For the Birds Radio Program: Wilson's Phalarope
What pretty, dainty bird gravitates to sewage ponds?
(Recording of a Wilson’s Phalarope)
Sewage ponds may not seem like a pleasant breakfast topic, but they very often attract a variety of lovely birds, which may look out of place but at least have the avian advantage of being unable to smell. A couple of weeks ago, when I was birding at my favorite sewage ponds of all–in Port Wing, Wisconsin, I came upon a pair of my favorite shorebirds of all–Wilson’s Phalaropes.
These exquisite sandpipers are the most specialized swimmers of the shorebirds. The name “phalarope” comes from the Greek word “phalaris” for coot and “pous” for foot–“coot-footed” refers to their toes, which have both fat lobes and partial webbing. These adaptations enable phalaropes to paddle more effectively than other sandpipers. In addition, their lower legs are laterally flattened, reducing drag underwater, and the plumage covering their underparts is dense and duck-like, providing a layer of trapped air which they float on as lightly as corks. This benefit has one small disadvantage—phalaropes are so buoyant that strong gales pluck them up literally out of the water.
There are three species of phalaropes in the world. Wilson’s Phalarope breeds only in the prairie ponds of North America, but the other two species, the Red-necked Phalarope and the Red Phalarope, nest in northern ponds of Europe and Asia as well as Canada and Alaska. All three species have salt glands on their bills like albatrosses and other truly oceanic birds–this enables them to spend at least part of the year in saltwater–the salt glands allow them to drink ocean water and release the excess salt from their bodies.
Phalaropes are as light and buoyant in the air as they are in the water–so much so that they’re tossed around all over the world by strong weather systems. In Newfoundland they’re known as the Gale Birds.
The other unique thing about phalaropes is that they show reverse sexual dimorphism. That is, the females are larger and more boldly colored than the males, and the males do all the incubating and caring for the young. Female Wilson’s phalaropes weigh more than 35% more than males: the average weight of males is about 1 1/2 ounces, and females can tip the scale at three ounces. Females are aggressive in courting males and defending their territory during the brief nesting period. Males drop the feathers in two patches on their abdomen so their hot skin is in direct contact with the eggs–Female phalaropes never develop this brood patch. In laboratory tests, ornithologists have learned that there is as much testosterone produced in the ovary of a female phalarope as is produced in the male’s testis, and sometimes the female produces even more of masculine hormone. In 1977, some ornithologists postulated that these reversed sex- roles are due to the fact that phalaropes nest in ecosystems that have relatively little food. If the female bore the burden of both producing and caring for the young, she would not survive on such a sparse diet, so the male and female both expend a similar amount of energy.
Phalaropes stir up their food by spinning in the water like toy tops. They use their needle-like bill to pick up mosquito larvae and other insect life as it rises to the top of the water while they spin. They also walk along muddy shores feeding in the mud like other shorebirds, but overall, these coot-footed, sex-reversed shorebirds with their duck feathers and albatross salt glands are one of the most interesting birds in the entire avian world.
(Recording of a Wilson’s Phalarope)
This is Laura Erickson, and this program has been “For the Birds.”