Why are Paris' iconic sparrows disappearing?

For bird lovers in Paris, it's an unsettling observation. Even if they listen closely, the sound of sparrows chirping is almost nonexistent. They used to be France's most common bird species, but colonies have all but vanished in the French capital.  

"Most of the colonies we know of are close to what we call the collapse threshold," says Philippe Maintigneux, a volunteer at the League for the Protection of Birds (LPO). 

The non-profit keeps track of house sparrow populations, among other species, all over the country.

"We can count the number of colonies that have survived on one hand," he adds.

The mystery remains unsolved

Is it the fault of urbanisation? Pollution? Or have the birds fallen prey to an obesity epidemic? Scientists point out a multiplicity of factors driving the decline of house sparrow populations. But their sudden disappearance continues to baffle researchers.

"The disappearance of sparrows in Paris remains a mystery. We don't know exactly why they're disappearing," explains Frédéric Jiguet, an ornithologist at Paris's National Museum of Natural History.

For Jiguet, who has been studying birds for two decades, their collapse should come as a wake-up call to everybody: "It's a sign that something out there in the environment is killing off living beings."

Noise pollution and malnutrition

In the Deux-Sèvres region, Frédéric Angelier, a researcher at France's National Research Institute, is also looking for clues on the silent decline of the iconic species.

Their lab is among a few in the country to breed house sparrows for research purposes. Angelier has been studying the role of malnutrition and noise pollution more specifically, but the science remains inconclusive as to what is killing the birds.

"We were able to show that road traffic did not have a significant impact on the sparrows," he says.

The team of experts were able to prove, however, that sparrows in cities have higher level of stress hormones, which is directly associated with the fact that juveniles do not have access to the right type of food.

Frédéric Angelier agrees with Parisian ornithologists that there is no single cause for the decline of the birds, describing the situation as "complex".

"These birds are capable of coping with one stress factor, two stress factors at a time, but when you multiply them and they interact with each other, it exceeds the birds' capacity to adapt," he concludes.