Brewer's blackbirds are adapted to live in the native habitats of North America. They live in meadows, grasslands, coastal scrublands, woodlands, riparian areas, sagebrush habitats, arid landscapes, mixed chaparral forests, mountain wetlands, and more. However, Brewer's blackbirds prefer human-created habitats such as parks, agricultural fields, city streets, golf courses, and lawns - they most prefer open areas, both manmade and natural. Brewer's blackbirds build nests in colonies with other blackbirds. Females choose their nest sites and others arrive and pick areas nearby. These colonies might be found in low shrubs and treetops. Brewer's blackbirds tend to nest near water, occasionally in reeds but mostly in trees. Their nests are typically made of twigs and dried up grasses. During winter migration, Brewer's blackbirds fly in large flocks over open areas across the western and southern United States at an average elevation of about 5,400 feet (1,646 m). Migration not only includes adults but newly fledged chicks, too. (Horn, 1968; Stephen, 2002; Strassburg, et al., 2015)
Brewer's blackbirds are small, long-legged birds. They have long tails that balance their bodies and heads. Usually, adult males have tails that are much wider and rounder at the tips. Brewer's blackbirds are similar in size to American robins (Turdus americanus) and are often confused with rusty blackbirds (Euphagus carolinus). Adult males are more glossy black with a gleam of purple-blue on their heads, green iridescence on their bodies, and yellow eyes. Adult females tend to have brown bodies with darker tints on their tails and wings and dark brown eyes. Young Brewer's blackbirds are light brown and are overall a more washed out version of females. Males are larger than females, reaching sizes up to 25 cm and weighing 60 to 86 g. Females reach up to 22 cm and weigh 50 to 67 g. (Greene, 1934; Stephen, 2002)
Brewer's blackbirds are mostly monogamous but can be polygynous at times. Monogamous pairing is favored, but when there is an unbalanced sex ratio favoring females there tend to be more polygynous pairings. Polygyny in this population is likely to be strictly facultative.
Pair formation and nesting begins in late winter to early spring when food resources become more abundant. Adult female Brewer's blackbirds are attracted to songs made by males. Once paired, males will defend their mate and their nesting site. Males tend to protect colonies as a whole using guard perches.
Males and females show no apparent relationship with one another through fall and winter. However, if both individuals of a former pair are still alive the following spring, there is a probability that they will mate again. Male Brewer's blackbirds do not assist with incubating eggs and only mothers are known to incubate. Once eggs are hatched, both parents help to feed their chicks. (Cindy, 1980; Freeman, et al., 2007; Greene, 1934; Stephen, 2002)
Brewer's blackbirds usually breed between April and early May. Chicks have been found in nests until August. Females choose appropriate nesting sites and, without the help of males, build the nest. It takes 9 to 10 days for females to fully construct their nests. They build nests out of twigs and dried up grasses cemented with mud. Females then lay 3 to 7 eggs on average per season.
Once it is time to hatch, chicks have no assistance in getting out of their eggs. Only mothers incubate the eggs but both parents help to feed them and protect them from predators. Chicks remain in their nests for 12 to 16 days until they fledge. If disturbed by humans, some young ones leave as early as 9 days. Parents continue caring for their chicks until they all migrate together at the beginning of winter. After fledging, young Brewer's blackbirds associate with other immature birds and adults from several colonies. They become more independent with regards to capturing their own food and bathing themselves. Young birds cannot sexually reproduce until about a year after they are born. (Budovsky, et al., 2013; Cindy, 1980; Stephen, 2002; Thos., 1914)
Only adult female Brewer's blackbirds incubates their eggs. However, once eggs hatch, both parents feed and protect the chicks. In this way females contribute more to parental care than males. Brewer's blackbirds eat grains and seeds but hatchlings eat a good deal of insects. Parents bring food to the nest, where the young ones beg and the adults feed their chicks directly from bill to throat. Most Brewer's blackbirds are monogamous, but some polygynous populations occur in California. Where polygynous populations occur, males have to split their attention between all the nests of females with which they paired. (Powers, 1987; Stephen, 2002)
The average lifespan of Brewer's blackbirds is 11 years, but one adult male was reported to survive up to 12.5 years. In captivity, their lifespan is around 8 to 12 years. The estimated annual survivorship for males is about 38 to 54 percent while female survivorship is about 30 percent, based on capture and recovery data. (Budovsky, et al., 2013; Greene, 1934)
Brewer's blackbirds are primarily diurnal. They tend to walk, hop, and climb frequently. They normally walk with their heads bobbing on each step. When walking, they normally keep their tails low to the ground. Brewer's blackbirds fly at high altitudes, using short gliding movements once they are about to land. They do not swim, but prefer riparian areas. Adult males perform songs when near sexually active females to elicit a sort of call and response.
