In Finland, for example, the Northern lapwing and Eurasian curlew have usually built their ground nests on barley fields after farmers have sown their crops in the spring. But as temperatures have risen, the birds are now increasingly laying their eggs before the farmers get to the fields, which means their well-concealed nests are more likely to get destroyed by tractors and other machinery.
Looking at 38 years of data, researchers found that farmers in Finland are now sowing their fields a week earlier in response to warmer temperatures, but the birds are laying their eggs two to three weeks earlier. “This has created a phenological mismatch,” said Andrea Santangeli, a postdoctoral researcher at the Finnish Museum of Natural History and lead author of the study. “The response we’ll see is declines of these birds.”
Caribou show up late for lunch
Caribou in western Greenland follow a strict seasonal diet. In the winter, they eat lichen along the coast. In the spring and summer, they venture inland to give birth to their calves and eat the Arctic plants that grow there.
As Greenland has warmed up and sea ice has declined, however, those inland Arctic plants have been emerging earlier — with some plant species now greening 26 days earlier than they did a decade ago. But the caribou have not shifted their migration as quickly. And scientists have documented a troubling trend in the region: More caribou calves appear to be dying early in years when the spring plant growth preceded the caribou’s calving season.
While that study only found a correlation between warmer temperatures and caribou calf deaths, “it’s consistent with the idea that mismatch is disadvantageous,” said Eric Post, an ecology professor at the University of California, Davis. When Arctic plants green up earlier, they may become tougher and less nutritious by the time the caribou get there and start eating them.
Why don’t the caribou speed up their migration? One possibility is that their reproductive cycles respond most strongly to seasonal signals like the length of the day, whereas plants respond more strongly to local temperatures, which are rising.
In theory, if given enough time, the caribou might eventually adjust as natural selection takes its course and favors individuals that calve earlier. But with the Arctic warming faster than the rest of the globe, Dr. Post said, “the question is whether things are changing too fast for evolution to matter.”