Bird populations are declining, including in the Triangle.
A 2019 study led by bird research and conservancy organizations found “major” population loss among North America’s birds — nearly 3 billion birds have been lost since the 1970s. That’s more than a 25% decline in total bird abundance.
“That finding was a really big shock, and maybe a wake-up call that our ecosystems are no longer able to support biodiversity in the way that they once were,” said Allen Hurlbert, a UNC-Chapel Hill biology professor.
Hurlbert oversees a lab that explores large-scale patterns in biodiversity across the globe. He also runs North Carolina’s Mini Breeding Bird Survey, a bird monitoring program that spans Orange, Durham and Chatham counties.
“It's sort of a picture of winners and losers,” Hurlbert said, about local bird populations. “There are winners and losers to the overall global change that's going on in our area. But, there are more species showing strong declines than species showing increases.”
The survey shows that of about 60 well-monitored bird species in the tri-county area, about 13 species are showing a moderate increasing trend. But 22 species are strongly declining, like the wood thrush and northern bobwhite.
Hurlbert said some of that decline is due to increasing human development or the loss of environments associated with small-scale farms. Other contributing factors are direct and indirect results of climate change.
For example, Hurlbert said that a warming climate means that North Carolina temperatures may become less suitable for some bird species. It also means that trees are sprouting leaves earlier in the spring, which can impact other birds migrating to the state.
“The insects that live on those trees are coming out a little bit earlier than they did in the past,” Hurlbert said. “But, if you're a bird wintering in Central America, and you don't realize that spring has started already, by the time you arrive, and you find a mate and have young to feed, it could be that that peak of insect food has already passed. So you don't have as much food.”
Hurlbert said that the public’s participation in projects like Caterpillars Count! and eBird plays a crucial role in helping researchers monitor bird and insect populations.
“Getting information about what birds are doing, when they're around, when they migrate, and also how much bird food is around and available — those pieces of information are really hard to get at a lot of different places simultaneously,” Hurlbert said. “It's really the general public that allows us to fill in the gaps of our understanding across the map.”
On the topic of insect populations, Hurlbert added that this year, caterpillars may catch a break from their typical fate as a snack for birds. That’s because red-eyed cicadas, known as Brood XIX, are emerging in North Carolina this spring after 13 years underground.
“Many species of birds gorge on these cicadas,” Hurlbert said. “When they do that, it has these indirect effects on ecosystems, because they actually ignore the caterpillars that they otherwise prefer. So, there's more caterpillars present in a cicada year. Therefore, there's more damage to the plants.”
Hurlbert said he hopes to assemble a group of undergraduate students to research the potential damage this summer.
