Broad-scale heterogeneity influences nest selection by Brown-headed Cowbirds

Torre J. Hovick, James R. Miller

Research output: Contribution to journalArticlepeer-review


Increasing habitat heterogeneity is widely considered to improve conditions for biodiversity. Yet benefits for native species depend on scale and the effect of heterogeneity on key processes influencing survival and reproduction. We examined the relationship between habitat heterogeneity and brood parasitism at multiple scales in a region characterized by (1) relatively high cowbird abundance, (2) high abundance of our focal species, the grassland obligate Grasshopper Sparrow (Ammodramus savannarum), (3) variation in the structure and composition of grassland habitats, and (4) a gradient of woodland cover in the landscape matrix. Tree cover at broad scales was found to have the greatest impact on parasitism while factors at finer scales were relatively unimportant. We found that for every 1 % increase in tree cover within 1 km of Grasshopper Sparrow nests, the probability of parasitism decreases by 3 %. Parasitism reduced clutch sizes and the number of Grasshopper Sparrows fledged, but survival rates were similar between non-parasitized and parasitized nests. Furthermore, simple population projection models indicated that parasitism has the greatest impact at moderate survival levels and can inhibit the resiliency of this population. Our results support the hypothesis that cowbirds prefer forest hosts, which may reduce parasitism rates on grassland birds in heterogeneous landscapes. Collectively, our findings suggest that the effect of cowbird parasitism may be greater for Grasshopper Sparrows than was previously thought.

Original languageEnglish (US)
Pages (from-to)1493-1503
Number of pages11
JournalLandscape Ecology
Issue number8
StatePublished - Oct 2013


  • Demography
  • Grasshopper Sparrow
  • Grasslands
  • Grazing
  • Nest survival
  • Parasitism
  • Prescribed fire

ASJC Scopus subject areas

  • Geography, Planning and Development
  • Ecology
  • Nature and Landscape Conservation


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