Brewer's blackbirds are often seen in open habitats. They are a colonial species. Females are usually aided by males in defending their territories. These territories range from 0.05 to 0.2 ha (500 to 2,000 m^2), with no overlapping areas. (Horn, 1968; Stephen, 2002)
Brewer's blackbirds forage short distances, between 1 and 500 m depending on the food resources in the area of their nests. They hunt for food on the ground in open areas. They hunt for insects while beneath bushes and shrubs or by capturing them midair. However, they mostly eat fruits and seeds. (Horn, 1968; Stephen, 2002)
Brewer's blackbirds communicate using body movements and vocalizations. Both sexes make a range of calls and songs, with most being shared. Before chicks in the egg hatch, they do not use any vocalizations. Brewer's blackbirds use multiple calls for different situations. They have warning calls, flocking calls, courtship calls, awakening calls, and more. Adults have about nine calls, but four are only used in the breeding season; the rest are used year round. When incubating females are nesting, they sometimes use a begging call to signal males to deliver food, but this is rare. (Greene, 1934; Stephen, 2002)
Brewer's blackbirds are insectivores and granivores. They also eat berries but it is very limited. When hunting for prey, they catch insects midair or by foraging on the ground. When they capture insects, they either eat them whole or pin prey with their feet to eat them piece by piece. Brewer's blackbirds eat grasshoppers (order Orthoptera, butterflies and caterpillars (order Lepidoptera), beetles (order Coleoptera), and other insects.
Brewer's blackbirds do not store their food even when they feed on a range of waste grains, oats, rice, and corn. They get grains from agricultural fields. While drinking, Brewer's blackbirds put their beaks in water while flying, then raise their heads and swallow it on wing. (Powers, 1987; Stephen, 2002)
Predators of Brewer's blackbirds include American crows (Corvus brachyrhynchos), American badgers (Taxidea taxus), black-billed magpies (Pica hudsonia), bobcats (Lynx rufus), bull snakes (Pituophis catenifer sayi), common ravens (Corvus corvax), Cooper's hawks (Accipiter cooperii), coyotes (Canis latrans), domestic cats (Felis domesticus), garter snakes (genus Thamnopis), great-horned owls (Bubo virginianus), long-tailed weasels (Mustela frenata), raccoons (Procyon lotor), ringed-bill gulls (Larus delawarensis), striped skunks (Mephitis mephitis), western rattlesnakes (Crotalus oreganus), and scrub-jays (genus Aphelocoma).
Adult birds usually give warning calls when predators are near to other birds. Usually, predators go after nestlings to feed on eggs and chicks. 63% of their predators are mammals, 32% are snakes, and 5% are other birds (Stephen, 2002).
For the most part, Brewer's blackbirds fly away to escape predators. They may strike at predators, but it is not always effective. To help reduce predation, Brewer's blackbirds make tight colonial nests and create mobbing behaviors. (Stephen, 2002)
Brewer's blackbirds have both positive and negative roles in their ecosystems. Since they are granivores, they serve both as seed predators and seed dispersers. Brewer's blackbirds eat a lot of insects so they are important in the control of their population. They eat agricultural crops, but also insects that eat crops. Not only do they affect humans, but also other wildlife. Brewer's blackbirds also serve as an important prey item for many predators. The majority of their predators include mammals, snakes, and birds.
