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Grassland birds are declining in North America

Red-winged Blackbird, © Alan D. Wilson, www.naturespicsonline.com

In North America, many common grassland and shrubland birds are declining, apparently in response to ongoing changes in agricultural land use. One striking example is Red-winged Blackbird Agelaius phoeniceus which is declining in 25 out of 38 states in the USA.


Correlation between population trends of Red-winged Blackbirds and rangeland extent in the USA

Murphy (2003)

In North America, many common grassland and shrubland birds are declining, apparently in response to ongoing changes in agricultural land use. An analysis of state-level Breeding Bird Survey (BBS) data highlighted the plight of 63 species breeding in the open-country habitats of the agricultural landscape of eastern and central USA (Murphy 2003). Birds breeding in grassland habitats are faring particularly badly, with 15 of 25 species (60%) showing significant negative trends over the period 1980–1999, and an average decline of 1.1% per year. Overall, some 78% of grassland and shrubland species showed one or more statistically significant correlation between state-level BBS trends and changes in farmland landscape. Of particular note were declines in the total area of ‘rangeland’ (lightly grazed grassland) of 1.0% per year, which were positively correlated with population declines in 12 species. One striking example is Red-winged Blackbird Agelaius phoeniceus, one of the most familiar and abundant birds in North America (Jaramillo and Burke 1999, McCracken 2003). This species has declined at rates of 1% per year in eastern and central USA (Murphy 2003), with even greater declines observed in Canada (McCracken 2003). Although direct control programmes have probably also played a significant role in its decline (McCracken 2003), changes in the extent of rangeland cover accounted for 30% of inter-state variation in BBS population trends.



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Related Species

References

Jaramillo, A. and Burke, P. (1999) New World blackbirds: the icterids. London: Christopher Helm.
 
McCracken, J. (2003) Bye, bye blackbird? BirdWatch Canada 24: 8–10.
 
Murphy, M. T. (2003) Avian population trends within the evolving agricultural landscape of eastern and western United States. Auk 120: 20–34.

Acknowledgements

Data kindly provided by Michael Murphy (Portland State University, USA).

Compiled 2004

Recommended Citation:
BirdLife International (2004) Grassland birds are declining in North America . Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/63. Checked: 31/07/2014