Earth Almanac: September/October 2009

Gigantic Happy Faces

If the sea wind is down, you’ll often hear them first—long sighs that seem to express profound relief. Then black, glistening bulbous heads and high backs roll into view. Get close enough, and you’ll see their mouths, turned upward in perpetual smiles. They’re pilot whales, the dolphin family’s second-largest member after killer whales (which may prey on them and of which they’re deathly afraid). Males may measure 20 feet and weigh three tons. You can see pilot whales at any time of year—the long-finned species in temperate seas, the short-finned species in the tropics. But now long-finned females will be nursing young. They bear one calf every three years and stay with it until it reaches sexual maturity, which for males is about 12 years. Some females will live for 30 years after they can no longer become pregnant, extremely unusual among animals, and they can live up to 60 years (males can live up to 40). In even more unusual behavior, during these post-reproductive years they may nurse the calves of other mothers. All this contributes to pilot whales’ tight social structure, one that gave rise to their name when it was mistakenly believed that one whale “pilots” the others. But such social behavior has its downside, probably contributing to the mass strandings pilot whales so frequently suffer when they follow their pod mates into shallow water.

Feathered Clouds

The day is windless and cloudless with a sky the shade of azure you see only in September. So why is there a shifting, swirling black smudge above that distant barrier island? Line it up in your spotting scope, and you’ll discover it’s several hundred thousand tree swallows, staging for migration to their winter habitat in the southern states. Other swallows have to push on to Central and South America because they depend entirely on insects. During the cold months, however, tree swallows can subsist largely on fruit—especially bayberries. In addition to their flocking behavior, these highly social birds engage in an apparent game in which they drop a feather from considerable altitudes, then compete to see who can snatch it. The winner climbs, and drops the feather again. And offspring from the previous year will assist parents in feeding hatchlings. Tree swallows are doing better these days thanks to the great popularity of bluebird boxes; European starlings—one of the swallows’ major nesting competitors—cannot fit into them.

Eating Fire