Edition: U.S. / Global


Published: March 18, 2003

Stealing, Ever So Gently

A crow is one tough bird. It fights, eats roadkill and trash bin delights and even vandalizes cars. (Crows have been known to rip the blades off windshield wipers.)

Some crows, in fact, would steal food from their own grandmothers. But according to new research, they would do it in a gentler way than when stealing from a nonrelative. Even crows, it seems, have a soft side.

Researchers at the University of Washington studied Northwestern crows at a park along the Puget Sound north of Seattle. In previous studies, they had shown that this species was always on the lookout for chances to steal food from others in its flock.

In their current study, described in the journal Bird Behavior, the researchers used DNA analysis to see which crows among 55 banded birds were related. Then, over hundreds of hours, they watched banded birds stealing food from one another.

The team found that the birds changed their behavior depending on whom they were stealing from. When a bird coveted a nonrelative's food, the thief took an aggressive approach, often flying at the other bird, chasing it, cackling at it and bumping into it.

When a bird sought to steal from kin, however, a much more passive approach was taken. The thief would sidle up to its relative quietly in an effort to get at the food. This stealth approach seemed to work. Often the other bird, confronted in this way, voluntarily gave up its food.

Shrinking Salmon Eggs

For a salmon egg, life in a hatchery is all Champagne and caviar. There are no predators, and water temperature, oxygen content and food are all optimized for growth.

But could a hatchery prove to be too much of a good thing? A new study suggests that it could, particularly if hatchery fish supplement the stocks of a threatened or endangered species.

The study, led by a scientist at the University of Windsor in Canada and reported in the current issue of Science, focused on how egg size evolved in captive-bred salmon. Normally, in the dog-eat-dog conditions of the wild, the larger the egg, the larger and fitter the fry, and the more likely it is to survive.

But a hatchery plays around with natural selection. Where there is essentially no competition for food, smaller eggs can survive as well as larger ones. A result, the researchers said after studying successive generations of Chinook salmon at a hatchery in British Columbia, is that over time, average egg size becomes smaller.

Smaller eggs may not be a problem if all a hatchery is doing is producing farm-raised fish. But when fry from a hatchery are used to supplement wild populations as part of conservation efforts, the small-egg tendencies of the captive-bred can spread to the wild population through interbreeding. That may hinder efforts to restore a species.

The researchers found, in fact, that some mixed populations did show declining egg size. Studying Chinook in two rivers where captive-bred fish have been used to supplement wild stocks, they found that egg size had declined over two decades. In two rivers where few hatchery fry had been introduced, egg size remained relatively constant.

SETI Reaps 150 Points

The SETI@Home project, in which millions of home computers have analyzed interstellar radio signals for signs of alien civilizations, is investigating 150 of those signals in more detail.

Starting today, project scientists from the University of California at Berkeley are at the Arecibo radio telescope in Puerto Rico. They will aim the scope at 150 points that are sources of the signals that were determined to be interesting enough to warrant further investigation.

The scientists caution, however, that the odds that they will actually confirm the existence of an alien civilization are exceedingly slim.

Drawing (Nurit Karlin)