Fig. 3. Influence of environmental conditions and breeding phenology on a songbird community vocal activity.

Proportion of variance in the VAI explained by environmental covariates, as determined by linear models. To identify environmental covariates that were significantly predictive (P < 0.1) of the VAI, we used stepwise regression with backward variable selection based on a F test to build linear models for each recording period independently. We also built single-variable linear models with each environmental covariate in isolation. We built the same suite of linear models for the period before and after egg laying dates for the two most abundant songbird species. Points represent mean R² (across sites and years) ± SE. Black circles indicate linear models built with data over the entire 30-day study period. Red triangles and blue squares indicate linear models built considering the period before and after the mean egg laying dates, respectively.