The changing natural world at our doorsteps | Illustration and text by Patterson Clark
September 7, 2010
Homebody house sparrows
By September, house sparrows have ceased breeding and are congregating in small flocks, feeding and roosting together.
Bands of juvenile birds began forming months ago after leaving the nest. They spent a few days with their father, then became independent enough to find grain, weed seeds and invertebrates on their own.
The adults, which choose one mate for the season, soon went back to breeding, raising as many as four clutches before the end of summer. Each clutch holds about five eggs.
Though juveniles may stray short distances, house sparrows are nonmigratory, stay in human-modified areas (such as cities and farms) and stick close to where they were born. Males may even choose nesting sites in the autumn, use the site for a winter roost and convert it to a nest in the spring.
The birds have been in North America since the 1850s, when 50 breeding pairs were introduced from Europe. By 1943, 150 million house sparrows had colonized the country, coast to coast.
The American landscape of the late 1800s encouraged the spread of the house sparrow. The country was dotted with small farms that supplied the cereal grains and livestock fly larvae on which the birds thrive.
Since the 1950s, pesticides have reduced insect numbers, livestock is less spread out, and grain harvest and storage is more efficient, all contibuting to an overall decline in the house sparrow population, which is falling at a rate of about 2.6 percent every year.*
Sources: Cornell Laboratory of Ornithology; "Biology of the Ubiquitous House Sparrow: from Genes to Populations," by Ted. R. Anderson.