Humans have long known how useful it is to have a rich friend. They'll pick up the dinner tab, maybe take you on vacation — even give you a handout when times are lean.
A new PLOS ONE paper shows that the same just may go for the animal world, but with slightly different currency and perks. A group of Florida researchers have shown that alligators might benefit from living under the trees of out-of-reach nesting birds in order to come into a payday of dead or otherwise unfortunate chicks. Not exactly courtside Knicks tickets, but the heart wants what it wants.
It's probably no surprise that wading birds benefit from creating a nesting habitat in trees near alligators, as a way to guard against mammalian critters like raccoons and opossums preying on their young. (Think of it like keeping a rabid dog in your front yard, while you remain inside; hopefully, it attacks any trespassers but is prevented from happily chomping on you.) A great deal for the birds, but what's in it for the gator?
The paper found that the alligator isn't just resigned to the arrangement, but may be becoming fat and happy because of it. Egrets, herons, ibises, storks and spoonbills have been shown to lay more chicks than they can raise, a mechanism used by birds in an attempt to create a robust reproductive system. That means that in a battle for food, one or more of the chicks might be pushed out of the nest in an extreme case of sibling rivalry. Those chicks, in turn, become an easy dinner for the alligators that lumber under the nesting sites.
The dietary payday is real. One or two chicks from each nest may not seem huge, but "multiply this times 1,000 nests in a colony, and then multiply that times about 350 grams per chick – that's a lot of food," emails Peter Frederick, a professor of wildlife ecology and conservation at the University of Florida and one of the study's authors.
Of the 39 gators sampled, the mean body condition (a kind of mass index) of the alligators captured near bird colonies was 13 percent higher than those captured away from the colonies. Because alligators need to turn body mass into eggs during their breeding season, the researchers believe that "the 'colony' alligators have a huge advantage here over the non-colony alligators," says Frederick.
The researchers also speculate that birds might have one more advantage for hungry gators — in the form of guano. "The excreta produced by a colony is pretty impressive," says Frederick. "That fertilizes the colony area, and is probably carried by water flow out of the colony. This fertilization may lead to larger populations of fish and other things alligators like to eat."
Alligators, in other words, are not just stooges that are tricked into protecting the nests of their neighbors. Instead, their use as the guard dogs of the wetlands is repaid in highly nutritious dividends.