Relationships between nesting populations of wading birds and wetland habitat features

We used data from censuses of wading bird colonies on the Atlantic coast from Maine to Florida {1976-1977) to examine relationships between population sizes of wading birds {herons, egrets, ibises) and 9 key habitat features. Variables included features of the colony site {island size, dimensions, isolation from adjacent land) and surrounding (5 km circle) potential feeding habitat {wetland area). Measurements were made on nautical charts using a planimeter. For 122 colonies on islands, 5 multivariate procedures were used. Because of high correlations among habitat variables, a reduced regression model using only 4 variables performed best. The only variable that approached statistical significance (P = 0.06) was land-water interface distance (i.e., wetland 'edge' within the 5 km circle centered on the colony site).