Agelaius tricolor

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

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Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	AVES	Passeriformes	Icteridae

Scientific Name:

Agelaius tricolor

Species Authority:

(Audubon, 1837)

Common Name/s:

English

–

Tricoloured Blackbird, Tricolored Blackbird

Assessment Information [top]

Red List Category & Criteria:

Endangered A2bc+3bc+4bc ver 3.1

Year Assessed:

2008

Assessor/s

BirdLife International

Evaluator/s:

Bird, J. & Butchart, S. (BirdLife International Red List Authority)

Justification:
This colonially breeding species is listed as Endangered because available information indicates that it is undergoing very rapid declines owing to loss of its upland nesting habitat, low reproductive success in native habitats and complete breeding failure in harvested agricultural fields.

History:

2006	–	Endangered
2004	–	Least Concern
2000	–	Lower Risk/least concern
1994	–	Lower Risk/least concern
1988	–	Lower Risk/least concern

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, USA. It has also been recorded in Oregon, west Nevada³, Washington², 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. The California population is thought to make up >95% of the global population¹. In 1934, systematic surveys estimated >700,000 adults in just eight Californian counties, and found breeding birds in 26 counties, including one colony containing >200,000 nests (about 300,000 adults) covering 24 ha⁴. Studies in 1969-1972 reported an average of about 133,000 individuals/yr in Central Valley, and estimated that the global population had declined by >50% since 1934⁵. Intensive censuses conducted throughout California in 1994, 1997 and 2000 gave figures of 370,000, 233,000 and 162,000 respectively^1,2. This equates to a decline of 56% in six years. Further censuses conducted throughout California in 2005 located 257,000 individuals attending 121 breeding colonies¹⁰, suggesting that recent declines have not been as severe as previous estimates reported, though conjecture remains over the comparability of these latest survey estimates with previous figures. The Christmas Bird Count has recorded the species regularly at 120 sites over a 39 year period, and that data suggests the population may be relatively stable¹¹. This species has proven very difficult to sample, as confirmed by the considerable variation in population estimates. To clarify its status, a thorough, unbiased and consistent approach to sampling is needed in the future.
Countries:	Native: Mexico; United States
Range Map:	(click map to view full version)

Population [top]

Population:	Rich et al (2003)
Population Trend:	Decreasing

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 Sierras². It breeds in freshwater marshes with tall emergent vegetation, in upland habitats (especially thickets of non-native Himalayan blackberry Rubus discolor), and in silage fields^1,3. It forages in agricultural areas, particularly where livestock are present and grass is short, and shows a preference for roosting in marshes³. An opportunistic forager, 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 clams². Breeding typically occurs in April-July, when individuals congregate to form massive breeding colonies that are larger than those of any other extant North American landbird following the extinction of the Passenger Pigeon Ectopistes migratorius¹. Reproductive success is significantly higher in non-native upland vegetation (primarily Himalayan blackberry) than it is in native wetland vegetation (cattail Typha spp. and bulrush Scirpus spp.), its predominant historic breeding habitat¹. In silage fields, which hold a significant proportion of the breeding population (17% in 2000), reproductive success can be disastrously low, as harvesting can result in the loss of entire colonies with tens of thousands of nests¹. Although it can be found throughout the breeding range during winter, the species is nevertheless partly migratory, with large numbers of birds being seen along the central Californian coast in the winter even though few nest in this area in the summer³.
Systems:	Terrestrial

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 Sierras². It breeds in freshwater marshes with tall emergent vegetation, in upland habitats (especially thickets of non-native Himalayan blackberry Rubus discolor), and in silage fields^1,3. It forages in agricultural areas, particularly where livestock are present and grass is short, and shows a preference for roosting in marshes³. An opportunistic forager, 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 clams². Breeding typically occurs in April-July, when individuals congregate to form massive breeding colonies that are larger than those of any other extant North American landbird following the extinction of the Passenger Pigeon Ectopistes migratorius¹. Reproductive success is significantly higher in non-native upland vegetation (primarily Himalayan blackberry) than it is in native wetland vegetation (cattail Typha spp. and bulrush Scirpus spp.), its predominant historic breeding habitat¹. In silage fields, which hold a significant proportion of the breeding population (17% in 2000), reproductive success can be disastrously low, as harvesting can result in the loss of entire colonies with tens of thousands of nests¹. Although it can be found throughout the breeding range during winter, the species is nevertheless partly migratory, with large numbers of birds being seen along the central Californian coast in the winter even though few nest in this area in the summer³.

