BOXES, BARNS, AND BRIDGES - CONFOUNDING FACTORS OR EXCEPTIONAL OPPORTUNITIES IN ECOLOGICAL-STUDIES

Moller (1989) brought attention to several potential shortcomings of nest box studies of passerine birds, including presumed lower predation rates and lower parasite loads compared to nests in natural cavities. These and other factors are certainly influenced by characteristics of nest cavities. Unfortunately, it is not possible to compare studies of birds breeding in nest boxes with birds breeding under unaltered conditions, since no study is free of human influence. More importantly, these differences are only problematical when one views populations as "finished products" adapted to one set of "natural" conditions (the absence of nest boxes). However, conditions are not constant, and evolution designs individuals that are plastic in their response to altered environments. Thus, there is no a priori reason to expect that the behaviors exhibited under altered conditions should be maladaptive or artefactual. Rather than a problem limiting the generality of a particular type of study, nest boxes offer important opportunities and allow study and manipulation of phenomena otherwise difficult or impossible to address.