Background information

North American Breeding Bird Survey

The North American Breeding Bird Survey (BBS) is an international avian survey conducted annually since 1966 in the United States and Canada. The BBS is designed to monitor trends in relative abundance of North American breeding birds at the continental, national and regional level. The BBS focuses on landbirds and is the main source of information on long-term population change for these species in North America.

In Canada, the BBS analysis includes observations from Canadian routes, beginning in 1970 (or a few years later in some areas where there are insufficient data in the early years). BBS results are produced for approximately 300 species of birds, mainly landbirds, with varying levels of precision. There are approximately 600 BBS surveys conducted each year in Canada, the majority of which are concentrated in the southern populated portions of provinces and along the southern edge of the territories where there is a source of skilled observers and road access.

The BBS is analyzed using a Hierarchical Bayesian model that accounts for the effects of variation among observers and routes, first-year observer effects, variations in trend and abundance among strata, and annual variation around a long-term trend. The observed counts are assumed to have an over-dispersed Poisson distribution (Smith et al. 2014). The analysis produces annual estimates of relative abundance, i.e., estimates of the average count of each species on a typical route for each year. Because no estimate of the ability to detect all individuals of a species is available, it is not possible to determine a direct estimate of the true population. Rather, these annual estimates of relative abundance (“annual indices”) are considered an index of the true population. The change in these annual indices over time is then summarized as an annual percentage change, and annual indices are shown in a graph.

The BBS is jointly coordinated by Environment and Climate Change Canada's Canadian Wildlife Service and the Patuxent Wildlife Research Center of the U.S. Geological Survey.

For more information on the BBS in Canada, visit the BBS overview page

For more information on the Canadian BBS results, visit the BBS results page

For more information on the BBS in North America, visit the North American BBS page


Smith A.C., M.-A.R. Hudson, C. Downes, and C.M. Francis. 2014. Estimating breeding bird survey trends and annual indices for Canada: how do the new hierarchical Bayesian estimates differ from previous estimates? Canadian Field-Naturalist 128(2):119-134.