GAINESVILLE, Fla. – The majestic Peregrine Falcon, one of the fastest birds on the planet, can fly hundreds of miles, but lately has been sticking close to home to breed. Researchers at the University of Florida, Institute of Food and Agricultural Sciences say it’s a matter of population density.
Peregrines had almost become extinct from the 1950s to the 1970s, when governments and farmers sprayed vast areas of land with the pesticide DDT, widely used to kill malaria-carrying mosquitoes and other pests, said Madan Oli, a professor of population ecology in the UF/IFAS department of wildlife ecology and conservation. Scientists soon realized that the pesticide was also killing good insects, birds and mammals, he said.
“This led to a ban of DDT, but the damage had been done. Populations of songbirds and larger, fish- and meat-eating birds like the Peregrine Falcon were decimated. The peregrine was listed as an endangered species,” Oli said. “But by the year 2000, the British Peregrine population had rebounded and become stable. Now, you can find them everywhere except Antarctica.”
Oli, his Ph.D. student Elise Morton and a team of researchers in the United Kingdom wanted to know how that population increase would affect the birds’ behavior. Specifically, they were interested to see how far peregrines traveled away from the area where they were born to breed, and if this distance changed depending on population density, and the time period and area over which this pattern was studied.
UF/IFAS scientists examined data collected across the British Isles from 1964 to 2016. “It was important to cover a broad period of time so that we could capture behavior when the population size was both low and high,” Morton said. Their study, published in the journal Ecology, showed that in contrast to expectations, as population density increased, peregrines stayed closer to home to breed.
According to Oli, researchers had long predicted that peregrines would have to travel farther to establish new homes as population density increased, even though traveling away from their place of birth means a lower chance of survival. But that was not the case, he said.
“What we found was really a matter of scale. If we had only looked locally, we would have inadvertently excluded peregrines that migrated longer distances. But, once we expanded our study area to the entire British Isles, we found that they did not disperse longer distances to settle and breed,” Morton said. “It was almost as if the birds figured out that there are high populations everywhere, so they might as well stay close to where they were born and increase their chance of survival.”
The study will help conservationists plan better, Oli said.
“Conservation planners, environmentalists and land managers need to take note that just because the peregrine population in some areas has rebounded, doesn’t mean the birds will follow the traditional route of leaving home to find new territory, food and mates,” Oli said. “And, we have to plan for having more of them staying close to their birthplace.”
Click here to read the study, “Dispersal: A Matter of Scale,” in Ecology.
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