Looks like a classic illustration of Allen's rule (animals in colder climate have shorter limbs) and Bergmann's rule (warm-blooded animals in colder climate are larger).
Note, that these well-known rules developed in the 19. century might not exist. So many animals don't conform to these rules or were not studied that the rules might be cherry picking.
But I wouldn't be surprised that the results may be e.g. due to habitat fragmentation (smaller size to survive in small habitat patches, and longer wings to search for patches of suiitable habitat).