Sparrows are mysteriously disappearing in Berlin. Scientists don't know why

The house sparrow (Passer domesticus) has lived alongside humans for centuries and adapted well to urban life. Once, horses provided a particularly abundant source of food: grain remained in stables and made its way onto the streets with horse manure.

When cars began to massively replace horses in the early 20th century, sparrows lost a rich food source, and their numbers began to decline. For a while, it seemed that the population had stabilized at a lower level.

However, in recent decades, the number of these birds has started to decline again in Western European cities. Possible reasons include modern development, which reduces suitable nesting sites, environmental pollution, an increase in predators, including cats, and a massive reduction in insect populations.

Berlin, however, remained an exception for a long time. It was even called Germany's "sparrow capital." However, over the past five years, the city has lost a significant portion of its sparrows. According to experts, their numbers have decreased by approximately 70% compared to 2021, when there were about 190,000 breeding pairs in the city.

"It's as if they just dissolved into thin air," says the German Nature and Biodiversity Conservation Union (NABU).

The Tagesspiegel publication investigated why sparrows are disappearing.

Why Berlin specifically?

Berlin was considered particularly favorable for these birds because, according to experts, it is "less sterile" than many other German megacities. Green areas here are relatively rarely mown, and there is plenty of food waste on the streets. What might annoy people turns out to be an advantage for sparrows.

However, conditions have not significantly changed in recent years. If the main problem were a lack of food, a similar decline would be observed among other songbirds. But researchers see nothing comparable.

The lack of nesting sites also does not explain the scale of the decline. Many suitable niches in Berlin are simply empty now.

The sharp disappearance of sparrows has led experts to look for a cause among diseases. In particular, they paid attention to avian malaria, caused by single-celled plasmodium parasites. Mosquitoes transmit them.

At higher temperatures, both pathogens and their vectors develop faster and spread better. Therefore, climate change can increase the risk of such infections.

There are grounds for this hypothesis. In 2019, a study of sparrows in London found a link between plasmodium infection and bird mortality. Parasites do not necessarily kill them directly, but they weaken the organism.

For Berlin, no similar study is yet available. Therefore, avian malaria remains only one of the possible causes, and the mystery of the sharp disappearance of sparrows has not yet been solved.

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