Agelaius tricolor 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Passeriformes Icteridae

Scientific Name: Agelaius tricolor (Audubon, 1837)
Common Name(s):
English Tricolored Blackbird, Tricoloured Blackbird
Taxonomic Source(s): del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A., Fishpool, L.D.C., Boesman, P. and Kirwan, G.M. 2016. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2: Passerines. Lynx Edicions and BirdLife International, Barcelona, Spain and Cambridge, UK.
Identification information: 18-24cm. A slim, sexually dimorphic New World blackbird. Male is entirely black with dull blue gloss, except for striking epaulets made up of deep red lesser coverts and white median coverts. Female is largely dark blackish-brown with a paler throat and streaked underparts. Juvenile is similar to adult female, but duller and buffier. Similar spp. Identification of this species is difficult owing to its similarity to Red-winged Blackbird A. phoenicius, and to the variability of that species. Males of A. tricolor differ from A. phoenicius in having deeper red epaulets with purer white borders,  whereas females have darker brown and less extensively streaked plumage. Both males and females are slimmer-billed and show more square-tipped tails than A. phoenicius. The breeding behaviour of the two species is very different. Voice Male song is a nasal, drawn-out guuuaaaak lasting 1-1.5 seconds. Alarm and flight calls are a nasal chwuk and churr respectively. A range of other short, nasal call notes are heard.

Assessment Information [top]

Red List Category & Criteria: Endangered A2bc+3bc+4bc ver 3.1
Year Published: 2017
Date Assessed: 2016-10-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Bond, M., Butcher, G., Cook, L., Cook, R., Meese, R.J. & Holyoak, M.
Facilitator/Compiler(s): Bird, J., Butchart, S., Derhé, M., Ekstrom, J., Fisher, S., Harding, M., Temple, H., Khwaja, N., Martin, R
This colonially breeding species is listed as Endangered because there is an ongoing, directly estimated very rapid population decline in excess of 60% due to losses of nesting and foraging habitat, impacts of drought, low reproductive success in native habitats correlated with low insect abundance and complete breeding failure in harvested agricultural fields. Despite comprehensive monitoring, and considerable efforts to prevent destruction of colonies, rates of decline remain alarmingly rapid.

Previously published Red List assessments:

Geographic Range [top]

Range Description:Agelaius tricolor is near-endemic to California, breeding mainly in the Central Valley and other points west of the Cascades and Sierra Nevada, U.S.A. It has also been recorded in Oregon, west Nevada (Jaramillo and Burke 1999), Washington (Beedy and Hamilton 1999), and extreme northwest Baja California (Mexico). It has a large range, with an estimated global Extent of Occurrence of 113,000 km2, which has not contracted since the 1930s. Californian birds are thought to make up over 95% of the global population (Cook and Toft 2005). In 1934, systematic surveys estimated over 700,000 adults in just 8 Californian counties, and found breeding birds in 26 counties, including one colony containing over 200,000 nests (c.300,000 adults) covering 24 ha (Neff 1937). Studies in 1969-1972 reported an average of about 133,000 individuals/year in Central Valley (DeHaven et al. 1975). Trend identification in the species has been hampered by the itinerant nature of colonies formed in agricultural, hence ephemeral, habitats (Hamilton III 1998), which now represent the largest proportion of the breeding population (Graves et al. 2013). What is clear is there was a decline exceeding 63% between the 1930s and 1980s (Beedy et al. 1991, Graves et al. 2013), and further declines have occurred since (Cook and Toft 2005, Meese 2014). Censuses conducted in California in 1994, 1997 and 2000 gave figures of 370,000, 233,000 and 162,000 individuals respectively (Beedy and Hamilton 1999, Cook and Toft 2005), equating to a decline of 56% in six years. However, a volunteer-based census in California in 2005 located 257,000 individuals attending 121 breeding colonies (King et al. 2006). A more extensive state-wide census using uniform methods has been undertaken triennially from 2008 (Meese 2014). In 2008, 394,858 individuals were recorded at 180 sites in 32 counties (Kelsey 2008), 259,322 at 138 sites in 29 counties in 2011 (Kelsey 2011) and 145,135 at 143 sites in  37 counties in 2014 (Meese 2014). The number of visited sites increased in each survey, with a total of 802 in 2014 (Meese 2014). These results suggest that current declines are once more in excess of 60%, even if there had been a period of less rapid declines prior to this. The Christmas Bird Count has recorded the species regularly at 120 sites over a 39 year period (G. Butcher in litt. 2006), but numbers are so low compared to the size of breeding colonies that any population level inference from this data is difficult (M. Holyoak in litt. 2016). Indeed, it is reported that non-breeding gatherings along the central Californian coast have ceased within the last decade (R. Meese in litt. 2016).

