Brewer's Sparrow Life History

Habitat

Habitat ScrubBrewer’s Sparrow is one of only a handful of “sagebrush obligate” bird species (including Sage Thrasher, Sagebrush Sparrow, and the two species of sage-grouse: Greater and Gunnison). Brewer’s Sparrows depend almost exclusively on the sagebrush ecosystem when breeding. This mostly treeless habitat covers an immense area of the arid West, and is found nowhere else. It tends to be dominated by big sagebrush (Artemisia tridentata) and similar species that grow up to about 5 feet tall, interspersed with bunchgrasses and bare ground. Some Brewer’s Sparrows also use large clearings in pinyon-juniper woodlands, which share similar vegetation with the traditional sagebrush steppe. The northern subspecies (aptly called “Timberline Sparrow”) breeds at high elevations, where dense and tall vegetation gives way to the dwarf willow and birch shrubs of alpine valleys. During winter, Brewer’s Sparrows (of both subspecies) occupy sagebrush shrublands similar to the breeding grounds, as well as a range of desert scrub habitats consisting mainly of saltbush and creosote.Back to top

Food

Food InsectsBrewer’s Sparrows eat mostly small insects during the breeding season, including caterpillars, leaf beetles, weevils, grasshoppers, ants, and other insects and spiders. Less is known about what they eat on their wintering grounds, but they probably eat a greater proportion of seeds. They glean insects from bark and foliage of shrubs and they pick up seeds from the ground. During the breeding season, adults spend up to three-quarters of their foraging time in shrubs, as opposed to on bare ground or at the base of bunchgrasses between shrubs. Back to top

Nesting

Nest Placement

Nest ShrubBrewer’s Sparrows choose tall and densely branching shrubs (most often big sagebrush, Artemisia tridentata) for nesting. They place their nests just outside the shrub’s densest parts. Compared to the landscape as a whole, the immediate area surrounding nests tends to have more sagebrush cover and less bare ground and grass cover. They build their nests safely below the top of the sagebrush shrub but only rarely nest lower than 8 inches off the ground.

Nest Description

Females do most of the nest-building, taking 4 to 5 days to build their first nest of the season and as little as 2 days for subsequent nests. The nest is a small cup of dry grasses, with the outermost layer sometimes composed of sagebrush twigs. The cup interior made of fine grasses, sagebrush bark, and sometimes hair. Nests measure roughly 3.5 inches across, and the cup diameter is about 2 inches.

Nesting Facts
Clutch Size:2-5 eggs
Number of Broods:1-2 broods
Egg Length:0.6-0.7 in (1.6-1.7 cm)
Egg Width:0.5-0.5 in (1.2-1.3 cm)
Incubation Period:10-12 days
Nestling Period:6-9 days
Egg Description:Blue-green, spotted with dark brown or reddish brown.
Condition at Hatching:Naked except for sparse tufts of light gray natal down.
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Behavior

Behavior Foliage GleanerMales arrive on breeding grounds several days before females, and sing from prominent perches to establish and defend breeding territories. Pairs appear to be monogamous but, as with many birds, they may mate with neighbors covertly. Perhaps to minimize this chance, males accompany their mates and aggressively chase away interlopers prior to egg-laying). Males sometimes offer food to their mates during early pair formation. Females soliciting this courtship feeding droop and quiver their wings, and sometimes utter a soft twittering call. After nests are built, males remain in the immediate vicinity, alternating between foraging within shrubs and singing atop them. Larger Sagebrush Sparrows and Sage Thrashers with overlapping territories will displace Brewer’s Sparrows from singing perches; however, Brewer’s Sparrows will also join these species to mob and chase small mammalian nest predators. Both parents handle the work of incubation and caring for young, though the female does more of the work. In winter, Brewer’s Sparrows form mixed-species flocks with other sparrows, particularly others in the Spizella genus. Predators include gopher snakes, rattlesnakes, chipmunks, long-tailed weasels, Common Ravens, Black-billed Magpies, Loggerhead Shrikes, and American Kestrels. Back to top

Conservation

Conservation Low ConcernThe Brewer’s Sparrow remains the most abundant bird of the sagebrush ecosystem, however, populations declined by about 49% between 1966 and 2014, according to the North American Breeding Bird Survey. Partners in Flight estimates the global breeding population at 13 million with 99% spending some part of the year in the U.S., 1% breeding in Canada, and 60% wintering in Mexico. They rate a 12 out of 20 on the Conservation Concern Score. They are a U.S.–Canada Concern Species; they are not on the 2014 State of the Birds Watch List. As with other sage-dependent birds, concerns include habitat degradation and fragmentation throughout the intermountain West of North America. In the sagebrush ecosystem, threats include livestock grazing, residential and energy development, agricultural conversion, and invasive species such as cheatgrass, which alters the natural fire regime. Back to top

Credits

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

North American Bird Conservation Initiative. 2014. The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Rotenberry, J. T., Michael A. Patten and K. L. Preston. 1999. Brewer's Sparrow (Spizella breweri), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, Jr. Ziolkowski, D. J. and W. A. Link. The North American Breeding Bird Survey, results and analysis 1966-2013 (Version 1.30.15). USGS Patuxtent Wildlife Research Center 2014b. Available from http://www.mbr-pwrc.usgs.gov/bbs/.

Sibley, D. A. (2014). The Sibley guide to birds, second edition. Alfred A. Knopf, New York, USA.

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