Common name: American Robin
(Information for this Species Page was compiled by Sarah Allison for Biology 220W at Penn State New Kensington in Spring 2000)
The American robin is one of the most widely recognized birds in North America. It is often used as a size standard in the descriptions of other species of birds ("robin-sized", "smaller than a robin", etc.) and is also a symbol of the coming spring and the predictability of migration and seasonal renewal. American robins are strikingly beautiful birds with their contrasting black heads, bright yellow bills, white chins, bright red breasts, and slate gray backs. If not for their extreme abundance they would be a bird highly treasured for their appearance and their energetic songs and behaviors.
Robins are so abundant primarily because of their abilities to forage, nest, and, in general, live in almost any natural and human generated habitat. The natural habitat of the robin centered on open woodlands and forest edges. The increasing spread of human agriculture, though, provided these fruit and invertebrate foragers with an ever broadening range of potential food sources. Robins still prefer trees for nesting but will construct their nests in buildings, under porch roofs, in shrubs and even in vehicles left in one place for too long. In fact, in the spring of 2001 a female robin had a successful nest up under the roof of the Nature Trail's outdoor classroom.
Robins utilize both plant and animal food sources almost equally. Most of the preferred plant materials are fruits and especially berries. The animal materials consumed are dominantly earthworms, caterpillars, grasshoppers, spiders and grubs. The exact foods consumed by a particular individual depend upon local abundance of the food, season and, possibly, habit.
Robins are often observed on lawns and on grassy fields cocking their heads from side to side as if listening for their earthworm prey. These birds are, however, not utilizing their sense of hearing to find the worms but instead their excellent sense of vision. The robin's side-fixed eyes provide them with a very wide visual range (which is very suitable for watching out for any of the bird's abundant predators), but head cocking and bobbing is required to fix either of these eyes on the ground right in front of their beaks.
The migration behaviors of robins are some of the most widely reported and recognizable aspects of their biology. "Flying south for the winter" (south of the Canadian-U.S. border, anyway) is a very common although not universal response of this thrush to the onset of winter. The availability of food is the key to predicting the magnitude of the migrational response. Areas with abundant open soil or dense supplies of berries often have a significant percentage of their established robin populations remaining throughout the winter.
Breeding and nest building occur throughout the continental range of the robin. Nests may be established in a great variety of locations. Usually only a small, flat surface is absolutely required on which the nest is anchored. Typically nest are placed between 10 and 30 feet off of the ground although a wide range of nest locations from ground level to 75 feet up in trees have been reported. Nests are 6 inches across and 2 inches deep. They are constructed from grasses, twigs, leaves, string and a variety of other natural and man-made materials. The entire nest is then cemented together with mud. Females do almost all of the nest construction. Clutches consist of 3 to 5 baby-blue eggs which are laid at a rate of one egg per day. Incubation lasts between 11 and 14 days and is also done almost entirely by the female. The male may help to guard the nest, bring food to the female and on rare occasions actually incubate the eggs. Nestlings will fledge two weeks after birth and will become independent of their parents two more weeks after that! During fledging the adult robins may mate again and start
another clutch. Robins can have up to three clutches per year and are thus capable of very rapid reproduction.
Robins are subject to extreme predation pressures by housecats, owls and hawks. Eggs and nestlings are also preyed upon extensively by raccoons, crows, jays, squirrels, and snakes. The extreme fecundity of the species is needed to compensate for these high rates of predation. Although there may be older individuals in a population, the average life expectancy of an American robin is only one year.