Data from the North American Breeding Bird Survey were used to estimate continental and regional changes in bird populations for the 2-year periods of 1993-1994 and 1994-1995. These 2-year changes were placed in the context of population trends estimated over the 1966-1995 interval. The 2-year changes were more positive during the 1993-1994 period, when 54.2% of all species exhibited positive continental trend estimates. This percentage was reduced to 47.7% during 1994-1995, as compared with 50.5% of all species having positive continental trend estimates over then entire survey period. In general, the percentage of increasing species in the Central and Western BBS regions was highest during 1993-1994, with a very marked decline in the Western BBS Region during 1994-1995. The percentage was highest in the Eastern BBS Region during 1994-1995. The continental and regional percentages of species with positive trend estimates were also analyzed for 12 groups of North American birds having shared life-history traits. Over the entire survey period, grassland birds remain the species group with the smallest percentage of increasing species. Trends during these 2-year intervals do not indicate any consistent improvement in the overall declines experienced by grassland birds since the mid-1960s.
Additional publication details
The 1994 and 1995 summary of the North American Breeding Bird Survey