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blue grosbeak

Passerina caerulea

What do they look like?

Blue grosbeaks are large buntings; they are usually 15 to 16 cm long and weigh about 26 to 31 g. Male blue grosbeaks are much more colorful than females, with bold purplish blue plumage. Males have black flight feathers and two brown wingbars. Male blue grosbeaks also have a silvery lower beak and a black upper beak, with a strip of black extending from their upper beak to their eye. Females are mostly brown, and sometimes have a few blue feathers on their head and wings. Their wings are mostly black with two light brown wingbars. Their breast feathers tend to be a slightly lighter brown than the rest of their body. Males and females of this species tend to be about the same size. Blue grosbeaks are larger than other closely related species such as lazuli buntings and indigo buntings. (Gough, et al., 2000; Lockwood, 2007; Lowther and Ingold, 2011)

  • Sexual Dimorphism
  • male more colorful
  • Range mass
    26 to 31 g
    0.92 to 1.09 oz
  • Range length
    15 to 16 cm
    5.91 to 6.30 in

Where do they live?

Blue grosbeaks (Passerina caerulea) are small birds that migrate each year. In early April, these birds migrate to the southern United States. Their northern border includes southern California, Nevada and Utah, as well as Colorado, South Dakota, southern Missouri, Kentucky, parts of southern Illinois, Indiana, Ohio, Virginia and Massachusetts. Some blue grosbeaks have even been seen as far north as Idaho. In the south, they are often seen throughout Texas. In mid-October, after their breeding season, blue grosbeaks migrate to their winter location in Mexico and the Caribbean Islands. In some parts of Central Mexico, they are permanent residents and do not migrate. (Gough, et al., 2000; Lockwood, 2007; Powers, 1971)

What kind of habitat do they need?

Blue grosbeaks are usually found in open areas with shrubs, brush and small trees, at the edges of woodlands, or sometimes in grasslands. In any of these habitats, blue grosbeaks choose areas with fewer trees. In their wintering areas, blue grosbeaks usually live in and on the edges of dry, tropical forests and in bushy shrubs. (Lockwood, 2007; Lowther and Ingold, 2011; Peterson, 2009)

How do they reproduce?

Blue grosbeaks breed from early April to late August. Males probably arrive on the breeding grounds before females. These birds probably breed in monogamous pairs; this is based on sightings of the same paired individuals multiple times per mating season. Little is known about their courtship behavior, but males guard their females by following closely as they feed. (Bent, 1968; Hicks, 1945; Lowther and Ingold, 2011; Risch and Robinson, 2006; Stabler, 1959)

Female blue grosbeaks build their cup nests about 1 to 4 m (3 to 10 feet) above the ground. Blue grosbeaks build two nests and have two broods each year. Their first nest is usually built in May and their second nest is typically built in August. Each clutch usually includes 3 to 5 eggs. Their eggs are pale blue to bluish-white with occasional brown spotting. Males feed the females during the 11 to 12 day incubation period. The chicks are ready to start flying about 9 to 10 days after hatching. (Bent, 1968; Lowther and Ingold, 2011; Risch and Robinson, 2006; Stabler, 1959)

  • How often does reproduction occur?
    Blue grosbeaks breed twice yearly.
  • Breeding season
    These birds breed from April to August.
  • Range eggs per season
    3 to 5
  • Range fledging age
    9 to 10 days

In their monogamous breeding system, both parents care for their young. After the chicks hatch, they are fed by both parents. When the female begins building her second nest, the male spends more time caring for the chicks. (Lowther and Ingold, 2011)

How long do they live?

There is little information available on the lifespan of blue grosbeaks. However, the longest documented lifespan for this species is 5 years and 11 months. (Lowther and Ingold, 2011)

  • Range lifespan
    Status: wild
    5.9 (high) years

How do they behave?

