"Bird Conservation Regions (BCRs) are ecologically distinct regions in North America with similar bird communities, habitats, and resource management issues. They are based on the scale-flexible hierarchical framework of nested ecological units delineated by the Commission for Environmental Cooperation (CEC). These ecoregions encompass areas that are similar in their biotic (e.g., plant and wildlife) and abiotic (e.g., soils, drainage patterns, temperature, and annual precipitation) characteristics. BCRs may be partitioned into smaller ecological units when finer scale conservation planning, implementation, and evaluation are necessary. Conversely, BCRs may be aggregated to facilitate conservation partnerships throughout the annual range of a group of species, recognizing that migratory species may use multiple BCRs throughout their annual life cycle. BCRs also facilitate domestic and international cooperation in bird conservation because these areas of relatively homogenous habitats and bird communities traverse state, provincial, and national borders." - NABCI Tri-national website
BCRs were developed initially from 1998 to 1999 by a mapping team comprising members of Canada, the United States, and Mexico. BCRs were defined through a process of expert consultation whereby CEC polygons from various scales were combined or split to create units corresponding to bird species distribution and requirements, and recognizing practical planning considerations. It was understood that updates to the BCR layer would be made every three years, but this did not begin to occur in an official capacity until 2009.
Starting in 2009, BCR boundaries were formally reviewed by US NABCI and NABCI Canada. As part of that process, several changes were made to US and Canadian BCRs. In parallel, a system of marine BCRs was developed, along with a spatial database. BSC maintains and distributes the authoritative versions of both the terrestrial and marine BCRs and is pleased to make these available for download in various formats below.