Environmental niche parameters of breeding ranges for two subspecies in the Orchard Oriole complex (Icterus spurius spurius and I. s. fuertesi) were characterized via ecological niche modeling. Niche models formulated from museum specimen collections largely agree with published breeding ranges of both taxa. Furthermore, our findings identify likely suitable habitat of migratory double breeding in I. s. spurius. Models successfully identify suitable habitat as illustrated by threshold dependent and independent statistical tests and overlap very little in geographic space. Principal component analysis (PCA) identifies two axes explaining 99.0% of variation in the climate data and reveals that each breeding range exhibits unique ecological characteristics, as they occur in nonoverlapping PCA space. Multivariate analysis of variance (MANOVA) identifies significant differences along both axes (PC1, P < 0.0001; PC2, P < 0.0001). A newly formulated metric for niche similarity (I) agrees with PCA and ENM results and, further, indicates that environmental niche differences are more likely a result of differences in habitat availability than habitat preference. Our results may indicate rapid change in environmental niche within the Orchard Oriole group as these taxa have been diverging for approximately 200,000 y. The Orchard Oriole group provides an example of niche lability that contrasts with evidence of niche conservatism between many other Mexican species pairs.
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