Aves (Birds): Passeriformes, Icteridae
Tricolor blackbird (Agelaius tricolor)
Potential Occurrence: Nesting “Unlikely to Occur”
Status: (Nesting Colony)
Federal: None
State: Species of Special Concern
Other: MBTA G2G3 S2 BLM:S USFWS:BBC
Species Description:
Photo: Sparks 2009
The adult male of the Tricolor is entirely black, glossed
bluish (in full sunlight), with brownish-red feathers forming a reddish patch on wing shoulders
(epaulets) and buffywhite to pure-white feathers providing a lower border to the red (Mailliard
1910; Beedy and Hamilton 1999, citing DeHaven 1975 - not examined). The adult female “is
mostly black, with distinct grayish streaks; relatively whitish chin and throat, rarely with faint
pinkish or peach wash; and small but distinct reddish shoulder patch” (Beedy and Hamilton 1999,
citing DeHaven 1975 - not examined). (From Gustafson and Steele 2004)
Distribution:
Mostly a resident in California. Common locally throughout Central Valley and in coastal districts
from Sonoma Co. south. Breeds near fresh water, preferably in emergent wetland with tall, dense
cattails or tules, but also in thickets of willow, blackberry, wild rose, tall herbs. Feeds in grassland
and cropland habitats. Breeds locally in northeastern California. In winter, becomes more
widespread along central coast and San Francisco Bay area (Grinnell and Miller 1944, McCaskie
et al. 1979, Garrett and Dunn 1981) and is found in portions of the Colorado Desert. (From
Granholm 2008)
Life History & Threats:
The Tricolor is the most colonial passerine bird in North America forming large colonies that may
include thousands of birds at a single breeding site. Colonies usually nest near water in emergent
tule or cattail marsh, in armored vegetation like Himalayan blackberry, or in agricultural settings.
Colonies select sites near suitable foraging habitat. (From Gustafson and Steele 2004)
In California studies summarized by Skorupa et al. (1980), animal matter, mostly insects and
spiders, made up 86-91% of nestling and fledgling diet, and 28-96% of adult diet in spring and
summer. Seeds and cultivated grains, such as rice and oats, are other major foods, composing
most of fall and winter diet. Forages on ground in croplands, grassy fields, flooded land, and
along edges of ponds. (From Granholm 2008)
[The tricolor's] breeding season [lasts from] mid-April into late July. Polygynous; each male may
have several mates nesting in his small territory. A colony varies in size from a minimum of about
50 nests (Grinnell and Miller 1944) to over 20,000 in an area of 4 ha (10 ac), or less (DeHaven et
al. 1975). Colonies were even larger in former decades. Apparently has highest nesting density of
any blackbird in North America (Ehrlich et al. 1988). Clutch size usually 3 or 4 eggs, range 2-6;
may raise 2 broods per yr (Terres 1980). Incubation lasts about 11 days; altricial young tended by
female or by both parents. Young leave nest at about 13 days. Probably breeds first at 1 yr
(Harrison 1978). (From Granholm 2008)
The greatest threats to this species are the direct loss and degradation of habitat from human
activities (Beedy and Hamilton 1999). Entire colonies (up to tens of thousands of nests) in cereal
crops and silage are often destroyed by harvesting and plowing of agricultural lands (Beedy and
Hamilton 1999, Hamilton 2004, Cook and Toft 2005, Messe 2006). Concentration of a high
proportion of the known population in a few breeding colonies increases the risk of major
reproductive failures, especially in vulnerable habitats such as active agricultural fields. (From
Shuford and Gardali 2008)
Habitat & Habitat Associations:
Foraging Habitat:
Tricolor foraging habitats in all seasons include pastures, dry seasonal pools, agricultural fields
(such as large tracts of alfalfa with continuous mowing schedules), rice fields, feedlots, and
dairies. Tricolors also forage occasionally in riparian scrub, saltbush (Atriplex spp.) scrub, marsh
borders, and grassland habitats. Weed free row crops and intensively managed orchards and
vineyards do not serve as regular foraging sites. (From Beedy and Hamilton 1997)
Most tricolors forage within 5 km of their colony sites (Orians 1961b), but commute distances of
up to 13 km have been reported (Hamilton pers. obs.). Short distance foraging (i.e., within sight of
the colony) for nestling provisioning also is common. Both sexes provision nestlings. (From
Beedy and Hamilton 1997)
Nesting Habitat:
Tricolors have three basic requirements for selecting their breeding colony sites: (1) open
accessible water; (2) a protected nesting substrate, which is usually either flooded or thorny or
spiny vegetation; and (3) a suitable foraging space providing adequate insect prey within a few
kilometers (km) of the nesting colony (Beedy 1989, Hamilton et al. 1995). Almost 93 % of the 252
tricolor breeding colonies reported by Neff (1937) were in freshwater marshes dominated by tules
(Scirpus sp.) and cattails (Typha sp.). The remaining colonies in Neff’s study were in willows
(Salix spp.), blackberries (Rubus sp.), thistles (Cirsium and Centaurea spp.), or nettles (Urtica
sp.). An increasing percentage of tricolor colonies in the 1980s and 1990s were reported in
Himalaya berries (Rubus discolor), and some of the largest recent colonies are in silage and grain
fields (Hamilton et al. 1995). (From Beedy and Hamilton 1997)
Conceptual Basis for GIS Model Development: To identify potential habitat for Tricolored
Blackbird in the Study Area, we mapped:
Foraging Habitat:

