Reproductive success is a misleading indicator of nest-site preferences in the Red-winged Blackbird

Several methods are used to detect nest-site preferences of birds. One method postulates that individuals will prefer those nest-site features that increase their reproductive success. To determine which features affect reproductive success, and hence should be preferred, the method examines correlations between reproductive success and various nest-site features. When a statistically significant correlation is found, it is concluded that individuals exhibit a preference for that feature. In the absence of a correlation, it is concluded that individuals are indifferent to the feature. Here, I argue that this method may lead to misleading conclusions. If good sites are abundant, all individuals should choose them. Consequently, there will be little variation in the features of the chosen sites. This limited variation, when related to reproductive success, may fail to yield a statistically significant correlation and thus lead to the erroneous conclusion that individuals have no preference. An alternative method of detecting nest-site preferences is to compare features of chosen sites with features of available sites. In this study, I used both methods to investigate nest-site selection in the Red-winged Blackbird (Agelaius phoeniceus). I compared vegetation features of nest sites with those of randomly selected sampling sites and found significant differences. The differences imply that Red-winged Blackbirds prefer vegetation that grows in small patches and is tall and sparse, and the plants have thick stems. I found no relationship between these vegetation features and reproductive success. These results suggest that Red-winged Blackbirds have strong preferences for certain vegatation features, but these preferences cannot be detected from correlations with reproductive success.