How did the October heat disrupt the biological cycle of animals?

The high temperatures of this month of October, which are just starting to cool off, are not without consequences for wildlife. In France, birds and fish seem completely confused, especially for their period of migration and reproduction. “The storks return to France in January, whereas before, they returned rather at the end of March, reports Cédric Marteau, director of the “protection of nature” pole of the League for the Protection of Birds (LPO).

Temperatures that could disrupt their reproductive cycle

Swallows and swifts have just flew south. The LPO has never observed such a delay in migration. “A week ago, we observed black swifts in Charente-Maritime, while these species normally leave France in July,” says Cédric Marteau. “Most of the storks have gone on migration, but we still see a few that are still in the area,” he adds. “And for the most part, they will not cross Gibraltar, they will stay in the south of Spain because the conditions will be favorable to them and they will come back sooner”, he continues. “We have storks that return to France from January, whereas before, they came back rather at the end of March”, he has noticed for a few years.

These birds then return more fragile because their wintering period in Africa is limited to replenish their resources. This could then disrupt their reproduction.

Bass, mackerel cuttlefish, and spider crabs no longer migrate offshore

Fish also have difficulty migrating… Bass, mackerel, cuttlefish and certain crustaceans such as spider crabs no longer take to the open sea. “Coastal waters cool faster than offshore waters in winter,” explains Eric Feunteun, professor of marine ecology at the Natural History Museum. “So, autumn is the period when many species migrate offshore to seek more temperate waters, and this year, this phenomenon has undoubtedly been stopped”, adds the researcher, also responsible for the marine station of Dinar.

“But food resources in coastal environments are not necessarily there!”, laments Eric Feunteun. “Animals there exert greater pressure on other organisms than usual, it’s the whole ecosystem that takes a hit,” he concludes. Autumn heat could also accelerate hatching, which normally takes place after January. The fish then risk being born deformed, this is what has recently been observed on rays. Hatchlings may also struggle to feed due to lack of food in coastal waters.