Swallows are members of the family Hirundinidae, while sparrows are part of the family Passeridae. There are about 70 swallow species, while sparrow species number more than 280. Hirundo and Tachycineta are two of the most common genus of swallow. The house sparrow (Passer domesticus) is a species generally found in North America. Although sharing appearance and name the so-called American sparrows are not true sparrows, because they are part of the family Emberizidae.
Sparrows are often slightly smaller than swallows. While sparrows range from 4 to 7 inches long and 13 to 40 g in weight, swallows can measure up to 10 inches and weigh from 10 to 60 g. Swallows also have a more elongated body and longer wings, compared with sparrows. Swallows are often dark blue to green on the back and wings, with a white or tan belly, while the predominant colors in most sparrow species are brown, light tan and yellow.
Some swallow species, especially those found in Africa and other dry-climate areas, build mud nests. North American swallows generally build their nests in cavities found in walls, caves, cliffs, abandoned buildings and hollow trees. Although sparrows can also use cavities to build their nests, they don't use mud, preferring other materials they can collect, including hay, dry grass, feathers and even hair. They also use abandoned nests from other bird species.
Although most swallows and sparrows are not in danger of extinction, more sparrow than swallow species face the risk of disappearing. Endangered swallow species include the blue swallow (Hirundo atrocaerulea); the white-tailed swallow (Hirundo megaensis); and the golden swallow (Kalochelidon euchrysea). Endangered sparrows include the Java sparrow (Padda oryzivora), native to Indonesia; the Worthen's (Spizella wortheni) and the the Sierra Madre sparrows (Xenospiza baileyi), found in Mexico; the Cuban sparrow (Torreornis inexpectata); and the salt marsh sparrow (Ammodramus caudacutus).