Monthly Archives: February 2012

Range Contraction of a Once Common Bird due to Climate Change

The Rusty Blackbird (Euphagus carolinus) is a migratory bird in North America. Its usual summer home is boreal forests from Alaska to New England and as far north as the treeline. In winter it migrates to to the southeastern United States. Researchers from Auburn University, Alabama and Archbold Biological Station, Avon Park, Florida examined past and present ranges for populations of the bird across the southern edge of its range comparing data from two periods, 1967-1977 and 1998-2008. Using a generalised linear model with a binomial distribution they tested the probability of extinctions for association with latitude. Time-series analysis and autoregressive moving average modelling, examined correlations between climatic variables and latitude. The result was that Rusty Blackbird populations had become locally extinct and the southern edge of their range had shifted northward by an average of 143km since 1966. Having confirmed that the birds had contracted north, a reason for the shift was put forward.

Studies by other scientists had found that changes in rainfall and temperature had affected moisture levels in bogs and boreal forest lakes in the areas where rusty blackbirds reside and breed. These changes impacted heavily on freshwater macroinvertebrates particularly dragonflies and damselflies, the main food items of rusty blackbirds. Along with shifts from macroinvertebrate dominated systems to zooplankton dominated systems, it is likely that changes in macroinverebrate phenology could be playing a part with temporal shifts in emergence being incompatable with breeding cycles of the rusty blackbirds. The authors acknowledge that while climate change might not be entirely to blame for the range contraction of rusty blackbirds, it is more than likely a major factor. The original article by McClure et al can be found here.

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