Delayed action

Natural History, June, 2002 by Stephan Reebs

Some years, the number of long-legged wading birds nesting in Florida's Everglades--white ibis, snowy egret, tricolored heron, and the like--shoots up to about four times its normal level. Peter C. Frederick, of the University of Florida, and John C. Ogden, of the South Florida Water Management District, noticed such an increase in 1992 after three years of severe drought. Intrigued, the two biologists decided to examine a thirty-eight-year record of weather and nesting data from the Everglades. They found that high concentrations of breeding birds usually appeared one to two years after a drought.

Frederick and Ogden propose two explanations for this pattern. First, dry spells often trigger fires, which release ash and other organic goodies into the otherwise nutrient-poor Everglades environment. When reflooding takes place, these resources are taken up by vegetation and help build abundant fish and invertebrate communities on which the birds can feed. Second, white all fish populations take a hit in theft rapidly shrinking world during a drought, the smaller, omnivorous species may bounce back explosively afterward; the mosquito fish, for example, can breed every three months. Larger fishes that normally prey on smaller ones take longer to rebuild their numbers. For a while, the birds can feast on the bounty of small fish and breed in high numbers. These hypotheses must now be tested--finally, perhaps, a reason to Look forward to the next dry summer. ("Pulsed Breeding of Long-Legged Wading Birds and the Importance of Infrequent Severe Drought Conditions in the Florida Everglades," Wetlands 21:4, 2001)

Stephan Reebs is a professor of biology at the Universite de Moncton in New Brunswick, Canada, and the author of' Fish Behavior in the Aquarium and in the Wild (Cornell University Press).