Quantifying Bird-HaBitat using a relevé MetHod

The relevé method, a standardized, floristically based vegetation sampling technique developed in Europe, has become a vegetation measurement method used worldwide. Although the relevé method was developed by plant ecologists to classify vegetation, ornithologists have begun to use the method for bird-habitat studies, sometimes including modifications to better sample structural features of a habitat thought to influence bird occupancy. To evaluate the potential for these data to provide information about bird habitat, we compared the use of data acquired using an original relevé method to a modified relevé method to build explanatory bird occupancy models. Furthermore, time and effort required to collect relevé method data were compared against widely used vegetation data collection methods. In 2004-2005, point counts for bird occurrences, relevé vegetation measurements following original methods used by the California Native Plant Society, and a modified relevé method implemented by the California Department of Fish and Game, and time and effort data for both methods were collected in the Sierra Nevada foothill blue oak (Quercus douglasii) woodlands of Yuba and Nevada Counties, California. Occupancy models were built using both the original and modified relevé data for three focal bird species important in California’s oak woodlands. Site occupancy and probability of detection showed strong associations with covariates collected using the original relevé method for spotted towhee (Pipilo maculates), whereas models for white-breasted nuthatch (Sitta carolinensis) were best supported using variables collected from both the original and the modified relevé methods. Environmental variables, which were not exclusive to either the original or modified relevé method, best predicted lark sparrow (Chondestes grammacus) occupancy and were competitive when compared to models built using relevé data for spotted towhee and white-breasted nuthatch. The modified relevé method, on average, was a more efficient method compared to the original relevé method and other common bird habitat quantification methods. Future research should focus on directly comparing data acquired using relevé methods to those of other bird-habitat quantification methods to test the accuracy of data in building explanatory bird-habitat relationship models.