Storks Give Up Migration to Eat ‘Junk Food’

Stork with GPS backpack.
Stork with GPS backpack. / Stork with GPS backpack.

We don’t think too much about our garbage. Once we throw our orange peels and moldy bread in the trash, they vanish. That’s it, as far as we’re concerned. But landfills in Spain and Portugal have taken on second careers as stork buffets, and researchers believe the “junk food” is disrupting the storks' lives. Their report was published in the journal Movement Ecology.

White storks (Ciconia ciconia) are big birds, with wingspans reaching up to 165 centimeters (64 inches). They’re quite common, and their numbers are growing.

“Portugal’s stork population has grown tenfold over the last 20 years,” lead researcher Aldina Franco said in a press statement. “The country is now home to around 14,000 wintering birds, and numbers continue to grow.”

Stork wearing its GPS backpack.

The storks’ range is divided between breeding zones in Europe and Asia and wintering zones in Africa—or at least it used to be. Part of the reason for migration was the absence of available nourishment up north. But with free food just sitting around in landfills, the storks have found no reason to leave.

Storks at the buffet.

In Portugal, the researchers attached GPS transmitters to 48 storks. Five times a day, the devices collected information about the birds’ whereabouts and behavior. With this data, the researchers could tell not only where the storks were flying but what they did when they got there, whether that meant foraging, tending eggs, or standing up to preen. As the researchers expected, the storks were spending a lot of time at the landfill.

Franco says the storks’ switch from part-year to full-time residents has a ripple effect on their lives as a whole.

“We found that the landfill sites enable year-round nest use, which is an entirely new behaviour that has developed very recently," she said. "This strategy enables the resident birds to select the best nest sites and to start breeding earlier."

Once they've got dibs on good nest sites, according to Franco, the storks are also less likely to leave.

“But we also show that as well as those nesting close to the landfill sites, others are willing to travel up to 48.2km to visit landfill sites during the non-breeding season and up to 28.1km during the breeding season," she said. "This is much further than previous estimates.”

For better or for worse, the storks have shaped their lives around the new food supply. But that supply may not be long for this world.

“Under new EU Landfill Directives, rubbish dump sites in Portugal are scheduled to be gradually replaced by new facilities where food waste is handled under cover," Franco explained. “This will cause a problem for the storks as they will have to find an alternative winter food supply. It may well impact on their distribution, breeding location, chick fledging success and migratory decisions."