Science Friday: Breeding Bird Surveys

By: Reg Rothwell

Breeding Bird Surveys (BBS) are the source of some of the most important, comprehensive, long-term data on avian populations in North America.  

Initiated in 1966, there are more than 4500 established routes in the US and Canada.  Approximately 70% of these routes are routinely run each year. In Wyoming there are 80 assigned BBS routes and another 28 available, for a total of 108.  In 2015, 72 of the assigned Wyoming routes where run..

BBS routes are run in June of each year during the height of the breeding season.  Of course, the huge variety of birds in a given area have different territorial establishment and breeding time windows, so the timing of BBS tries to correspond with a broad ideal ‘average’ date.  A BBS route is started 1/2 hour before sunrise and lasts approximately 5 hours. The observer stops at 0.5 mile intervals and for 3 minutes counts all birds heard and those seen within 0.25 of a mile.  

BBS data provide an index of trend and relative abundance rather than a complete count of breeding bird populations (a virtual impossibility for all but the smallest, most visible wildlife populations).  The data from individual routes are combined to estimate and monitor population trends and relative abundance of individual species at continental, state, and physiographic region scales. Also, combining species with similar life history traits (guilds) provides insight into the population trends of species with similar needs or ‘occupations’.  This information provides a sense of what is going on with bird populations over time. Sadly, the long term overall general trend, even for what are considered common species, is downward.

BBS data  are used for various purposes beyond determining trend and relative abundance of species.  The data are used to focus research and management actions. They are used to assess bird conservation priorities and to determine the status of Species of Greatest Conservation Need in State Wildlife Action Plans.  Other uses include supplementing state Natural Heritage programs and Breeding Bird Atlas projects, environmental education, and in analyses that advance avian science.