Bats, wolves feel the heat

Bats with radiator stripes
Thermal images reveal built-in air conditioning

Plenty of biologists have handled Brazilian free-tailed bats, but none had noticed a feature now revealed by thermal imagery: a heat-radiating stripe on each wing.

In images that show zones of body heat, these bats (Tadarida brasiliensis) look as if they’re wearing pale suspenders as they swoop in and out of a roost in Texas. Once the images revealed where to look, Jonathan Reichard of Boston University looked at live bats and spotted a narrow, ladderlike array of blood vessels running along the wing, near the body.

These stripes appear to be a new example of what biologists call a thermal window, like the blood vessels in a toucan beak, Reichard said. Animals flush these zones with blood to cool down and shunt blood away to avoid chills.

Such flexible thermal regulation could be a boon for vigorous fliers like the Brazilian free-tailed bats, which live in warm places but fly high into cold air to forage. In studying museum specimens, Reichard has found radiator stripes only in the family that includes this species.

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Wolves eat big in warm times
Large elk become prey during drought, study finds

As droughts and a warming trend have gripped Yellowstone National Park, wolves have shifted their dining habits.

Wolves and other large predators were intentionally eliminated from the park in the late 19th and early 20th century. When wolves were reintroduced to Yellowstone starting in 1995, elk calves were a mainstay of their diet during the early part of the winter in the northern range, said Douglas Smith, leader of Yellowstone’s wolf project. As winter wore on and took its toll on elk, adult males became easier prey. Toward the end of winter, researchers found that bulls made up about a third of wolves’ diets.

Data from 2004 to 2008, however, show wolves switching from calves to adults earlier in the winter season. On average, wolves were making fewer kills than in previous years, but each elk provided a larger meal.

Because elk had less vegetation to eat during recent warm, dry years, the males weren’t bulked up to their usual standards when winter came, Smith said. The trials of mating season followed by winter hardship weakened bulls, making them easier pickings for wolves.