Tracking eastern bluebirds is easy when they've dined on artificially fluorescent fruit.
Researchers in South Carolina discovered this recently, when they tried a new method for tracking birds on the wing. All the scientists had to do, they say, was to follow the glowing droppings to discover how the birds use "corridors" to travel between habitats.
"By carefully measuring each flight they took—typically less than 65 feet (20 meters)—and putting those separate flights together in a computer simulation, we could project where a bird who ate a certain fruit would end up in 45 minutes when [the fruit] passed through its digestive system," said Douglas Levey, a zoologist at the University of Florida in Gainesville.
Biologists, of course, are not shy about getting their hands dirty. Animal droppings yield a wealth of natural information. And scientists have artificially enhanced excrement in a vareity of ways to make it easier to trace.
Scientists sometimes track larger animals, for example, by putting magnets in the animals' food and using magnetic detectors to find their droppings.
Researchers have also used fluorescent powders to track animal prints and even to make the animals themselves more visible by coating them with the glowing dust.
But at the Savannah River Site National Environmental Research Park, a U.S. Department of Energy facility near Aiken, South Carolina, Levey's team combined these techniques.
They coated the fruits of the wax myrtle (Myrica cerifera) bush with a diluted form of sticky Wiltproof—an agricultural adhesive to which fluorescent powder binds.
"The birds can't see it," Levey explained. "We can't see it—but under ultraviolet light it will glow."
The team sprayed tens to hundreds of thousands of fruits. Eastern bluebirds (Sialia sialis) in the area soon ate most of them.
The birds then obligingly dropped their feces into well-placed plastic flowerpots near popular perches throughout a large, wooded test area. In the pots, fluorescent undigested pulp and seeds were visible under a flourescent scope.
The team describes its study in the current issue of the journal Science.
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