For bird lovers, the conclusion is unequivocal: sparrows are becoming increasingly rare in the city.

In Paris, the League for the Protection of Birds (LPO) monitors this species, among others.

"Most of the colonies that we know are close to what is called 'the threshold of collapse'", warns Philippe Maintigneux, volunteer at the LPO.

"The colonies that thrive, you can count them on the fingers of your hand," he adds, especially in places that allow birds to nest away from predators.

A sentinel species

Thermal renovations?

Pollution ?

Malnutrition?

The causes of the sparrows' collapse are manifold, but the scientific community is still struggling to solve the mystery.

"The disappearance of sparrows in Paris is really enigmatic. We don't know exactly why sparrows are disappearing," explains Frédéric Jiguet, ornithologist at the National Museum of Natural History.

For the researcher, the disappearance of one of the most common birds in France should nevertheless challenge the public: "It is still a signal that there is something in the environment that kills living beings."

Noise pollution and malnutrition: two factors pointed out

In Deux-Sèvres, Frédéric Angelier, researcher at the CNRS, is also looking into the question.

The Center for Biological Studies in Chizé is one of the only places in France equipped with aviaries for raising house sparrows for research.

The researcher was particularly interested in the role of malnutrition and noise pollution, which have been little studied.

But again, the mystery remains.

"We were able to show that road traffic did not

have a very marked effect a priori

", says Frédéric Angelier.

Physiological analyzes have however shown that sparrows in the city have a higher level of stress hormones, directly associated with the fact that juveniles do not have access to suitable food.

Same story as Parisian ornithologists, for Frédéric Angelier, there is not just one cause for their decline, he speaks of a "complex" situation.

"These birds are able to cope with one constraint, two constraints, but when you multiply these constraints and they interact with each other, it goes beyond the birds' ability to adapt," he concludes. 

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