During cold snaps and periods of snowfall, bird seeds provided at backyard feeding stations become even more important resources for American Tree Sparrows, one of the 14 common backyard species studied (photo by Paul Konrad).

When Arctic air and blowing snow send winter temperatures plunging, backyard bird feeders can provide safe havens for wintering birds, especially in northern latitudes. A new research study shows that these kinds of observations are no coincidence: Some birds flee the countryside and find refuge in urban and suburban neighborhoods – utilizing bird feeders provided there – to survive extreme winter weather. The study focused on 14 common backyard species, from birds like Northern Cardinals and Tufted Titmice that have historically lived in more temperate areas to cold weather birds such as Red-breasted Nuthatches and American Tree Sparrows.

Using data from more than 3,500 Project FeederWatch sites in the eastern United States, Ecologists Chris Latimer and Benjamin Zuckerberg studied the connections between winter weather patterns and where birds were being reported. Latimer explained that “FeederWatch is great because it provides a huge dataset of information going back decades, and you can get data from the exact same sites across a large geographic area for nearly 5 straight months over winter. So you can really start to compare when birds are in a certain region and when they’re not.”

Latimer, who conducted the research as a PhD student at the University of Wisconsin with his advisor Dr. Zuckerberg, selected 3 winters over the past decade for their study, including the dreadful winter of 2014-15 that included a polar vortex and the second-coldest February ever recorded by NOAA.

The researchers divided the landscape into 3 habitat categories: Forest, agriculture, and urban. They initially hypothesized that birds would be more likely to move out of agricultural areas and cities and into forests during harsh winter weather events, because forests can buffer extreme temperature swings. But the study revealed that species such as Carolina Wrens, House Finches, and Northern Cardinals – 3 of the least cold-tolerant bird species in the study – did the reverse: They moved out of agriculture areas and forests into urban areas during or just after the coldest winter periods.

Downy Woodpeckers, Red-breasted Nuthatches, and Black-capped Chickadees (3 species with greater tolerances to cold temperatures) also showed a pattern of moving into urban areas during cold snaps. Referring to the study results, David Bonter, co-director of the Center for Engagement in Science and Nature at the Cornell Lab of Ornithology explained simply that, “Birds go where the resources are.” Botner, who was not involved in the study, noted that his personal observations at his bird feeders near Ithaca, New York, echo some of the research results. For example, in the study, American Tree Sparrows flocked to human-populated areas in a big way during cold snaps, and according to Bonter’s observations: “No snow, no Tree Sparrows at my feeders. But the second we see snow in inches, 15 to 20 Tree Sparrows show up.”

American Tree Sparrows prefer to eat the seed heads of winter grasses and flowers found in open areas. But when deep snow covers the ground and plants, the sparrows must look for other sources of food. Latimer, who now works for The Nature Conservancy, says bird feeders may be helping birds such as American Tree Sparrows.

He also explained that the urban heat island effect may also be playing a role. Average winter temperatures can be up to 10?F warmer in urban areas than rural areas. According to Latimer, the combination of plentiful food and more moderate winter temperatures in cities may help species that historically had more southern distributions. “As winters become more unpredictable, urban areas may provide a refuge for birds like Carolina Wrens and Northern Cardinals as their ranges are shifting north,” Latimer added.

The original article by Marc Devokaitis can be reviewed in the All About Birds website at https://www.allaboutbirds.org/news/urban-feeders-may-be-havens-for-rural-birds-during-harsh-winter-weather/ and the research article published by Latimer and Zuckerberg can be accessed in the Journal of Animal Ecology at https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2656.13332

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