Why Are London's House Sparrows Disappearing?

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If you guessed that climate-crisis-fueled, disease-carrying mosquitoes are wiping them out, you may be correct.

For many of us city slickers, house sparrows are one of the more endearing urban creatures with whom we share our habitat. In New York City, for instance, despite the charms of our pizza rats and hummingbird-sized flying cockroaches, it's the sparrows that steal the show. The chattering balls of feathers bring a little bit of forest magic to city life.

But in London, the house sparrow has been experiencing a steep decline. According to researchers from ZSL (Zoological Society of London), London's house sparrow (Passer domesticus) population has dropped by a stunning 71 percent since 1995.

Noting that they were once ubiquitous across the capital city, the "sudden, and unexplained decline of the iconic birds" inspired a team from ZSL, the RSPB, the British Trust for Ornithology (BTO) and the University of Liverpool to investigate what was going on.

In their research, they found that 74 percent of the city's house sparrows were carrying avian malaria. That's more than any other bird population in Northern Europe. While it is a strain that only affects birds, it is still cause for alarm – and not just for the birds' sake.

Lead author Dr. Daria Dadam said, "Parasite infections are known to cause wildlife declines elsewhere and our study indicates that this may be happening with the house sparrow in London. We tested for a number of parasites, but only Plasmodium relictum, the parasite that causes avian malaria, was associated with reducing bird numbers."

Just like the malaria parasite that affects humans, P. relictum is spread by mosquitoes that transfer it when they bite to feed. And with a changing climate, researchers expect that avian malaria will become more widespread across Northern Europe, thanks to higher temperatures and wetter weather, both of which abet mosquito reproduction. And the researchers think this could be behind the sudden change with the sparrows, says ZSL.

The authors write, "It has been hypothesized that Plasmodium prevalence will increase across Northern Europe due to climate warming], and that climate change will influence avian malaria infection rates through increased parasite and vector abundance and altered mosquito distributions."

Every day the news seems to offer grim new glimpses of what to expect if we don't turn this ship around and start quelling the climate crisis. City life without sparrows may not seem like the biggest concern, but just like canaries in coal mines, London's dying birds are a potent indicator that things are decidedly not right.

The research was published by Royal Society Open Science.