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  • NWF Staff
  • Jun 01, 1996
New Mystery From the Mightiest Animal

When biologist Rodger Kram setout to measure the strength and oxygen consumption of rhinoceros beetles, they already had a reputation as the strongest creatures on Earth. Anecdotal reports had some species of the beetles, which exist on several continents, carrying 850 times their own weight. They use their strength for such activities as digging brood tunnels and fights among males that are "like two bulldozers colliding," says Kram.

In his Berkeley laboratory at the University of California, Kram glued Velcro® onto the backs of Xyloryctes thesalus, a species collected in Arizona. He then attached lead strips with adjustable loads on the ends, and he put his study subjects on a tiny treadmill in a special "respirometer" chamber. This winter, Kram reported that his study subject, which weighs about 2 grams and is a bit larger than an almond, was able to move carrying 100 times its body weight—almost half a pound. Loaded with 30 times their weight, "the beetles could walk steadily and for a long time."

Most surprising, the creatures used only an eighth the amount of oxygen Kram had calculated they would use. Some animals are able to use less oxygen than expected with tricks such as dragging their abdomens when carrying big loads. But no known explanations for the phenomenon apply to the mighty and mysterious rhinoceros beetle.

56 Years Ago

In 1940, actress Shirley Temple posed with a U.S. park ranger to increase public awareness of the National Wildlife Federation's conservation stamp program, which helps raise funds for a variety of wildlife and habitat-conservation programs. This year, NWF has released a special commemorative sheet of 36 historical stamps in honor of the organization's sixtieth anniversary.

Got a Wrench?

Plenty of birds use tools, as do other animals, but New Caledonia crows apparently take tool use to a level of technical sophistication not seen before in birds. Ecologist Gavin R. Hunt of Massey University in New Zealand recently reported that he saw the crows use twigs or barbed leaves to probe for bugs in wood or under leaves 52 times. Not only that, on four occasions he saw the birds actually make their tools, pulling a twig from a tree, stripping its leaves and shaping a point at the hooked end of the stick (where it had been attached to a branch). Also, he observed that the crows are careful with their bug-finders, carrying the tools around with them or leaving them "in a secure position on their perch."

Some examples of cruder avian tool use: The brown-headed nuthatch dislodges bark from trees by prying pieces off with other pieces of bark. A red-tailed hawk carrying a struggling snake in southern Arizona was once seen dive-bombing rocks, narrowly missing them in order to smash its prey to death. The Egyptian vulture drops stones on ostrich eggs. And some crows in the United States use cars as nutcrackers by putting walnuts where the nuts will be run over.

If the New Caledonia crows learn how to make their tools by example, their skill may be "a cultural product of crow society," according to zoologist Cristophe Boesch of the University of Basel in Switzerland.

Hiding the Sound of Hunger

Using sophisticated recording equipment and a special sound-analysis program, ornithologist David Haskell of Cornell University has found that the hungry young of ground-nesting birds, such as these worm-eating warblers, make higher-pitched calls for food than do nestlings in trees. The short wavelengths of high pitches scatter in vegetation, and some predators don't hear them as well as lower pitches. So Haskell concludes that the calls help the birds foil predators, since the begging calls of nestlings can advertise location, and birds on the ground make especially easy prey.

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