Countries occurrence:
Mexico; United States
Additional data:
Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:188000
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:11-100Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:No
Upper elevation limit (metres):1300
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The global population size has been estimated at 300,000 individuals (Rosenberg et al. 2016), although the California-wide survey in 2014 (considered to hold 95% of the global population) directly estimated a breeding population of 145,000 individuals (Meese 2014), indicating that the global population is below 200,000 individuals.

Trend Justification:  A very rapid and on-going population decline in excess of 60% has been estimated directly, based on repeated censuses (using the same methods) of the Californian population (which comprises the majority of the global population).
Current Population Trend:Decreasing
Additional data:
Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:2-100Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:It is a lowland species, but has bred to 1,300 m in the Klamath area (Oregon) and along the west side of the Sierras (Beedy and Hamilton 1999). It breeds in freshwater marshes with tall emergent vegetation, as well as in stinging nettle Urtica dioica, in a wide variety of upland habitats (especially thickets of non-native Himalayan blackberry Rubus discolor and milk thistle Silybum marianum), and in grain fields (especially wheat x rye 'triticale') grown as silage (Jaramillo and Burke 1999, Cook and Toft 2005). 50% of the birds in California during the 2008 statewide survey nested in triticale silage fields (Kelsey 2008). It forages mainly in open rangelands, shrublands and in some agricultural areas, particularly where livestock are present, and shows a preference for roosting in marshes (Jaramillo and Burke 1999). An opportunistic forager, during the breeding season the species takes any locally abundant insect including grasshoppers (Orthoptera), beetles and weevils (Coleoptera), caddis fly larvae (Trichoptera), moth and butterfly larvae (Lepidoptera), dragonfly larvae (Odonata), and lakeshore midges (Diptera), as well as grains, snails, and small clams (Beedy and Hamilton 1999). Breeding typically occurs between March and July, when individuals congregate to form (at least formerly) massive breeding colonies that are larger than those of any other extant North American landbird following the extinction of the Passenger Pigeon Ectopistes migratorius (Cook and Toft 2005). Recent reproductive success is significantly higher in non-native upland vegetation (primarily Himalayan blackberry) than it typically is in native wetland vegetation (cattail Typha spp. and bulrush Scirpus spp.), its predominant historic breeding habitat (Cook and Toft 2005, Meese 2008, 2009a,b). Low reproductive success is correlated with low invertebrate abundance (Meese 2013). In silage fields reproductive success can be disastrously low as harvesting can result in the loss of entire colonies with tens of thousands of nests (Cook and Toft 2005). Although it can be found throughout the breeding range during winter, the species is partly migratory, with large numbers of birds formerly being seen along the central Californian coast in the winter even though few nest in this area (Jaramillo and Burke 1999). These gatherings have seemingly ceased to occur in the space of the last decade and very few are now observed along the coast in winter (R. Meese in litt. 2016).