Males begin flocking and feeding in their breeding grounds before females arrive in the spring. During breeding season, the condition of the male's feathers helps to indicate his quality and females use this information when selecting a mate. During the summer months, flocks of males and females feed together. While foraging, they may hop awkwardly, but are more commonly seen flying low over the ground. Mating pairs are often seen together, and males follow the females very closely. This species is very shy around humans, which makes observing them very difficult. Both males and females flick their tail often, although the purpose of this behavior is unknown. Blue grosbeaks have also been known to sidle, or walk sideways along branches, as seen in parrots. (Keyser and Hill, 2000; Lowther and Ingold, 2011; Peterson, 2009; Stiles and Skutch, 1989)

  • Range territory size
    6000 to 61900 m^2
  • Average territory size
    52600 m^2

Home Range

Blue grosbeaks have a territory size of 6,000 to 61,900 meters squared (0.6 to 6.19 hectares). Larger males with more intense blue coloration tend to have larger territories. (Grubb, 2006; Harris and Wallace, 1984; Odum and Kuenzler, 1955)

How do they communicate with each other?

Only male blue grosbeaks are known to sing. Their song is a long, rich warble that lasts about 2.5 seconds. Their songs do not have the 'burry' sound common in related species, such as house finches and indigo buntings. The beginning of their song is usually similar between males, but the end of the song can be different. Older males tend to have longer songs. Their songs become more complex when females are looking for mates. Their flight call is described as 'zit-zit-zu-zit-zit-zu zoo-zieet zieet zieet zi-zi-zi-zi-zi-zi-zi-zi'. Their general call is described as a low-pitched buzz or a metallic tink. During mating periods, females may keep the feathers on their crown upright. Both males and females often spread or flick their tails, although the purpose of these movements is unknown. Most of the male's colors are not visible to the human eye. Male coloration indicates their quality and is related to female mate choice. (Ballentine, et al., 2003; Bent, 1968; Keyser and Hill, 2000; Lattin and Ritchison, 2009; Lowther and Ingold, 2011)

What do they eat?

Blue grosbeaks gather most of their food by foraging in agricultural fields and pastures. In the fall, blue grosbeaks often gather in large flocks to feed in grain fields. They eat mostly invertebrates including snails, beetles, moths, grasshoppers, spiders and worms. Blue grosbeaks also eat seeds, especially grass and waste grain in abandoned agricultural fields. When feeding insects to their young, the adults remove the head, legs and wings. (Lowther and Ingold, 2011; Peterson, 2009)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • terrestrial worms
  • Plant Foods
  • seeds, grains, and nuts

What eats them and how do they avoid being eaten?

There is no information on predators of this species, aside from general bird predators such as raptors as well as snakes and cats. (Lowther and Ingold, 2011; Risch and Robinson, 2006)

  • Known Predators
    • raptors
    • snakes
    • cats

What roles do they have in the ecosystem?

The nests of blue grosbeaks are parasitized by brown-headed cowbirds, which lay their eggs in blue grosbeaks' nests. Blue grosbeaks may also have feather mites from genus Proctophyllodes. They may help spread diseases between birds and mosquitoes, as their range is expanding northward where there are a growing numbers of diseases. (Epstein, et al., 1998; Gardner, et al., 2008; Lowther and Ingold, 2011; Molaei, et al., 2006; Peterson, 2009; Risch and Robinson, 2006)

  • Ecosystem Impact
  • disperses seeds
Commensal or parasitic species (or larger taxonomic groups) that use this species as a host
  • brown-headed cowbirds (Molothrus ater)
  • feather mites (Proctophyllodes)

Do they cause problems?

Other small birds are known to carry diseases; however, blue grosbeaks are not currently known to carry any diseases. (Lockwood, 2007)

How do they interact with us?

Because these birds are so shy, there is very little information about their interactions with humans. Blue grosbeaks mostly eat insects, so they could help control pest insect populations. (Lowther and Ingold, 2011; Peterson, 2009)

  • Ways that people benefit from these animals:
  • research and education

Are they endangered?

The summer breeding range of blue grosbeaks is expanding northward and their population is stable and even increasing slightly. Their conservation status is considered of “Least Concern”, which means they are in no danger of extinction in the near future. Blue grosbeaks avoid suburban areas. As with many birds, increasing development could lead to population decreases. However, their habitats, especially abandoned agricultural fields, are plentiful at this point. (Butchart and Symes, 2012; Peterson, 2009)

Contributors

Lauren Smith (author), Northern Michigan University, Alec Lindsay (editor), Northern Michigan University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

References

Ballentine, B., A. Badyaev, G. Hill. 2003. Changes in Song Complexity Correspond to Periods of Female Fertility in Blue Grosbeaks (Guiraca Caerulea). Ethology, 109.1: 55-66.

