Models of large-scale breeding-bird distribution as a function of macro-climate in Ontario, Canada

Aim We modelled the relationship of breeding evidence for five species of f orest songbirds (ruby-crowned kinglet (Regulus calendula) Blackburnian warb ler (Dendorica fusca), black-throated blue warbler (Dendroica caerulescens) , bay-breasted warbler (Dendrioca castanea) and Connecticut warbler (Oporor nis agilis)) and a variety of macro-climate variables to examine the import ance of climate as a factor determining distribution of breeding in these s pecies and to assess the usefulness of spatial predictions generated from t hese models. Location modelling was conducted over the entire province of Ontario, Canad a, an area of approximate to 900,000 km(2) Methods Data on the distribution of breeding in the province was derived fr om the Breeding Bird Atlas of Ontario. We used logistic regression to model the relationship between the probability of breeding (assessed in 10 km x 10 km blocks) and estimates of a variety of climate variables at the same s cale. Models were selected that had the least number of explanatory variabl es while at the same time having close to the best possible classification accuracy. Results The final models for these five species had from one to six explana tory variables and an overall concordance of 70.4% to 86.3% indicating a go od classification accuracy. Results from subsampling 50% of the original da ta ten times indicate that (1) the classification accuracy of the model for data used to generate the model is not very sensitive to the specific obse rvations used to generate the model (2) the classification accuracy of lest data is close to the classification accuracy of the model data and (3) the classification accuracy of the test data is not dependent on the specific observations used to generate the model. We generated a spatial prediction of the probability of occurrence of each species for Ontario using the rela tionships defined by the logistic regression models and using 1 km gridded estimates of the necessary climate variables. These probability maps closel y matched the maps of observed evidence of breeding from the Atlas. Main conclusions Although mechanisms controlling breeding distribution cann ot be determined using this method, we can conclude that (1) macro-climate is an important factor directly and/or indirectly determining distribution of breeding in these species and (2) spatial predictions of probability of breeding are accurate enough to be useful in predicting probability of bree ding in unsampled areas.