Eastern Bluebird

The Eastern Bluebird is an example of how grassroots conservation efforts can make a lasting impact. Back in the early and mid-1900s, bluebirds had declined due to competition with starlings and House Sparrows, both of which will aggressively exclude other birds from nesting cavities. The widespread introduction of bluebird boxes has reversed that trend, and today bluebirds are a common sight along New Hampshire’s roads and fields. Breeding numbers are roughly twice those of 50 years ago, and since the 1990s we’ve seen a dramatic increase in the winter months. At present, almost all winter bluebirds are south of the White Mountains, but this was similarly true of robins 10-15 years ago, and that species is becoming more prevalent in Coos County.

So why the winter increases? Bluebirds are susceptible to prolonged cold temperatures, and it’s no secret that our winters are getting warmer. But the steepness of the winter bluebird graphs suggests that something else might be going on, or at least acting in concert with temperature. One hypothesis is that bluebirds have benefitted from increases in ornamental fruit trees, which provide food in winter, but unfortunately we lack the data to test this hypothesis. Bluebirds also eat the fruit of invasive species like bittersweet which have been on the landscape a lot longer, so fruit availability doesn’t explain everything either. It may simply be that some combination of increased populations, warmer winters, and readily available food has led to our influx of overwintering bluebirds, and it’ll be interesting to see how this trend continues in years to come.

If you want to increase your chances of seeing bluebirds in your yard in winter, consider providing them with food such as dried mealworms (many are actually the larvae of Black Soldier Flies) and suet. They will also readily spend winter nights roosting communally in bird houses or natural cavities.