ABSTRACTS

Natural History, June, 1999 by Richard Milner

SWALLOWS IN THE STORM Charles Darwin believed that natural selection works gradually and imperceptibly over millions of years, but biologists Charles and Mary Brown, of the University of Tulsa, witnessed selection taking place almost overnight. The Browns study cliff swallows at the Platte River in Nebraska, where they have banded more than 100,000 birds over the last eighteen years. In May 1996, during a six-day spell of cold weather and freezing rain, some 30,000 birds died--53 percent of the total population of 58,000.

The Browns collected more than 1,800 of the dead birds and measured their wings, legs, and beaks. When they captured and measured about 1,000 survivors, the Browns found them to be about 5 percent larger and to have more symmetrical bodies than those that had perished. Subsequent studies of survivors' offspring showed that the traits of larger size and more symmetrical body shape were passed on to the next generation. ("Intense natural selection on body size and wing and tail asymmetry in cliff swallows during severe weather," Evolution 52 [5], 1998)

PLAYFUL OCTOPUSES Play is considered a sign of intelligence and is usually associated with vertebrates. Jennifer A. Mather, of the University of Lethbridge, Alberta, and Roland C. Anderson, of the Seattle Aquarium, wondered how octopuses, which are boneless mollusks, would react to a pill bottle partially filled with water to make it hover in the tanks.

At first, the octopuses brought the bottle to their mouths. Later some blew the bottle away with deliberately aimed jets of water, making the object circle the tank and return to the animals. Some maintained an interest in seizing the bottle and then pushing it away for fifteen minutes or more--behavior characterized by the researchers as an underwater version of playing with a ball. ("Exploration, play, and habituation in Octopus Dofleini," Journal of Comparative Psychology, in press; and, on the Web, "What behavior can we expect of octopuses?" The Cephalopod Page, 1998, is.dal.ca/~ceph/TCP/behavior)

GRIZZLY GARDENERS Grizzly bears serve as inadvertent gardeners when they forage for the bulbs of glacier lilies in subalpine meadows. A recent study in Glacier National Park, Montana, by Sandra E. Tardiff and Jack A. Stanford, of the Flathead Lake Biological Station, University of Montana, has demonstrated that the bears' activities help to spread the plants and en rich the nitrogen content of the soil. Accounts of grizzlies turning the soil go back to pioneer days; in 1824 travelers on horseback were surprised to find what looked like plowed fields in a remote area of Idaho. "On getting to the spot," one wrote, "we observed no less than nine ... grizzly bears at work, rooting away." Measuring internal nitrogen in plants, the University of Montana team found that lily bulbs growing where grizzlies had raked the land had high levels of tissue nitrogen and water-soluble carbohydrates--and produced twice as many seeds as did those in neighboring, undisturbed meadows. "Grizzly bears," they conclude, "must be added to the growing list of species that act as ecosystem engineers." ("Grizzly bear digging: effects on subalpine meadow plants in relation to mineral nitrogen availability," Ecology 79 [7], 1998)

Bumbling in the Dark

When making a beeline for their favorite flowers, bees steer by landmarks, discriminate floral colors, and even note the position of the sun. However, most social bees spend a good part of their lives in the dark--in underground burrows or tree cavities. Lars Chittka, based at the Universitat Wurzburg in Germany, kept colonies of worker bumblebees (Bumbus impatiens) in a dark basement laboratory.

To the researchers' surprise, the bees spontaneously explored their surroundings and foraged for food in complete darkness --on foot. Even more unexpectedly, experimenters showed that bees can sense the distance they've walked in total darkness. Using infrared video, they mapped the bees' walking trails to feeders six feet from the nest. Individuals left odor marks along their paths, but, unlike ants, did not track them closely; the bees never walked exactly the same route twice. When scientists eliminated the odor cues, the bees did not become disoriented. ("Navigation without vision: bumblebee orientation in complete darkness," Proceedings of the Royal Society of London, Biological Sciences 266 [1414], 1999)