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NATURAL HISTORY

TRICOLORED BLACKBIRD } Agelaius tricolor
FAMILY: Icteridae

DESCRIPTION: The tricolored blackbird is medium sized, ranging in length from seven to nine inches and weighing two to three ounces. Adult males are larger than females and have a pitch-black body with a brownish-red and white patch on their wing shoulders. Adult females are mostly black with grayish streaks, a whitish chin and throat, and small but distinct reddish shoulder patches. Juveniles of both sexes look similar to adult females, but are much paler in color.

HABITAT: The tricolored blackbird prefers wetland and grassland habitats, although most native habitats have been lost. Within the Central Valley, breeding colonies live in the rice-growing regions of the Sacramento Valley and in the pasturelands of the lower Sacramento Valley and San Joaquin Valley. Colonies outside the Central Valley inhabit a wide variety of habitat types, including chaparral-covered hills, orange and avocado groves interspersed with grass-covered hills, sagebrush grasslands, and salt-marsh habitat. Nesting takes place in native emergent marshes, silage and other grain fields, thickets of the introduced Himalayan blackberry, and other flooded and upland habitats.

RANGE: The historical breeding and winter range of the tricolored blackbird in California included the Central Valley and low foothills of the Sierra Nevada, from Shasta County south to Kern County, along the coast from Sonoma County to the Mexican border, and occasionally on the Modoc Plateau.  A study done in the 1990s indicated that despite reductions in colony size and numbers, the bird’s distribution has not changed dramatically since the 1930s. However, there are no surveys dating from before most of central California’s wetlands were lost.

MIGRATION: Tricolored blackbirds breeding in Oregon fly south for the winter; birds breeding in California stay in the state all year. Tricolors are nomadic but have relatively small territories.

BREEDING: Tricolors breed in the spring in dense colonies, engaging in “prospecting behavior” in which concentrations of birds will gather and suddenly fly to another place, changing locations frequently and then returning to potential nesting sites. These birds exhibit itinerant breeding, with individuals often moving after their first nesting attempts to breed again at a different location. Males mate with one to four females per year; they do not assist with nest construction or egg incubation but do help gather food and feed young. Within a colony, eggs are all laid in the same week, with each nest averaging three to four eggs. Eggs incubate for 11 or 12 days and young leave the nest about two weeks after hatching.

LIFE CYCLE: Data suggest that tricolors live for at least 13 years.

FEEDING: Tricolors are opportunistic foragers, eating any locally abundant insects including grasshoppers, beetles and weevils, and the larvae of caddis flies, moths and butterflies, and dragonflies. The birds will also eat grains, snails, and small clams. They forage in all seasons in pastures, dry seasonal pools, agricultural fields, scrub, and the borders of marshlands and grasslands.

THREATS: The widespread loss of native marshes and wetlands to land conversions for vineyards, orchards, and urban development have threatened the very survival of the tricolored blackbird. Predation is rampant in the bird’s little remaining native habitat.

POPULATION TREND: The population of tricolored blackbirds in the Central Valley declined by at least 50 percent between the 1930s and early 1970s, and an additional decline of about 56 percent of the remaining population was reported from 1994 to 2000. Population censuses indicate that the tricolor declined from an estimated 370,000 in 1994 to 240,000 in 1997 and 162,000 in 2000.