HABITAT RELATIONS OF SHRUBSTEPPE BIRDS: A 20-YEAR RETROSPECTIVE

Documenting bird-habitat relationships by statistical modeling has been a cornerstone of avian ecology for decades, but rarely is the predictive capacity of such models tested. To evaluate how well quantitative models of habitat relationships developed during an initial survey period predicted species distributions and/or abundances in a later period, in 1997 we revisited 13 shrubsteppe sites that we had previously surveyed from 1977 through 1983. Using multiple regression (linear and logistic) and classification and regression trees (CART), we developed habitat models for each species based on the historic period. R 2 values for these models ranged from 0.45 to > 0.95. We then predicted bird species distributions and abundances by using the 1997 habitat attributes as inputs for the models derived from the earlier data. These models generally failed to predict 1997 bird distributions and abundances accurately; only 1 of 14 multiple regressions and 2 of 14 CARTs explained a statistically significant amount of variation in the target species. Thus, although the models may capture relationships between a species and environmental variables when aggregated over multiple years, they may not adequately predict the subsequent distribution and abundance Of Populations over shorter time scales. This result may limit the usefulness of multivariate habitat models in resource management.