Visitors may assume all the park's bears are bad-mannered panhandlers and camera hogs, but biologists estimate that only 5 percent of them show up near humans; the rest are shy, and stick to the deep woods.

In the early 1800's, when the explorer William Clark discovered a river crowded with salmon, about 2 million adult salmon a year completed the trip back to their spawning grounds, biologists estimate.

From patterns in the DNA data, biologists can often estimate the sizes of ancient populations and even the approximate dates when one group of people split from another.

Two centuries ago, when the explorer William Clark wrote that the Snake was "crouded with salmon," about 2 million adult salmon a year completed the trip back to their spawning grounds, biologists estimate.

Due to its uniquely suitable environment, biologists estimate that a fifth of all Pacific salmon originates in Kamchatka.

Some biologists have estimated that 17th-century New York Harbor may have contained half of the world's oysters.

Though found from Panama to Argentina, biologists estimate that no more than a few hundred thousand of the animals survive in Venezuela.

By studying the amount of genetic variation in the mitochondrial DNA of the Maoris of New Zealand, biologists have estimated that the founding population must have contained about 70 women.

In 2011, biologists estimate that more than 190 adult coho may have returned to the Russian River watershed, beginning with early storms in October and peaking in December.

Other biologists have estimated that the dead birds represent 15 to 50 percent of the actual total killed - numbers that Exxon has disputed.