The record was clear, but the mystery remained. Why should wading birds, which depend so much on wetlands, breed with such gusto just as a drought ends? The research, published by Frederick and Ogden in a recent issue of the journal Wetlands, offers a clue.
Getting Rid of the Competition
Wading birds depend on a steady supply of small fish for their diet. But they have to compete with larger fish that also dine on the smaller fish.
During major droughts, there is so little water that nearly all of the bigger fish are wiped out, as well as many of the smaller fish. But most smaller fish, like the mosquito fish, have very rapid reproduction rates. Some can reach maturity and breed within a couple of months. The larger fish take longer, and thus their recovery rate is much slower.
So after a major drought, there are plenty of smaller fish to nourish the birds, and few larger fish to compete with them for that resource. That makes ideal nesting conditions for the birds.
Some scientists think predator fish have little to do with it. Joel Trexler, a biologist with Florida International University, argues that if there's enough water to support the fish after the drought, then the nesting birds will find all they need to survive.
Frederick thinks it's probably both the water level and the absence of predator fish.
But whatever the reason, the research suggests that maybe we ought to think twice about messing with nature. We humans tend to want to "eliminate Biblical disasters," like severe droughts, Frederick says.
"But that may be exactly what the wetlands need," he adds.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.