Choices and consequences of habitat occupancy and nest site selection in sage sparrows

If habitat selection is adaptive, habitat choice by individuals should be d irectly associated with reproductive success. With that expectation in mind , we examined consequences of habitat choice in Sage Sparrows (Amphispiza b elli) in southern California. Habitat selection in Sage Sparrows was pronou nced, with vegetation measurements within territories differing significant ly from those of interspersed unoccupied areas. Likewise, sites where sparr ows placed their nests were significantly different from random sites withi n territories. Both successful territories (those containing a nest that fl edged at least one young) and successful nest sites differed significantly in habitat from those that were unsuccessful. However, there was an inverse relationship between choice and its consequences: the mean score of unsucc essful territories on a discriminant function describing the habitat gradie nt from unoccupied to occupied areas (i.e., choice) was significantly highe r than the mean for successful ones. In other words, birds preferred to set tle in areas in which they did worse. Thus, attractiveness of habitat has b ecome inversely related to its suitability, and the study site now serves a s an "ecological trap." Because predation accounted fur 80-90% of nest loss , we speculate that decoupling of habitat attractiveness from suitability h as been produced by redistribution of predators (mainly snakes) due to anth ropogenic landscape-level changes in the region.