Bats are worried about glowing city halos, study says

According to a recent study, bats are bothered by glowing halos emanating from cities that interfere with their hunting activities, which is likely contributing to the decline of certain bat populations.

Scientists have shown the impact of light pollution on biodiversity in general, but less well known is the impact of low-intensity halos surrounding urban areas.

Using data collected over seven years by the Vigie-chiro citizen science program in France, the researchers assessed the impact of this diffuse pollution on common serotins.

⋙ Rwanda: Discovery of a bat thought to be extinct 40 years ago.

Light pollution: severe effects on animals

This species, however, is quite resistant to light. “fewer in landscapes polluted by artificial light”summarizes Wednesday in a press release from the National Museum of Natural History (MNHN).

In addition, his nightly activity is later. In a medium-sized city, this activity is delayed by an average of 6 minutes on a clear night and 10 minutes in the case of cloud cover, which enhances the halo by reflecting light coming from the ground, according to a study published in the journal Environmental pollution.

⋙ Animals are increasingly nocturnal to protect themselves from human activities.

A few minutes may seem insignificant, but some bats like serotin. “not to be constantly active at night”, they hunt during a very strong peak just after sunset, lead author Lea Mariton of MNHN told AFP. A peak that should correspond to the presence of the insects they prey on. Otherwise, “even a small shift can have serious consequences”the researcher adds.

Several hypotheses may explain the delay in the onset of serotin activity: a later exit from the roost, the onset of night is less noticeable, or a longer journey to the hunting ground.

“A road with lampposts along it can be an impassable barrier for a bat to find another way.”Emphasizes Ms. Mariton.

A longer flight that requires more energy, so more insects that may not be there when it arrives.

Long-term threat to bats

The study shows the same shift on moonlit nights. But in this case, bats can “compensate” on other nights, according to the study. In contrast, artificial halos are permanent and pose a long-term threat to the health of bats.

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Thus, this study raises the question of the role of light pollution in the 30% decline in the population of serotine vulgaris in France between 2006 and 2019 and the possible impact on species that are more sensitive to light. But light is just one of the threats to these demonized mammals, from habitat destruction to climate change and wind turbines.

⋙ The golden toad is the first species officially extinct due to climate change.

In order to limit the influence of light halos, the study suggests, among other things, to reduce the intensity of the light, change the spectrum of light or the illumination directed to the ground.

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