March 28, 2014
If you listen and look closely, there's a sign of a changing climate around us. Fuzzy, round little Carolina and black-capped chickadees are shifting northward. Villanova biologist Robert Curry has been studying this phenomenon since 1998. Now the results are in.
"The range of the Carolina chickadee is advancing, and the black-capped chickadee is retreating six-tenths of a mile every year, fairly steadily," Curry says. "It's somewhat surprising. We don't have a good amount of information comparatively across animal populations. That's one of the reasons that this finding is potentially important is that it starts to give us some numbers that we can use to compare against other species."
One of the places Curry and students have seen the change is at Hawk Mountain in southeastern Pennsylvania, the world's first sanctuary for birds of prey.
"The proportion of Carolina chickadees and hybrids at Hawk Mountain, for example, has gone from zero when we started, to almost half the birds now."
Eventually, Curry says, "the black-capped chickadees will probably drop out of Pennsylvania and the Carolina chickadees will take over Pennsylvania. And that will also happen in Ohio and Indiana."
While the chickadees are so abundant that there's no real concern about their extinction as a species, they may run into trouble if they move into areas where their food supply has not shifted to the same degree, Curry says.
Another bit of bad news for the chickadees is that, with all this moving and shifting, there is an area called the hybrid zone where chickadees may mate with a different species. That is, the Carolina chickadees sometimes mate with black-capped counterparts, resulting in hybrids, and poorer reproduction.
Other birds may benefit from Curry's chickadee research.
"It allows us to understand better some of the things that can happen during hybridization that, if we extend some of the conclusions to some of the other species that are affected by both climate change and hybridization, then we may be able to understand the biology of those species that might help us know what to do for management of some of the more critically endangered species.
An example, he says, in our area, is that golden-winged warblers are losing out in range to blue-winged warblers.