A few decades ago, white storks were facing a dire situation, with populations in their summer home in Europe crashing after years of power-line electrocutions, exposure to pesticides, and huge die-offs in their wintering grounds in Africa. But after years of conservation efforts, the storks are back, and in some places they’re not budging an inch.
That’s what a new study in the journal Movement Ecology says. When researchers stuck GPS trackers on the backs of 48 of the birds in Portugal and Spain, they found that some of the Ciconia ciconia have stopped making the long flight to their usual African stomping grounds. Instead, they are sticking around the Iberian Penninsula to forage in landfills. Many of the 14,000 birds in the region even nest and raise their young on the trash mountains. Other birds that nest in more natural habitat may make flights up to 30 miles to gorge in the landfill.
“It’s a fantastic life, quite relaxed. They eat anything from leftover hamburgers, fish, sandwiches to dead animals,” ecologist and team leader Aldina Franco from the University of East Anglia in the U.K. tells The Independent. “A truck load of rubbish arrives and they grab what they can.”
Sticking around eating trash buns might actually the help birds breed more successfully, though confirming that will take further study. Franco explains in a press release:
"We found that the landfill sites enable year-round nest use, which is an entirely new behavior that has developed very recently. This strategy enables the resident birds to select the best nest sites and to start breeding earlier. Having a nest close to a guaranteed food supply also means that the storks are less inclined to leave for the winter. They instead spend their non-breeding season defending their highly desirable nest locations."
Andrew Farnsworth from the Cornell Lab of Ornithology tells Brian Handwerk at National Geographic that the change of habit isn’t unique to the storks. “This sort of pattern of migratory species becoming resident occurs rather frequently, and has occurred many times over the evolutionary history of birds,” he says. “It's clear migratory behaviors are quite plastic, in that the [storks] are adaptable and can change quickly.”
In North America, the Canada goose, various gull species, and turkey vultures have all changed their natural routines due to trash or habitat alterations made by humans.
There are still plenty of questions to answer about the storks. For instance, why do some of them still migrate while others stay behind? And are the storks sticking around for the more abundant winter insects or the invasive American crayfish? “It’s going to be very hard to untangle all these effects and allocate a cause for these changes in the migratory behavior of the storks,” Franco tells Handwerk.
But there may not be much more time to get answers. An EU directive will begin the process of replacing landfills in Portugal with closed sites in 2018. “This will cause a problem for the storks as they will have to find an alternative winter food supply,” says Franco in a press release. “It may well impact on their distribution, breeding location, chick fledging success and migratory decisions.”