High above the shifting sands of the North American Desert, deathgleaners can be seen hanging in the air, resting on updrafts of wind blown off the sandy ridges below. They circle like vultures, seeking an easy meal on the ground. Now and again, one wheels and banks, signaling to the others that it has found something. Soon, a large group will gather and prepare to feast.
In some instances, it is not food they will spot, but something on the ground that suggests food may not be far away. A deathgleaner's penetrating eye can note shuffling in the sand. It can be a desert rattleback on the move, looking for nourishment of its own. On occasion, deathgleaners will take a young rattleback, but this is not common - the rodent's armor is tough and unpalatable (they also will not risk tearing their fragile wings on an adult's sharp scales). Instead, the bat will follow the movements of a desert rattleback in the hope that it leads to an easier and more abundant source of food.When a rattleback is among the thick, succulent fronds of some desert turnips and is digging down to the tubers, soaring deathgleaners circle in, waiting. A rattleback might unwittingly dig up spinks while searching for desert turnip tubers and this is what the deathgleaners want. Once spinks are on the desert surface, blinded by the light of the sun, down soar the deathgleaners, shadow after shadow swooping in. Long talons, more birdlike than bat-like, pin their prey into the sand. Strong jaws and enormous teeth crush into a smaller vertebrate's backbone, delivering death swiftly. A shattered spink colony will provide plenty of food.
A deathgleaner's wing is typical of the wing of any bat. It consists of a membrane of skin stretched out between the elongated fingers of the hand. This is not the ideal arraignment for a cold-climate animal, since a great deal of body heat is lost through the skin. Birds do not have this problem because their wings are covered in insulating feathers. Deathgleaners avoid excessive heat loss by cooling the blood before it is pumped through the veins of the wing membrane. The heat taken from the blood going into the wings is used to warm the cooled blood coming back from them, by the same principle as industrial heat exchangers.Deathgleaners live in communal roosts, in the caves and ravines of the distant Rocky Mountains. They sleep during the freezing desert night, huddling together to keep warm, and preserving enough energy to travel long distances in search of food. Unlike most bats, deathgleaners are only active in the daytime. They must wait until the sun has warmed the ground sufficiently to make use of warm air currents, or thermals, and soar over great distances. When night comes, temperatures drop to freezing, so deathgleaners cannot fly on such cold conditions, so hunting groups from miles around travel to their communal roosts for the night
When food is particularly scarce, deathgleaners go into a state of torpor, saving energy by slowing down their metabolism. This strategy for conserving energy ensured their survival when so many other mammals and birds faced extinction. As the cold deserts spread over North America, the bats were able to fill the scavenging niche that had been mostly vacated by hawks and vultures.
Once an attack is over and the deathgleaners have eaten their fill, the leftovers are gathered up and carried off. The meat will be taken back to the roost where it will be shared with related members of the colony. This is not a new phenomenon. Vampire bats also shared food, filling special reserves with the blood of prey, which could then be passed on to other individuals of the same kin that had not eaten. By sharing food this way, the deathgleaners aid the survival not only of individuals but of the entire species.