Thanks to Facundo Fernandez-Duque for this excellent student blog
post about Carolina Wrens and their love of feeders in winter. If you
see one visiting you feeder in winter, you might be helping it more than
you think. A Carolina Wren bursts into song. Photo by Laura Frazier from Middleway, WV.
Carolina Wrens (Thryothorus ludovicianus) are small, enthusiastic
insectivores that people hear more often than see. Their diet consists
mostly of insects with only about five percent being seeds and vegetable
matter. Nonetheless, they visit feeders; Carolina Wrens are tiny,
active birds that are constantly in search of food to satisfy their high
metabolic rate. When winters are rough and snowfalls abundant, these
birds may struggle to survive. Thus, their northern range seems to be
limited by harsh winter. However, is that because of the cold, or
because there isn’t enough food in winter? Peanuts are a good choice if you want to attract Carolina Wrens. Photo by Bob Vuxinic from Crossville, TN.
One possibility is that its range is limited by temperature.
Northern, non-migratory birds must face tough winters every year.
Prolonged periods of sub-freezing temperatures, high competition, and
shortages of food all lower the probability of these birds to make it
through winter. However, is it possible that their winter survival rate
can be positively affected by supplemental food?
In 2011, a study done in Michigan sought out to find the answer.
Researches set up an experiment to determine whether supplemental food
played an important role in the winter survival of Carolina Wrens in
their Northern range. They set up sites in three different types of
habitat to test this: city parks, residential areas, and rural areas.
The temperature was also taken into account and recorded hourly. Even
though they found that the city parks had the greatest density and
highest overall temperature, the wrens tended to abandon the site
completely if there were no feeders available. Their study suggests that
Carolina Wrens are directly limited by food supply, and that bird
feeders play a crucial role when other food is in short supply. What type of suet should he choose? This Carolina wren is choosing a peanut based suet. Photo by Aleene Jones from Dunbar, PA.
The snow on the ground can make it hard for these birds to find
food, thus feeders become an important dietary supplement when snowfall
is heavy. Although sunflower seeds might attract more colorful birds,
Carolina Wrens generally prefer suet and peanuts. One peanut alone can
provide more than a third of their daily metabolic need! Furthermore,
Carolina Wrens aren’t the only species that may be shifting its range
according to human influence. The Northern Cardinal (Cardinalis
cardinalis) and Tufted Titmouse (Baeolophus bicolor) have both shown
similar patterns to those of the Carolina Wren. They may also visit our
feeders to help get them through those tough winters!
Reference:
Job, J. and Bednekoff, P. A. (2011), Wrens on the edge: feeders predict
Carolina wren Thryothorus ludovicianus abundance at the northern edge of
their range. Journal of Avian Biology, 42: 16–21. doi:
10.1111/j.1600-048X.2010.05242.x
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