A new study suggests that Europe's white storks are skipping their annual migration trip to their traditional wintering grounds in Africa, opting instead to feast year-round on "junk food" in the landfills of Spain and Portugal.
This activity indicates that storks have joined an expanding number of migratory species that have changed their biological behaviors due to human influences and global changes in the environment.
It has been known since the mid-1980s that storks are increasingly no longer migrating to Africa for the winter, but a new study is the first to establish that the large birds are now nesting and living close to landfill sites all year round.
"Portugal's stork population has grown 10 fold over the last 20 years. The country is now home to around 14,000 wintering birds, and numbers continue to grow," said study co-author Aldina Franco, a conservation ecologist from the University of East Anglia's School of Environmental Sciences.
"This study looked at the birds' reliance on landfill food, we found that the continuous availability of junk food from landfill has influenced nest use, daily travel distances, and foraging ranges," she explained.
In collaboration with the University of Lisbon and Porto and from the British Trust for Ornithology, Franco's research team followed 48 birds over several years using GPS tracking mechanisms that transmitted the birds' positions five times a day. The trackers also collected accelerometer information, providing detailed information about each bird's behavior.
The findings reveal lifestyles that revolve around garbage. Many storks live permanently in landfill nests, closely guarding these highly sought-after spots. Others live beyond landfills but visit frequently for feasting, sometimes flying distances of 30 miles (48 kilometers) in order to reach the trash, even in non-breeding season.
"These are exciting times to study animal migration. Several species, including the white stork... now have resident populations. We want to understand the causes and the mechanisms behind these changes in migratory behaviour," Franco said.
She noted that there might be benefits to skipping migration, mainly in terms of mating. Birds staying year-round could have a head start because they already have nests ready when the mating season commences.
Why some storks have taken this stay-at-home strategy while others continue to migrate to Africa remains to be researched. "This sort of pattern of migratory species becoming resident occurs rather frequently, and has occurred many times over the evolutionary history of birds," Franco explained, with such species including the turkey vulture and Canada goose in North America.
"It's clear migratory behaviors are quite plastic, in that the [storks] are adaptable and can change quickly," Andrew Farnsworth of the Cornell Lab of Ornithology added. "It's great to have increasingly detailed accounts of how birds are actually exploiting new resources."
At the same time, disrupting their natural avian rhythms could lead to problems in the near future, especially because the European Union intends to shut down open-air landfills by 2018 and the birds will be forced again to readjust.
The study was published in the March 15 issue of the journal Movement Ecology.
