The following biological profile was provided by Ted Beedy.
The tricolor is a medium-sized, sexually dimorphic blackbird. Adult males are glossy black, often with an iridescent blue-green sheen in bright sunlight. Adult females are dark brown with dark gray and brown streaks, with bellies more consistently dark brown than in the very similar female red-winged blackbird (Agelaius phoeniceus). Young females lack an epaulet, but with age an orange-red epaulet develops. Juveniles are similar to females but paler (Pyle 1997). Adult male epaulets are typically bright scarlet and distinguishable from the red-orange epaulet of the adult male red-winged blackbird. Band below epaulet bright white, not yellow or gold as in the red-winged blackbird. Breeding males average 60-65 grams and breeding females average 40-45 grams. Total body length is 18-24 cm.
Bills of both sexes long, narrow, round, and pointed (Beedy and Hamilton 1999). Both sexes have narrow, pointed wings with primary 9 longer than primary 6 (Mailliard 1910, Pyle 1997), giving the bird in flight a more pointed-wing profile than the closely related red-winged blackbird and enabling experienced observers to distinguish tricolors from other blackbird species at a distance (Mailliard 1910, Orians 1961). Flight typically undulating, and foraging flocks tend to be compact and linear.
Often silent in flight, but may emit a distinctive "wuk" call (Collier 1968); much lower in frequency than red-wing (Orians and Christman 1968). During the early breeding season, males typically utter a strange mewing call very unlike other blackbirds and a loud song chorus is characteristic of settlements and establishing colonies.
There are no identified subspecies, although the tricolored blackbird has two distinct population segments: a Southern California population that occurs in southern California south of the Tehachapi Mountains and into northern Baja California, and a Central Valley population segment that occurs throughout the Central Valley. Banding studies involving in excess of 70,000 birds have detected a mere trickle of individuals that move between these population segments, with a total of only 3 birds known to have moved from one population segment to the other.
Historical Breeding Distribution
Formerly abundant both in coastal California, where it was considered the most abundant bird from Los Angeles to San Diego in the mid-19th Century (Cooper cited in Baird and Cooper 1859), and in the Central Valley of California through interior southern California to northern Baja California (Grinnell 1915). Reported to breed in small numbers in southern Oregon (Neff 1937).
Current Breeding Distribution
Since 1980, breeding has occurred in 46 California counties (Beedy and Hamilton 1999), although the species has essentially been extirpated as a breeder in coastal locations (Kelsey 2008) and persists in very small numbers (5,500 in 2008; Kelsey 2008) at scattered sites in southern California (Unitt 2004, Kelsey 2008). Gaps also occur in the breeding distribution in the Central Valley (e.g., Meese 2006, 2007; Kelsey 2008). Small colonies of tens of individuals persist in northern Baja California (Erickson et al. 2007, 2008), a single colony of fewer than 30 individuals breeds in western Nevada (Ammon and Woods 2006), formerly up to two thousand birds breed at several scattered sites in Oregon (Marshall et al. 2003), and since 1998 a few tens of birds have bred in several locations in Washington (Wahl et al. 2005).
Withdraws from Washington, Oregon and Nevada as well as from Baja California. Also withdraws from coastal regions of Santa Barbara and San Diego Counties and portions of northern California outside of the Central Valley. Wintering populations concentrate in the Sacramento-San Joaquin Delta and the central coast, particularly in Monterey, Marin, Sonoma and Santa Cruz counties, where they occur in multispecies flocks with other blackbirds, brown-headed cowbirds, and European starlings (Beedy and Hamilton 1999). Wintering tricolors are associated with open rangeland in the Sacramento-San Joaquin Delta and along the central California Coast, often near diaries. From mid-October to February flocks to 25,000 frequent dairies on the outer Point Reyes Peninsula in Marin County (Beedy and Hamilton 1999), but no birds have been seen during winter there since 2012 (Meese, pers. obs.). A wintering population estimated at 50,000 birds was observed by Ted Beedy and Bob Meese outside Birds Landing, Solano County in late October, 2007 but fewer than 1,000 tricolors were observed wintering in the same location in winter 2015/2016 (Meese, pers. obs.).
The precise locations of and habitats utilized by wintering tricolors are poorly known and there is great need for extensive study of the distribution and abundance of this species throughout the winter.
Often described as nonterritorial, but both males and females maintain breeding territories held for the duration of a single nesting effort. Territories are compressed and include only nesting space, not foraging areas. The range in the sizes of territories is less than one to several square meters, with most territories between 2 and 6 square meters (Beedy and Hamilton 1999). In some instances, especially in especially high nest densities, tricolor territories may be vertically stacked (e.g., Hamilton and Meese 2005).
In contrast, the closely-related red-winged blackbird is highly territorial and during the breeding season males defend territories that include two to several females as well as some foraging habitat. Thus, red-winged blackbirds are quite sparsely distributed across the landscape during the breeding season while tricolored blackbirds tend to form large, dense colonies during the breeding season and it is this difference in behavior that most clearly distinguishes the two species for most people.
Males arrive on the breeding sites 1-3 days before the females, typically in mid-to-late March in southern California and the San Joaquin Valley (DeHaven 1975b). The tricolor typically nests twice, and the second breeding attempt often occurs in a different, more northerly location (Hamilton 1998), although when breeding conditions permit, second breeding attempts may occur in the same or immediately adjacent locations (Meese 2006, 2007, 2008). Comparable movements have not been reported in southern California, where the bird is believed to be resident.
