You've heard of the staycation. Some white storks in Europe are now opting for the staygration.
Why? They've developed an addiction to junk food at landfills.
“White storks used to be wholly migratory. Before the 1980s, there were no white storks staying in" Spain and Portugal, says study leader Aldina Franco, a conservation ecologist at the University of East Anglia in the U.K.
“During the 1980s, the first individuals started staying, and now we see those numbers increasing exponentially." (Related: "Beloved Storks, Emblems of Fertility, Rebounding in France.")
For instance, Portugal's resident stork population has grown from just 1,187 birds in 1995 to some 14,000, Franco says. And 80 percent of storks that winter in the region congregate near landfills.
"We think these landfill sites facilitated the storks staying in their breeding sites all year because they now have a fantastic, reliable food source all year round."
For the study, Franco's team caught 48 birds and fitted them with GPS-tracking devices. Over several years, the data revealed the storks were living permanently in landfill nests and guarding those desirable locations, according to the study, published March 16 in the journal Movement Ecology.
The research also revealed avian lifestyles that revolve around trash.
“You see some individuals go from the nest to the landfill site and then just go back to the nest,” Franco notes. (Read more about the myth of storks as baby bringers.)
Storks living farther away would also visit landfills for a feast—some flew distances of 30 miles (48 kilometers).
"It's great to have increasingly detailed accounts of how birds are actually exploiting new resources," says Andrew Farnsworth of the Cornell Lab of Ornithology, who wasn't involved in the new study.
"It's exciting to consider how such changes in behavior may affect the future population of these birds."
For instance, there may be pros and cons of skipping migration, particularly when it comes to mating, study leader Franco says.
Stay-at-home birds may have an advantage because they are on their nests and ready to breed when mating season begins. In future research, Franco plans to find out if that actually equals more success.
She's also curious why some birds have adopted a stay-home strategy while others still migrate to Africa. (See more stork photos.)
Whatever the reason, storks aren't unique in choosing to give up their wandering ways.
“This sort of pattern of migratory species becoming resident occurs rather frequently, and has occurred many times over the evolutionary history of birds,” such as North America's Canada goose and turkey vulture.
"It's clear migratory behaviors are quite plastic, in that the [storks] are adaptable and can change quickly," Farnsworth says.
No More Free Lunch
Another question going forward, he says, is whether such changes in migration are more frequent due to human acitivty. "That's hard to say."
Milder winters due to climate change have also made life easier for storks in Portugal and Spain: Crickets and grasshoppers are more available year-round, Franco notes.
Invasive American crayfish, now common in rice fields, are another favorite new food source. (Watch video: "Stork vs. Mongoose.")
“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," she says.
And for the 14,000 birds living on leftover scraps from the dinner table, the party will be over in a few years.
That's because the European Union plans to close landfill sites with open-air trash piles by 2018, according to Franco. (See "Last Song for Migrating Birds" in National Geographic magazine.)
So what will happen when there's no more free lunch? The birds could starve, but they could also resume their epic journeys in—and out of—Africa.