In general, human activities have created places for Brewer's blackbirds to live. Many people enjoy seeing Brewer's blackbirds and listen to their songs as they chirp. Brewer's blackbirds contribute to a diverse community of animals within their habitats. (Greene, 1934; Thos., 1914)
Brewer's Blackbirds are effective to control insect pest populations. They eat a variety of insects during summer crop growing seasons as well as during non-breeding periods. Brewer's blackbirds help to control pests to not overpopulate and ruin crops. (Stephen, 2002)
Some humans believe that Brewer's blackbirds are inconvenient to have around human-created habitats. These birds are always around buildings and other structures near humans. They also carry diseases such as avian salmonellosis. This is due to environmental contamination and is an issue in suburban and urban areas, where people set up bird feeders. Brewer's blackbirds are likely to be influenced and are natural hosts to mosquito-borne viruses like St. Louis encephalitis and western equine encephalitis. These viruses are pathogens for humans and can cause morbidity and mortality.
Brewer's blackbirds cause damage by foraging from crops. Farmers have lost agricultural products in fall and winter. While the extent of the losses is unknown for most of the United States, Brewer's blackbirds in Tennessee have eaten 2% of grain distribution. In 1980, they reduced sunflower production by 2% in Minnesota, South Dakota, and North Dakota. In these states, it is where most United States sunflower fields are located. Due to this tragedy, farmers are poisoning crops against Brewer's blackbirds to stop them from eating crops. (Greene, 1934; Stephen, 2002)
Brewer's blackbird populations are usually stable, but have been declining by about 2% each year. This has multiple causes, including shooting, poisoning crops, and collisions with windows of buildings. Migratory movements appear to occur during daylight periods so collisions have been reported. Another factor would be reductions in their food supplies.
Despite these impacts, Brewer's blackbirds continue to be widespread throughout the United States. Even though they are decreasing they can be found outside homes, parks, cities, etc.. Brewer's blackbirds are protected by the U.S. Migratory Bird Act. They are of least concern on the IUCN Red List and have no special status on the U.S. Federal List, CITES, or the State of Michigan List. (Stephen, 2002)
Shannon Lopez (author), California State University, San Marcos, Tracey Brown (editor), California State University, San Marcos, Galen Burrell (editor), Special Projects.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
uses sound to communicate
living in landscapes dominated by human agriculture.
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
either directly causes, or indirectly transmits, a disease to a domestic animal
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
uses smells or other chemicals to communicate
to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
helpers provide assistance in raising young that are not their own
to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
marshes are wetland areas often dominated by grasses and reeds.
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
having more than one female as a mate at one time
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
specialized for leaping or bounding locomotion; jumps or hops.
scrub forests develop in areas that experience dry seasons.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.
living in residential areas on the outskirts of large cities or towns.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.
living in cities and large towns, landscapes dominated by human structures and activity.
uses sight to communicate
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Cindy, P. 1980. An Experimental Study of Parental Investment and Polygyny in Male Blackbirds. The American Society of Nationalist, 116/6: 757-769.
Freeman, S., D. Noble, S. Newson, S. Baillie. 2007. Modeling Population Changes Using Data from Different Surveys: The Common Birds Census and the Breeding Bird Survey. Bird Study, 54: 61-72.
Greene, E. 1934. Brewer's Blackbird (Euphagus cyanocephalus) in Georgia. The Auk, 51.1: 91.
Horn, H. 1968. The Adaptive Significance of Colonial Nesting in the Brewer's Blackbird (Euphagus Cyanocephalus). Ecological Society of America, 49/4: 682-694.
Power, D. 1971. Range expansion of Brewer's blackbird: phonetics of a new population. Canadian Journal of Zoology, 49/2: 175-183.
Powers, L. 1987. Brewer' Blackbird Feeding on a Barn Swallow. The Wilson Bulletin, 99.2: 294-295.
Stephen, M. 2002. "Brewer's Blackbird (Euphagus cyanocephalus)" (On-line). In the Birds of North America. Accessed February 18, 2020 at https://birdsna.org/Species-Account/bna/species/brebla/introduction.
Strassburg, M., C. Shawn, L. George. 2015. Winter habitat associations of blackbirds and starlings wintering in the south-central United States. Human-Wildlife Interactions, 9/2: 171-179.
Thos., R. 1914. Brewer's Blackbird (Euphagus cyanocephalus) Breeding in Southeastern Minnesota. The Auk, 31.4: 538-540.
Unitt, P. 2004. San Diego County Bird Atlas. San Diego: Sunbelt Publications.