The line between bird species, especially those that live in the same area and interbreed, is often fuzzy. Interbreeding of two sparrow species, the Saltmarsh Sparrow and Nelson's Sparrow, has been observed in local marshes throughout Maine, New Hampshire, and Massachusetts. The two have created a "hybrid zone" of mixed-species offspring. This makes it more difficult for scientists to identify species, because they can no longer depend on appearance.

According to a news release, researchers from University of New Hampshire, University of Delaware, University of Maine and the U.S. Fish and Wildlife Service collected and analyzed DNA data from backcrossed generations.

In the region, conservation efforts are of high concern for both of these sparrow species. The Saltmarsh Sparrow is even considered vulnerable to extinction globally, the release noted.

"Our findings show that hybridization can lead to complex combinations of plumage traits making hybrid identification difficult by appearance alone. This also means that it is challenging to monitor the abundance/distribution of hybrids within natural populations without collecting genetic data. Both of these birds are high conservation priorities in the Northeast, and hybrid identification and monitoring can aid in management and conservation initiatives for Saltmarsh and Nelson's sparrows," Jennifer Walsh of UNH said in a release.

Birds were collected from various hybrid zones and classified based on their resemblance to a Saltmarsh Sparrow, Nelson's Sparrow, or a hybrid. Researchers then took blood samples for DNA evidence. These results were compared to physical trait data in order to predict how accurately a species could be identified based on its appearance, the release said.

"Sampling for this study was a big undertaking," Walsh explained in the release. "We sampled 34 sites, spanning about 750 km. Traveling to and accessing all the sites was logistically challenging and we had a lot of support from USFWS and other conservation partners. Every marsh is hugely different in terms of bird density and accessibility. You never really know what to expect until you get there. In general, salt marshes are challenging too--there are a lot of holes and mud and ditches, and you are always working around the tides. It is amazing how quickly the marsh changes--very accessible at low tide, but at high tide you can find yourself swimming back."

Their research was recently published in The Auk: Ornithological Advances, and suggests that DNA sampling of hybrid zone birds is necessary for future identification studies. This will also aid in conservation efforts.

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