No one knows yet just how many bats were killed by the frigid conditions of last month’s disastrous winter storm in Texas. Reports popped up across the state about thousands of the winged mammals found either dead or dying. The hardest-hit species appears to have been Mexican free-tailed bats, migrants better suited for warmer climates, as well as some species of yellow bats. But we may not know the full scope of the death toll for quite some time, if we ever do—partly because of a quirk in bat physiology.

Read more from Tara Haelle with Texas Monthly here.