Systems:Terrestrial; Freshwater
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):5.9
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s): Loss of upland foraging habitat to agriculture and urbanisation, combined with low reproductive success in native habitats and complete breeding failure in harvested agricultural fields, are the most likely causes of recent declines (Cook and Toft 2005). Invertebrate availability close to nesting sites during the breeding season appears to be a major factor driving declines, and widespread application of persistent insecticides may have diminished invertebrate populations close to nesting sites (Beedy and Hamilton 1997, Meese 2014, cf. Benton et al. 2002). The period of the most recent very rapid declines has coincided with significant drought throughout the state (Meese 2013, 2014, M. Holyoak in litt. 2016), which could also be expected to have reduced insect availability considerably. Separately, herbicide spraying and contaminated water are suspected to have caused complete breeding failure in several colonies (Beedy and Hamilton 1999). Historic declines may have occurred because of the loss of native wetlands (which have declined in area by over 95% since the arrival of Europeans), loss of grasslands and grasshoppers (a main component of the species's diet), hunting, and large-scale poisoning efforts to control crop depredation that continued until the 1960s (Neff 1937, DeHaven et al. 1975, Cook and Toft 2005).
Predation by non-native Cattle Egret Bubulcus ibis appears and predation on eggs by the native White-faced Ibis (Plegadis chihi) have been a significant threat to particular colonies in Tulare County (Meese 2012, Meese in. litt. 2016). Some birds are shot in mixed-species flocks in autumn in the rice-growing regions of northern Central Valley (L. Cook in litt. 2012), though there is no quantification of this threat. Losses of formerly productive foraging habitats to perennial, woody crops (primarily almonds, pistachios and grapes) and to urbanisation are also serious threats. Conservation measures must focus on surrounding agricultural land and upland habitats to provide invertebrates needed for successful breeding (Meese 2013).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
Tricolored Blackbird is currently under formal review by the U.S Fish and Wildlife Service for listing under the Endangered Species Act (ESA), and by the California Department of Fish and Wildlife for listing under the California Endangered Species Act (CESA), hence is afforded protection under these provisions for the 12-month review period (from June 2016) (R. Meese in litt. 2016).
Previously it has been classified in California as a Species of Special Concern and a Migratory Bird of Management Concern, categories which identify reduced populations but do not include the legal protections offered to species listed as threatened (Cook and Toft 2005). A Conservation Plan for the species was published in 2007 (Tricolored Blackbird Working Group 2007). Measures have been taken at times to protect nesting colonies of the species, including purchasing portions of crops, or delaying harvest to avoid impacting nests during the active breeding season. These actions and participation by landowners resulted in the recruitment of an estimated 37,000 to 44,000 first-year adults to the 1994 and 1995 breeding seasons (Beedy and Hamilton 1999) and benefited the population in 2003. However, the U.S. Fish and Wildlife Service took the position that crop purchases or reimbursements for delayed harvest are not a feasible long-term solution for the species' management on private agricultural lands (M. Bond in litt. 2005). Management guidelines have been produced (Beedy and Hamilton 1997, DeHaven 2000, Meese and Beedy 2015). In 2015, a voluntary 5-year program was established to compensate dairy operators for delaying the harvest of their occupied grain fields until after the young had fledged in order to reduce losses due to agricultural operations (R. Meese in litt. 2016).
From 2015, in addition to the triennial state-wide survey, an annual sampling survey has been undertaken (Meese et al. 2015).

Conservation Actions Proposed
Maintain a viable, self-sustaining population throughout current geographic range. Avoid losses of colonies and their associated habitats and increase the breeding population on suitable public and private lands managed for this species. Enhance public awareness and support for protection of habitat and active colonies (Beedy and Hamilton 1997). Create secure nesting substrates within key dairy regions of the San Joaquin valley, to provide alternative nesting sites to grain silage fields, and monitor their use (DeHaven 2000, Meese and Beedy 2015). Delay harvesting or herbicide applications until after the colony completes the breeding cycle (Beedy and Hamilton 1999). Continue the triennial range-wide censuses to monitor the population and annual sampling survey to monitor trends in core areas. Continue mark-recapture and ratio-telemetry studies to determine demographic rates such as survival, reproduction, and population growth, and site fidelity as related to reproductive success. Conduct studies of foraging ecology to elucidate determinants of reproductive success and identify possibilities to enhance foraging habitat. List the species as Endangered under state and federal law (M. Bond in litt. 2005), and remove the exemption on autumn shooting of blackbirds in California for rice crop protection.

Amended [top]

Amended reason: Added new population estimates, information to the distribution and population, ecology,  threats and conservation actions text fields, with updated references.

Citation: BirdLife International. 2017. Agelaius tricolor (amended version of 2016 assessment). The IUCN Red List of Threatened Species 2017: e.T22724196A110603849. . Downloaded on 22 July 2018.
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