On the evening trip out of the cave, bat bodies show up as fish-like dots flying by a thermal imaging camera as it faces deep into the cave (the roost is visible as a warm, pale blur) and then pans around toward the cave mouth, visible as a brighter and warmer streak.

Found in "Carlsbad's 8 million 'lost' bats likely never existed" at sciencenews.org/view/generic/id/40178/title/Carlsbads_8_million_lost_bats_likely_never_existed

Video Credit: Nickolay Hristov and Louise Allen