The Cassin's Vireo is monitored well by the Breeding Bird Survey (BBS) in Canada. BBS results indicate an approximate 33% increase in the national population since the early 1970s. Annual indices show that the population has fluctuated widely among years, and increased between the mid-1980s and mid-1990s. Overall, however, current abundance falls within the category of "little overall change" relative to abundance levels in 1970 (see Canada graph below). Regionally, results for the interior of British Columbia and Alberta (Northern Rockies Bird Conservation Region [BCR]), where the bulk of the population lives, show an increase, but those from the Northern Pacific Rainforest BCR show a decrease. Elsewhere, regional populations have shown little change. Results for all BCRs which host the species and for which there are reasonably reliable results are shown below. The Cassin's Vireo population is at an acceptable level relative to its national population goal (see Canada graph below).
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