Systems:

Terrestrial

Threats [top]

Major Threat(s):	Loss of upland nesting habitat, combined with low reproductive success in native habitats and complete breeding failure in harvested agricultural fields, are the most likely causes of recent declines¹. Additionally, herbicide spraying and contaminated water are suspected to have caused complete breeding failure in several colonies². Historic declines may have occured because of the loss of native wetlands (which have declined in area by >95% since the arrival of Europeans), loss of grasslands and grasshoppers (a main component of the species' diet), hunting, and large-scale poisoning efforts to control crop depredation that continued until the 1960s^1,4,5Because breeding success is so poor in native wetlands, protection of these habitats will not reverse population declines in the species - conservation measures must focus on agricultural land and upland habitats as well⁵.

Major Threat(s):

Loss of upland nesting habitat, combined with low reproductive success in native habitats and complete breeding failure in harvested agricultural fields, are the most likely causes of recent declines¹. Additionally, herbicide spraying and contaminated water are suspected to have caused complete breeding failure in several colonies². Historic declines may have occured because of the loss of native wetlands (which have declined in area by >95% since the arrival of Europeans), loss of grasslands and grasshoppers (a main component of the species' diet), hunting, and large-scale poisoning efforts to control crop depredation that continued until the 1960s^1,4,5Because breeding success is so poor in native wetlands, protection of these habitats will not reverse population declines in the species - conservation measures must focus on agricultural land and upland habitats as well⁵.

Conservation Actions [top]

Conservation Actions:	Conservation actions underway: It is currently 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 threatened¹. 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 survival of an estimated 37,000 to 44,000 first-year adults to the 1994 and 1995 breeding seasons² and benefited the population in 2003. However, the US Fish and Wildlife Service take the position that crop purchases or reimbursements for delayed harvest are not a feasible long-term solution for the species' management on private agricultural lands⁸. Management guidelines have been produced^6,7. Conservation actions proposed: Maintain a viable, self-sustaining population throughout current geographic range⁶. Avoid losses of colonies and their associated habitats and increase the breeding population on suitable public and private lands managed for this species⁶. Enhance public awareness and support for protection of habitat and active colonies⁶. Create low-risk nesting substrates such as marshes and blackberries within key dairy regions of the San Joaquin and Sacramento Valleys, to provide alternative nesting sites to grain silage fields, and monitor their use⁷. Delay harvesting or herbicide applications until after the colony completes the breeding cycle². Protect and enhance Toledo Pit (Tulare County), an important breeding site⁹. Conduct regular range-wide censuses to monitor population trends. Initiate mark-recapture and ratio-telemetry studies to determine demographic rates such as survival, reproduction, and population growth, and site fidelity as related to reproductive success⁸. Conduct studies of foraging ecology to determine key characteristics and possibilities to enhance foraging habitat⁸. List the species as Endangered under Federal law⁸.

Conservation Actions:

Conservation actions underway:

It is currently 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 threatened¹. 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 survival of an estimated 37,000 to 44,000 first-year adults to the 1994 and 1995 breeding seasons² and benefited the population in 2003. However, the US Fish and Wildlife Service take the position that crop purchases or reimbursements for delayed harvest are not a feasible long-term solution for the species' management on private agricultural lands⁸. Management guidelines have been produced^6,7.

Conservation actions proposed:

Maintain a viable, self-sustaining population throughout current geographic range⁶. Avoid losses of colonies and their associated habitats and increase the breeding population on suitable public and private lands managed for this species⁶. Enhance public awareness and support for protection of habitat and active colonies⁶. Create low-risk nesting substrates such as marshes and blackberries within key dairy regions of the San Joaquin and Sacramento Valleys, to provide alternative nesting sites to grain silage fields, and monitor their use⁷. Delay harvesting or herbicide applications until after the colony completes the breeding cycle². Protect and enhance Toledo Pit (Tulare County), an important breeding site⁹. Conduct regular range-wide censuses to monitor population trends. Initiate mark-recapture and ratio-telemetry studies to determine demographic rates such as survival, reproduction, and population growth, and site fidelity as related to reproductive success⁸. Conduct studies of foraging ecology to determine key characteristics and possibilities to enhance foraging habitat⁸. List the species as Endangered under Federal law⁸.

Citation:	BirdLife International 2008. Agelaius tricolor. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on 09 February 2010.
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