Pastures (mapped as grasslands)

Agricultural fields

Seasonal ponds

Riparian scrub. Note that riparian vegetation was mapped as a 130-m buffer along the
main stem of Rancheria Creek. Riparian woodland, forest and scrub is disjunct within
this area.
Nesting Habitat:

Perennial ponds. Perennial ponds are the only sites with cattails and tules in the Study
Area.

Riparian vegetation. Note that riparian vegetation was mapped as a 130-m buffer along
the main stem of Rancheria Creek. Riparian woodland, forest and scrub vegetation is
disjunct within this area.
Potential Occurrence in the Galbreath Wildlands Preserve: Protection status for this species
applies to nesting colonies.
Habitat: Tricolored blackbird colonies nest near open accessible water on spiny or flooded
nesting substrates within a few kilometers of suitable foraging areas. Nesting habitat for this
species in the Preserve is poor or unavailable (Figure 87). Perennial water in the Preserve
occurs only in shaded tributaries that drain into Rancheria Creek and small ponds. Patches of
tules and cattails, the most common nesting substrate for this species, are too small to support
a colony. Willows, blackberries, thistles, or nettles occur in riparian areas along Rancheria
Creek. However, the GIS map overestimates riparian vegetation abundance, which is only
patchily distributed within the area identified. Surface water in the Creek is only available during
the winter and draws down occurs early in the spring and is not be available to nesting birds.
Nearest Occurrence:
Documented Occurrences in the Galbreath Wildlands Preserve: This species has not
been documented on the Preserve. To our knowledge no surveys have been conducted.
Nearest Occurrence to the Galbreath Wildlands Preserve: This species has been
reported to occur in the Hopland USGS quad to the east of the Preserve.
Summary: Nesting Tricolored Blackbirds are “Unlikely to Occur” in the Preserve due to the lack
of appropriate nesting habitat.
References
Beedy, E.C. and W.J. Hamilton III. 1997 September. Tricolored Blackbird Status Update and
Management Guidelines. Migratory Birds and Habitat Programs, U.S. Fish & Wildlife Service.
Bird and Mammal Conservation Program, California Department of Fish & Game.
<http://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=2920>. 2010 September 25.
Granholm, S. 2008 August. Tricolored Blackbird. California Wildlife Habitat Relationships
System. <http://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=2181>. 2010 September 25.
Gustafson, J. R., and D. T. Steele. 2004 Sepember 15. Evaluation of petition from Center for
Biological Diversity to list Tricolored Blackbird (Agelaius tricolor) as endangered. California
Department of Fish & Game, Habitat Conservation Planning Branch. <http://nrm.dfg.ca.gov/
FileHandler.ashx?DocumentID=7097>. 2010 September 25.
Shuford, W. D. and Gardali, T. editors. 2008. California Bird Species of Special Concern: A
ranked assessment of species, subspecies, and distinct populations of birds of immediate
conservation concern in California. Studies of Western Birds 1. Western Field Ornithologists,
Camarillo, California, and California Department of Fish and Game, Sacramento.
<http://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=10506>. 2010 September 25.
Sparks, L.A. 2009 June. Monitoring of the Tricolored Blackbird, Agelaius tricolor, within and
around Department of Fish & Game Lands in Western Merced County, 2008. California
Department of Fish & Game, Resource Assessment Program. <http://nrm.dfg.ca.gov/
FileHandler.ashx?DocumentID=17716>. 2010 September 25.
Species Account Description: Neal Ramus & Emily Harvey