As temperatures rise in northern regions, migrating species are seeing less benefit from heading north for the summer months, according to scientists who reviewed 25 recent studies.
In the warm months, birds, mammals, and insects head north to access food, escape predators, and avoid diseases made worse by summer heat. But with climate change, many species are seeing shrinking food supplies and encountering new parasites and pathogens in the Arctic. This has stunted reproduction and increased mortality among migrating species, the scientists write in the journal Trends in Ecology & Evolution.
“Lemmings and voles used to be the main food source for predators such as foxes in the Arctic, however the milder winters can cause rain to fall on snow and then re-freeze, preventing the lemmings from reaching their food,” said Vojtěch Kubelka, a biologist at the Global Change Research Institute in the Czech Republic and lead author of the study. “With fewer lemmings and voles to feed on, foxes eat the eggs and chicks of migratory birds instead.”
Bats, caribou, saiga antelope, and monarch butterflies number among the hundreds of species that travel more than 1,000 kilometers each year to reach northern breeding grounds. The cost in time and energy has historically been rewarded with more food and greater safety, but that is no longer the case for many species, the study showed. While some may head even further north to compensate, risks loom for many species that are hardwired to migrate, even as it becomes less profitable to do so.
“These findings are alarming. We have lived with the notion that northern breeding grounds represent safe harbors for migratory animals,” Kubelka said. “On the contrary, numerous Arctic and North temperate sites may now represent ecological traps or even worse degraded environments for diverse migratory animals, including shorebirds, caribou or butterflies.”