Bent, A. 1968. Life histories of North American cardinals, grosbeaks, towhees, finches, sparrows, and allies (Part 1). Washington, D.C: Smithsonian Institution Press.

Butchart, S., A. Symes. 2012. "Passerina caerulea" (On-line). The IUCN Red List of Threatened Species. Accessed March 01, 2013 at http://www.iucnredlist.org/details/22723939/0.

Epstein, P., H. Diaz, S. Elias, G. Grabherr, N. Graham, W. Martens, E. Mosley-Thompson, J. Susskind. 1998. Biological and Physical Signs of Climate Change: Focus on Mosquito-borne Diseases. American Meteorological Society, 79/3: 409-417.

Gardner, C., C. Burke, M. Tesfay, P. Glass, W. Klimstra, K. Ryman. 2008. Eastern and Venezuelan Equine Encephalitis Viruses Differ in Their Ability To Infect Dendritic Cells and Macrophages: Impact of Altered Cell Tropism on Pathogenesis. Journal of Virology, 82/21: 10634-10646.

Gough, G., J. Sauer, M. Iliff. 2000. "Patuxent Bird Identification Infocenter" (On-line). Accessed February 13, 2013 at http://www.mbr-pwrc.usgs.gov/id/framlst/infocenter.html.

Grubb, T. 2006. Ptilochronology: Feather Time and the Biology of Birds. New York: Oxford University Press.

Harris, L., R. Wallace. 1984. Breeding bird species in Florida forest fragments. Proceedings of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies, 38: 87-96.

Hicks, L. 1945. Blue Grosbeak Breeding in Ohio. The Auk, 62.2: 314.

Keyser, A., G. Hill. 2000. Structurally Based Plumage Coloration Is an Honest Signal of Quality in Male Blue Grosbeaks. Behavioral Ecology, 11.2: 202-209.

Lattin, C., G. Ritchison. 2009. Intra- and Intersexual Functions of Singing by Male Blue Grosbeaks: The Role of Within-Song Variation. The Wilson Journal of Ornithology, 121/4: 714-721.

Lockwood, M. 2007. Basic Texas Birds: A Field Guide. Austin, Texas: University of Texas Press.

Lowther, P., J. Ingold. 2011. "Blue Grosbeak (Passerina caerulea)" (On-line). The Birds of North America Online. Accessed December 17, 2013 at http://bna.birds.cornell.edu.proxy.lib.umich.edu/bna/species/079/articles/introduction.

Molaei, G., J. Oliver, T. Andreadis, P. Armstrong, J. Howard. 2006. Molecular Identification of Blood-meal Sources in Culiseta Melanura and Culiseta Morsitans from an Endemic Focus of Eastern Equine Encephalitis Virus in New York. The American Journal of Tropical Medicine and Hygiene, 75/6: 1140-1147.

Odum, E., E. Kuenzler. 1955. Measurement of Territory and Home Range Size in Birds. The Auk, 72/2: 128-137.

Peterson, R. 2009. "Blue Grosbeak" (On-line). Peterson Field Guides. Accessed February 13, 2013 at http://www.houghtonmifflinbooks.com/peterson/resources/identifications/blgr/index.shtml.

Powers, L. 1971. Blue Grosbeak in Idaho. The Murrelet, 52.2: 26.

Risch, T., T. Robinson. 2006. First Observation of Cavity Nesting by a Female Blue Grosbeak. The Wilson Journal of Ornithology, 118.1: 107-108.

Stabler, R. 1959. Nesting of the Blue Grosbeak in Colorado. The Condor, 61.1: 46-48.

Stiles, F., A. Skutch. 1989. A Guide to the Birds of Costa Rica. Ithaca, NY: Cornell University Press.

Whitmore, R. 1977. Habitat Partitioning in a Community of Passerine Birds. The Wilson Bulletin, 89.2: 253-265.

 
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Smith, L. 2014. "Passerina caerulea" (On-line), Animal Diversity Web. Accessed September 21, 2018 at http://www.biokids.umich.edu/accounts/Passerina_caerulea/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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