In most cases, one male breeds with two females in each breeding attempt. It is believed that the pair bond persists for one breeding attempt, and that second breeding attempts occur among different individuals, although this has not been definitively established. Tricolors are site-faithful, and if landscape conditions permit, will return to breed in the same locations year after year (Meese, unpub. data).
The tricolor builds its nests on a variety of substrates, although most of these are either flooded or armored. Historically, most colonies were established in freshwater marshes dominated by cattails (Typha spp.) and bulrushes (Scirpus or Schoenoplectus spp.), with willows (Salix spp.) and nettles (Urtica spp.) also common (Neff 1937). The introduced mustards (Brassica spp.), blackberries (Rubus spp.), thistles (Circium spp.), and mallows (Malva spp.) have been commonly used for several decades.
Since the 1980's, the largest colonies have formed in grain (almost exclusively triticale, a hearty wheat x rye hybrid) fields in the San Joaquin Valley, especially so-called "dirty fields" that have relatively large amounts of invasive mustards or mallows.
The tricolor builds an open cup nest out of long leaves of a variety of plants. In most cases, the leaves are collected dry, then taken to a nearby water source, placed in the water for several seconds until thoroughly wet, and then taken to the nest site (Meese, pers. obs.). The leaves are woven around stout, upright stems of many plants species, and at heights of only a few cm to 2 meters above ground or water level, with ca. 1 meter being typical. The female builds the nest alone, with males only very rarely providing nest materials to the females. Nest-building takes about 3 days. Coarse materials are woven around the stems to produce a platform, then similar materials are used to create the sides, a mud bottom is added, and when this dries, very fine materials are placed on top of the mud to provide a soft substrate for the eggs.
Typically, four eggs are laid, with 3-egg clutches also common (the most common number for second clutches in a season), and 5-egg clutches rare. The eggs are oval, typically light blue but occasionally light green, with dark reddish-brown splotches concentrated on one end. Egg length averages 24-25 mm, and egg weight averages 2.5-5 grams. Egg laying typically begins the day after nest completion, and one egg is laid per day (Beedy and Hamilton 1999).
Incubation of eggs is exclusively by the females and begins with the laying of the first egg (Beedy and Hamilton 1999). Eggs are incubated for approximately 12 days, exceptionally to 14 days (Payne 1969).
Nestling Growth and Development
The young are born naked and blind. Young weigh 2-3 grams at birth (Beedy and Hamilton 1999). Nestlings typically fed for 11-12 days; feeding by both parents. Young fed almost exclusively animal prey from birth until day 9, after which a mixture of both plant and animal foods are provided (Crase and DeHaven 1977; Skorupa, Hothem, and DeHaven 1980; Meese pers. obs.).
Young typically fledge at day 10-14. Fledglings remain in or on periphery of colony for several days post-fledging, actively and quite vocally soliciting food from adults. Both parents feed fledglings. In many cases, adults lead fledglings away from the colony by returning to the fledgling with food, but instead of feeding the fledgling, fly away from the colony with the fledgling in pursuit.
Diet and Foraging
Tricolored blackbirds, like other blackbird species, are fundamentally granivores (Orians 1980); however, tricolors consume a wide variety of plant and animal foods (Skorupa, Hothem, and DeHaven 1980), and respond opportunistically to the most abundant, readily available food resource. In the San Joaquin Valley, most tricolors feed on stored grains associated with dairies, with additional animal foods taken from both aquatic and terrestrial habitats up to 9 km from the colony. Birds may forage over a wide area, but females forming eggs and adults feeding nestlings typically concentrate foraging efforts on small, highly productive habitats, including shrublands (often excellent sources of caterpillars), pasturelands (many types of insects, but especially grasshoppers during grasshopper "breakout" years), wetlands (aquatic insect larvae), and rice paddies (aquatic insect larvae).
Sources of Mortality
Exposure to severe weather can cause massive mortality to adult females, eggs, and nestlings (Beedy and Hamilton 1999, Meese pers. obs.). Intense rainfall and strong winds are the two primary weather-related mortality sources, but colony desertion may occur after day 3 of a mid-summer heat wave where daytime temperatures exceed 38C (100F) for three or more days in a row (Meese, pers. obs.). The tricolor has a large number of predators, and predation has been implicated in colony desertion (Beedy and Hayworth 1992, Hamilton 1998, Hamilton and Meese 2005). The most serious tricolor predators are black-crowned night herons (Nycticorax nycticorax) and white-faced ibises (Plegadis chihi; video by Kelly Weintraub) and raccoons (Procyon lotor) in wetland colonies and coyotes (Canis latrans) and cattle egrets (Bubulcus ibis; Meese 2011) in upland and triticale colonies. Additional predators include northern harriers (Circus cyaneus), northern ravens (Corvus corax), Cooper's hawks (Accipiter cooperii; Beedy and Hamilton 1999), and California king snakes (Lampropeltis getula), as illustrated in the video above, taken by Irene Liu, a Duke University graduate student, at the Conaway Ranch in Yolo County in June, 2013.
Demographic information is only now becoming available as until recently relatively few banded birds have been recovered to make generalizations. Work by Neff (1942) and DeHaven and Neff (1973) suggests a maximum lifespan of at least 12 years, while Kennard (1975) suggests a 13 year lifespan. These are most likely to maxima for males, as they are about 50% larger than females and likely live longer. Band returns analyzed by Meese (unpub. data) suggest an average annual adult survivorship of 60%.
Females are believed to breed at one year while males are believed to defer breeding until their second year (Orians 1961; Payne 1969).