Looking, looking, looking…
by Juanita Baker, Ph.D.
“Now where amongst all these reeds are those apple snails!?” Plants provide essential cover for prey to hide from predators. Amongst these reeds where the apple snails flourish, female snails crawl up a stalk to lay hundreds of eggs bunched together, high enough above the water level to be safe from drowning. Snail kite’s diet is almost exclusively apple snails. The snails can’t hide from their sharp eyesight and talons.
From 2003-2009, nest numbers of Snail Kites declined dramatically in Florida, resulting in only about 800 remaining Snail Kites. During that time, invasive apple snails gradually began spreading county to county while native Florida apple snails, Pomacea paludosa decreased dramatically. In 2007, scientists worried that the invasion of the much larger South American apple snail, P. maculata, would be very difficult for juvenile Kites to eat with their small beaks. This might lead to further declines and extinction. However, it was startling to see the Snail Kites beginning to thrive in invaded areas soon after. When the exotic apple snail invaded a wetland or even new reclaimed areas, both Limpkins and Snail Kites became prolific and nesting increased in those areas.
The juvenile survival rate rose from 9% in 2004 to 62% in 2011. Why? University of Florida Dr. Robert J. Fletcher, Jr. and colleagues had been taking measurements of the Snail Kite’s bills, feet, and claws from 2003 through 2012, before and after the exotic apple snail invasion. Christopher Cattau’s comparisons of measurements revealed a startling discovery. The bills, tarsus (ankle/leg), and weight of this predator had increased significantly so they could more easily consume the larger apple snails—they had evolved in 5-6 years in only 1 to 1 and a half generations! This rapid change in gene expression in response to a unique environment is called phenotypic plasticity. The exotic snails offered more abundant and larger packets of food that the bigger billed Kites could better manage, and the Snail Kites thrived.
Cattau, C.E., Fletcher, R. J. Jr, Kimball, R. T. Miller, C. W., and Kitchens, W. M. (2018). Rapid morphological change of a top predator with the invasion of a novel prey. Nature Ecology & Evolution, 2 January, 108, 108–115.