Table 2.

Climate variables from the MFSL (Rehfeldt et al., 2006) used in Random Forests models for both Current classifications. Number represents variable importance in each model as assessed using the Gini impurity index, which ranks variables based on the decrease of the accuracy of an RF model when a variable is excluded, such that important variables lead to a large decrease in model performance when excluded (Breiman, 2001; Liaw & Wiener, 2002). Dashes mean a variable was not included in the final model

	Current
	Red‐breasted	Red‐naped	Hybrid
Mean temperature of coldest month	1	1	2
First freezing day of autumn	–	–	10
Mean annual precipitation	2	5	1
Growing season precipitation	–	–	4
Frost‐free period (ffp)	6	7	8
Sum of degree‐days >5°C	7	6	5
Degree‐days >5°C	–	–	7
Degree‐days <0°C	4	2	3
Min temperature of coldest month (mmin)	3	3	6
Degree‐days <0°C (based on mmin)	5	4	9