Climate change disrupts migration
In his May 16 article in The Washington Post, Ben Guarino writes of a “looming threat” to songbirds from a changing climate, in which spring begins increasingly earlier each year. Some songbirds can’t keep pace with the shifting start of spring. He quotes ecologist Stephen J. Mayor who, in his new study, concludes that an earlier spring, for some songbirds, can be devastating.
Here’s how it works. Birds know to migrate by changes in daylight. They tend to head north from Central or South America about the same time each year — but here’s the problem. Mayor’s study combines organized bird counts and satellite imagery that tracks the start of green-up, the sudden burst of photosynthetic activity that begins in early spring in North America. His study shows that this green-up is happening a bit earlier each year.
The green-up brings out droves of hungry caterpillars and other insects. But, this insect explosion only lasts for a short time, sometimes fading by the time some birds arrive. The Post explains that “In oak forests, for instance, insects find the young leaves quite tasty. But as the foliage ages, the oak trees deposit bitter tannin compounds in their leaves, making the plant matter difficult to digest or downright inedible.”
Fewer insects equals less food for birds. “If a bird’s timing is off, they may arrive to find their habitats impoverished of food,” Guarino writes.
Timing is everything and the delicate balance that has birds arrive at the perfect time to find just the right food is increasingly out of sync. Climate change is making the arrival of spring more and more unpredictable.
Most birds haven’t been impacted yet, but a few like rose-breasted grosbeaks, scarlet tanagers and indigo buntings are showing a greater mismatch in timing — in other words, arriving at their destinations a bit late.
It’s more than birds that could be affected. Mayor points out in his study that “If birds aren’t arriving when insects emerge in the spring, we could see things like insect outbreaks or defoliation. There are many potential impacts that we don’t have a good handle on yet.”
Let’s be grateful for what has been a wonderful spring migration in the Santa Fe area. Western tanagers continue to appear at local feeding stations, eating lots of suet cylinders and oranges. Black-headed grosbeaks have been plentiful, and we’ve even had a few reports of rosebreasted grosbeaks and blue grosbeaks too.
Lesser goldfinches have been everywhere and easy to attract with thistle feeders. Bullock’s and Scott’s orioles are still moving through. Some are settling in for the summer. Meanwhile, hummingbird activity remains very strong.
Anne Schmauss is the co-owner of Wild Birds Unlimited in Santa Fe and she loves to hear your bird stories. She is the author of For the Birds: A Month by Month Guide to Attracting Birds to Your Backyard and Birdhouses of the World.