Geothlypis trichas; F1,11 = 7.0, P = 0.023). However, after accounting for the effect of bird movements on capture rates, capture rates for only four of the six species increased patch area (mean of 22% higher in largest than smallest patch) and this relationship was only significant for the Yellow-breasted Chat (F1,11 = 8.9, P = 0.012). Patch area was not a good predictor of apparent annual survival or juvenile-to-adult-female ratios for any species. Overall, we detected limited evidence of area-sensitivity in our system and no evidence that annual survival or productivity differed by patch area.