Castoridae

I measured bird abundance and richness along the upper San Pedro River in 2005 and 2006 to investigate how beavers (Castor canadensis) may act as ecosystem engineers after reintroduction to a southwestern U.S. desert riparian area. In areas where beavers colonized, I found higher bird abundance and richness of bird groups such as all breeding birds, insectivorous birds, and riparian specialists, and higher relative abundance of many individual species—including several avian species of conservation concern.

The status of beaver (Castor canadensis) in northeastern Sonora, Mexico, is uncertain. We surveyed the Cajon Bonito River to assess the beaver’s status and habitat and found five colonies. Limiting factors appear to be pollution due to animal waste, deforestation of riparian trees, and human exploitation. Beavers did not appear to require habitat diversity as much as dense riparian and aquatic vegetation in waters with low organic content. These kinds of studies are imperative to understanding the natural history and ecology of the species in this unique region.