When This Water Bird Is Hungry, It Simply Summons Food to the Surface - phalaropes - Brief Article

National Wildlife, Oct-Nov, 1998

Watch a dancer pirouetting on stage, and you have a sense of how phalaropes pass their time on lakes and at sea. Other than people, the small shorebirds are the only spinning vertebrates. They not only gyrate as gracefully as ballet dancers, but while they spin they peck--180 times a minute--at brine fly larvae and other tiny organisms. Top that, Baryshnikov!

"We've had birds [in the lab] go literally for hours, just sitting in place spinning away, not stopping," says Margaret Rubega, an ornithologist at the University of Nevada at Reno. Rubega is among a group of scientists that has investigated the mechanics of phalarope feeding. The researchers have demonstrated with high-speed photography that by spinning on the water's surface, the bird generates a rising current that lifts food from lower in the water to within reach of its long bill.

Buoyant as corks, with dense, air-trapping plumage on their bellies, phalaropes are ill-equipped to dive. Instead, when their prey is not abundant at the surface, they spin like tops and summon dinner using their feet to generate an upwelling. "They've evolved this trick of bringing the food to the surface instead," says Rubega. "You don't have to dive if you can bring the stuff up to you."

All three phalarope species share this unique spinning trait. Wilson's phal- aropes nest on prairie ponds in Canada and the northern United States, and in winter fly to South America. The other two phalaropes--the red-necked and red--range around the globe; they breed on arctic and subarctic tundra after which they spend most of the year at sea.

Rubega and her colleagues studied red-necked phalaropes borrowed from Mono Lake in east-central California. The salt lake on the edge of the Great Basin Desert is a major staging area for the species; birds migrating from Alaska fatten on Mono's brine fly larvae before flying to waters off Peru.

The researchers found that a phal- arope spinning for prey in an aquarium swam in tight circles at a rate of about one revolution per second. To set itself twirling, a bird kicks its outer leg harder than the inner one. As it spins, the phalarope kicks away water at the surface, and deeper water rises to replace it. The upwelling current is strong enough to raise plankton from as deep as a half meter, not bad for a bird that weighs scarcely more than a sparrow.

Phalaropes are also "handed," according to Rubega: "At least in the laboratory, some birds will always spin to the left and some will always spin to the right."

Spinning is impressive enough, but the birds also manage to keep their eyes on upwelling prey the entire time they are gyrating. "It's basically the same thing a ballet dancer does when they're spinning around on one toe," notes the scientist.

In a technique called "spotting," pirouetting dancers keep themselves in place by focusing their eyes on one point. They watch that spot while their bodies spin--until their necks no longer permit their heads to stay facing forward. At that point, the dancers snap their heads around and refocus on the same spot.

Like the dancer, the phalarope spins its body but keeps its eye on its target. "They turn their heads on their necks so that they can keep their eyes on the prey, until they can't do that anymore," explains Rubega, "and then they'll snap their heads 45 degrees to sort of catch up with their bodies and to keep their eyes on the same object."

Detecting, seizing and swallowing as rapidly as 180 times per minute, phal-aropes may feed more quickly than any other species of bird. Not surprisingly, all that twirling and pecking takes a lot of energy, and phalaropes do not spin when food is abundant at the surface.

In courtship, phalarope females take the lead and the males rear the young. Larger and more colorful than the males, female phalaropes mate with one male, lay eggs and move on to mate with another bird. The male phalarope constructs the nest and incubates the eggs, even developing a brood patch of bare skin on his breast to warm them. This mating system occurs in less than one percent of bird species.

Adult females are first to leave the breeding grounds, heading south in summer to staging areas like Mono Lake. Until recently, phalaropes and other birds that visit that saline lake faced an uncertain future. That's because half a century ago, the Los Angeles Department of Water and Power dammed four of the five freshwater streams that feed the lake, and diverted the water to the booming metropolis hundreds of miles to the south. Deprived of that water, the lake shrank by half and grew increasingly salty. Conservationists feared a collapse of the ecosystem that generates vast numbers of brine shrimp and brine flies--the invertebrates that feed a million migrating birds every summer and fall.

Decades of work by grass-roots activists led to a 1994 agreement that Los Angeles will curtail future water diversions from Mono Lake. That settlement means that many phalaropes will continue to have a place to rest and feed on their migration across western North America. But there are new causes for concern about the birds at the eastern end of the continent.