"The idea that there might be arboreal voles is not that radical – after all, tree-climbing and tree-dwelling are all over the place within muroid rodents – but what’s especially odd about Arborimus is that it’s only the females that live in trees; males (while capable of climbing) live in subterranean burrows or in piles of vegetation. In order to meet up with females (who might be 30 m up in the trees), the males do of course climb, and they also build nests in trees during the mating season (this lasts from February to September). Nevertheless, it seems that we have a fundamental difference here in how males and females partition the habitat. Is this reflected in their morphology? I don’t know, and I don’t know if anyone else knows..."

-Darren Naish waxing astonished re. obscure, freaky voles (The tree voles under discussion live in Oregon and California, which I didn't know before today.)