Why do red and grey squirrels not interbreed?

Being different species means that red squirrels and grey squirrels disagree on more than just territory. They're just not reproductively compatible.

By Luis Villazon

Asked by: Carla Redhead, Weymouth

Red and grey squirrels are different species (Sciurus vulgaris and Sciurus carolinensis, respectively) and are not reproductively compatible. Several million years of independent evolution (grey squirrels are native to North America) have resulted in differences in genetics, diet and habitat that would make interbreeding non-viable, whatever outward characteristics they may share. Hedgehogs and porcupines don’t interbreed either.

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