Note: This is another story in the Dayton Outdoor Recreation Examiner's series Wild Things:
By Jim McCormac
Ohio Division of Wildlife
For as long as people have been watching birds in North America, the American robin has served as the quintessential harbinger of spring. This distinctive thrush, with its brick red underparts and penchant for stalking suburban lawns, is familiar to nearly everyone.
The arrival of robins at winter’s end heralds warmer days, and the red-breasts usher in an ever-increasing cascade of spring flora and fauna.
John Maynard Wheaton, in an 1879 report on the birds of Ohio, noted that: “…the Robin arrives about the middle of February and remains until November”. While small numbers of robins have probably always overwintered in Ohio, even in Wheaton’s time, most of them fled south. The status of wintertime robins has changed a lot since the olden days, and if you think you’re seeing more of them when the snow flies, you’re right.
Perhaps the best gauge of wintering bird populations is provided by Christmas Bird Counts (CBC). Overseen by the National Audubon Society, CBC’s began in 1900 and have mushroomed from 25 counts to 2,200 worldwide, mobilizing an army of 63,000 birders.
Ohio has its fair share of CBC’s – about 75 at present, in all quarters of the state. As each count covers a 15-mile diameter circle and are undertaken from mid-December through early January, they do a good job of assessing Ohio’s winter bird life.
The last five decades of Christmas Bird Count data illustrates that there are indeed more robins with frosty toes. Ohio counts from 1962 thru 1971 collectively tallied an average of 4,370 American robins each year. That total is peanuts by today’s standards.
The number of wintertime robins has skyrocketed over the last 50 years, and the annual average of Ohio CBC’s over the last decade was a staggering 29,373. The wintering robin explosion is a widespread trend across northern North America. For instance, the province of Ontario, Canada – our neighbor to the north – has documented a similar spike in robins.
The million dollar question: why the major increase in wintering robins? It would be easy to point a finger at climate change, but warming temperatures are probably a minor factor, if a factor at all.
Nonnative plants are the true culprit enticing robins to stay north. In the colder months, robins turn largely to a diet of fruit, and the abundance of ornamental crabapples, hawthorns and other berry-producing landscape plants offers an ever-increasing buffet for the birds.
Even more prolific are various invasive bush honeysuckles, which jumped the garden fence and now run rampant across the land. Honeysuckles produce bumper crops of berries, which robins feast upon.
The availability of a prolific new food supply is not necessarily good for the robin. In general, berries produced by these nonnative plants are the equivalent of vegetative M & M’s. They are high in sugar and low in lipids and proteins. It’s the latter two ingredients that are vital to providing long-term sustenance for birds attempting to overwinter in harsh climates.
If an ice storm or heavy snowfall keeps the birds from the berries, they’ll quickly find themselves in peril. A diet dominated by nonnative fruit doesn’t provide robins with adequate energy resources to ride out prolonged bouts of bad weather.