Birds depend on cues from nature to lead their lives — the length of sunlight, temperature changes, ambient scents. For thousands of years, these cues have been remarkably stable and birds have been remarkably consistent in their migration patterns. But in this era of climate change, those cues are getting scattered and birds are getting confused — with potentially dangerous consequences.

A new study in the journal Scientific Reports from US and Canadian researchers examines the migration patterns of dozens of songbird species in North and South America between 2001 and 2012. The researchers used satellite images to determine when birds arrived in their spring habitats.

Historically, birds arrive at the first signs of spring — when plants begin to sprout their leaves, a process known as “green-up.” During the period the researchers studied, birds either arrived too early or too late. The gap in arrival time grew an average of half a day per year, and five days per decade.

For birds migrating in the west, spring has been coming late. For birds in the east, spring has been coming early. This year in particular featured an especially disrupted seasonal change — the “first leaf” of spring arrived nearly three weeks earlier than expected in some places, according to a study by World Weather Attribution.

Read more: Bird Migration Patterns Are Getting Wrecked by Climate Change