American Robin

The American Robin is clearly one of the most familiar birds in North America. Unlike other contenders like cardinals, bluebirds, and chickadees, it occurs across the continent from arctic Alaska to the mountains of southern Mexico. Populations north the southern Canada are migratory, and shift into the United States as winter progresses, while some in southern mountains areas move downslope into the deserts of the southwest. In the east, robins are rare breeding birds in states bordering the Gulf of Mexico but can be exceptionally abundant here in winter. Here in New Hampshire, while robins have traditionally been considered a sign of spring, their abundance as an overwintering bird began to increase in the 2000s, and they are now found year-round except in much of Coos County and the White Mountains.

This subtle range shift is testament to the robin’s adaptability. While historically a species of forests and forest edges, robins quickly took to human-altered habitats. It is one of only a handful of birds that readily nest directly on buildings (e.g., gutters and porch lights) and even nests on the ground in some areas. Robin nests are easy to recognize by the layer of mud between the outer layer of grass and the lining of finer materials, and if in a well-sheltered space will persist in good condition through the winter. Sometimes nests will be re-used for subsequent broods within a season. With a warming climate, robins in New Hampshire are breeding earlier and earlier, and in some parts of the state three broods are increasingly common.

Robins are famous for their hunting of earthworms, but these are not native to most of New England. All the earthworms we have in New Hampshire are invasive species from Europe that can have negative effects on forest ecosystems. Presumably robins foraged primarily on native insects and their larvae prior to European colonization. In fall and winter, robins shift their diet from invertebrates to fruit, and start to form large flocks that wander across the landscape in search of both native and ornamental fruiting shrubs and trees. Increases in non-native species such as crab apples may be part of the explanation for robins wintering farther north, although climate change is also likely a factor.

Despite their adaptability, robins have started to show signs of decline across much of their range, usually starting in the 1990s or early 2000s. Although populations in New Hampshire are stable, those in neighboring states and provinces have dropped by 20-40 percent since 2000 and there are no clear explanations. Habitat change is an unlikely threat, leaving us with poorly known stressors such as pesticides, disease, and maybe even invasive species. Perhaps research on a common species like the American Robin can help conservation biologists better understand these emerging threats in time to help numerous other declining bird species.