Tuesday, August 18, 2009

Wilson's Phalaropes

Animal behavior is like a box of puzzle pieces. You examine one small piece and try to figure out how it fits into the big picture.

Female (left) and male Wilson's PhalaropesFor example, most birds are sexually dimorphic. That is, the males and females have different plumages. A male uses his brightly-colored feathers to advertise fitness, attract a mate, and repel other males. A female uses her relatively dull-colored feathers to stay hidden from predators when tending to the nest and young.

Most birds also use a strategy of "monogamy," having only one mate during a breeding season. Many even have multi-year pair bonds, like Bald Eagles, which often mate for life.

But Wilson's Phalaropes (above) aren't like most birds -- they turn those common breeding strategies upside-down. But the puzzle pieces are still there. Can you guess which photograph is the male and which is the female?

Phalaropes are common, but inconspicuous, shorebirds with needle-like bills. Of the three species, Wilson's is the only one that spends much time inland. They nest in freshwater wetlands and, during migration, they stage in great numbers on saline lakes like Mono Lake and Great Salt Lake. Wilson's Phalaropes winter in South America.

During the breeding season, Wilson's Phalaropes show "reversed sexual dimorphism," which is another way of saying that females wear the bright feathers and the males have a duller, more criptic plumage. Why? Because it is the larger females who strut and compete for the males, and it is the males who handle all of the nest tending. Their strategies are reversed, and therefore so are their plumages.

After attracting a mate and laying four eggs in his nest, the female Phalarope will often court additional males and lay more eggs - as many as four clutches in one season. When one female pair-bonds with multiple males, the strategy is called "polyandry," and only about 1% of our bird species do this. (Conversely, about 2% of bird species use a strategy of "polygyny," where one male pair-bonds with multiple females. Red-winged Blackbirds are one example.)

After choosing one impressive female Phalarope to mate with, the smaller, more-cryptic male incubates their eggs and raises their young. Juveniles can walk and swim just one hour after hatching. They can fly after a couple of weeks, and that's when they start venturing off and learning how to be Phalaropes.

When teaching, I like to use a strategy referred to as "laid back." But I'm still surprised by how people respond when they first learn about different mating strategies used by other animals. Often, our first response is to pass judgement on animals based on our human culture. But that's an apples-and-oranges comparison. Instead, we should marvel at how many different paths nature takes to reach the same goal. It's always a fascinating puzzle to try and piece together.

Behind the lens: Photographed from a wobbly kayak with a Nikon D700, 500mm f4 lens with 1.4X teleconverter, in the wetlands along (of all places) Ashley Creek. Wetlands produce much more than just ducks...