In Spain, storks’ waste diet is caused by climate change
At the Colmenar Viejo landfill in Madrid, about 100 trucks a day dump household waste into a crater that is then covered with sand by diggers. Hundreds of white storks have built nests up to six feet long on rooftops and in the bell tower of the nearby church. There are even nests on street lamps.
“This is a stork paradise because they have grass, pastures and then the landfill, so they have it all here,” said Alejandro López García, who studies the stork population in Madrid for his doctorate at Complutense University in Madrid.
According to a census, researchers found 36,217 of the approximately 450,000 white storks in Europe in Spain in the fall of 2020. That makes it, together with Poland, the most popular host country for this breed on the continent. In the Madrid area alone, López García said, his working group recently counted 2,300 breeding pairs, compared to just 200 birds recorded in 1984.
The warmer temperatures are likely to continue to rise, meaning more and more birds will be drawn to Madrid in winter. Other species such as swallows no longer migrate further south into Africa. Researchers at the Technical University of Zurich have predicted that the average temperature in the Spanish capital’s coldest month will rise by 3.1 degrees Celsius by 2050.
The storks feed on insects, rodents and worms that they collect from waste to supplement their diet. But for this traditional symbol of luck and fertility, danger lurks among the mounting piles of rubbish.
“With better weather and warmer temperatures, insects and worms are more freely available for the storks to eat,” said Blas Molina, an ornithologist who works with the Spanish bird organization SEO/Birdlife. “But every year, chicks and adults die because they ingest plastic or rubber that they think are worms,” added Molina. “In many cases, their legs get caught in plastic cords that cut off their blood supply, and they eventually die.”
The negative effects of the storks’ waste diet also reach the human population. Storks from all over Europe will still make a short hop south in winter, but feeding on rubbish dumps can transfer potentially toxic chemicals to reservoirs and drinking water sources where they stop along the way. “Any pollutants you have here, or potentially toxic compounds, end up in those waters,” explains López García.
There’s also a clear trend for storks to build nests away from traditional wetlands into adjacent urban areas, López García said. These large birds are extremely loyal to their breeding grounds and will return to them year after year, concentrating their populations around landfills throughout Spain.
Humans and storks are increasingly living side by side, in a sometimes difficult compromise. White storks can boast a wingspan of up to 7 feet and can weigh up to 10 pounds, so need plenty of room to nest. In Rivas-Vaciamadrid, a commuter town southeast of Madrid, the birds have settled in the metro station and local church.
Alderman Carmen Rebollo called the storks “our neighbors” and said the birds were generally loved. However, managing their living space has been a challenge. “The only difficulty we can have with them is that at some point they make nests that are too heavy or can damage a roof, but at that point we try to reduce, modify or move the nests,” she says.
López García admitted that the rapid proliferation of storks around Madrid in recent decades had caused tension. “Areas with two nests in the village church, in the municipality or in the town hall are fine, but if the concentration is 30 nests, then that can start to disturb people,” he said.
Now that the storks have adapted their migratory and reproductive patterns to adapt to the abundant detritus supply, a new threat looms. In 2020, Spain transposed a European Union directive into national law that aims to prevent all organic waste from ending up in landfills. This is precisely the waste that fills with mice, insects and worms that eat the storks en masse.
“This means that the food they eat now will cease to exist,” said López García, who suggested that an area for storks to eat be kept near the dumps. “What we’re proposing is that there’s a smooth transition that doesn’t happen overnight or a closure of landfills.”
However, according to López García, the ultimate benefit of cutting global warming methane by cutting down organic matter in landfills outweighs the benefit of the food source the storks can find here. “In the medium to long term, feeding landfills is negative for them,” he said.
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