Wildlife

Global Warming Affecting Migratory Birds

The arrival of migratory birds at northern breeding grounds typically coincides with the growth of spring plants. A team of researchers from several universities studied data collected by citizen scientists and satellites between 2001 to 2012 in an attempt to see how climate change is affecting the birds’ ability to accurately time their arrival at these breeding grounds. Their research has been published in Scientific Reports.

Of the 48 North American songbird species that migrate north, the researchers found that nine — almost 20 percent — didn’t reach the grounds by the deadline critical for mating and breeding the next generation of birds. On average, the gap stretched by more than half a day each year across all species, for a total of five days per decade. However, the change for some species was far more drastic — double or triple that pace.

This delay was due to the effect of warmer temperatures on the growth cycles of plants. The birds leave their southern homes at the same time every year, basing their departure on the amount of daylight, which remains unaffected by climate change. However, climate change is altering when plants put out new leaves, with plants in eastern North America “greening up” sooner than normal, while plants in the western part of the continent are undergoing the process later.

This means birds are arriving either too soon and being met with frigid temperatures or too late and missing out on the insect boom that coincides with the new plant growth. Either condition means the birds have a much lower chance of surviving and reproducing, so the nine species identified in the study are therefore in danger of dwindling numbers.5