|
|
Agelaius tricolor
– Endangered
Taxonomy
|
Kingdom:
|
ANIMALIA
|
|
Phylum:
|
CHORDATA
|
|
Class:
|
AVES
|
|
Order:
|
PASSERIFORMES
|
|
Family:
|
ICTERIDAE
|
|
Scientific Name:
|
Agelaius tricolor
|
|
Species Authority:
|
(Audubon, 1837)
|
|
Common Name/s:
|
| English | — | TRICOLOURED BLACKBIRD |
|
Assessment Information
|
Red List Category & Criteria:
|
EN A2bc+3bc ver 3.1 (2001)
|
|
Year Assessed:
|
2006
|
|
Assessor/s:
|
BirdLife International
|
|
Evaluator/s:
|
Butchart, S. & Temple, H. (BirdLife International Red List Authority)
|
|
Justification:
|
This colonially-breeding species has been uplisted to Endangered because new 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:
|
| 1988 | - | Lower Risk/least concern (BirdLife International 2004) |
| 1994 | - | Lower Risk/least concern (BirdLife International 2004) |
| 2000 | - | Lower Risk/least concern (BirdLife International 2000) |
|
Geographic Range
|
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. The overall range of species is little changed since the mid-1930s, although numbers have declined markedly. 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 respectively1,2. This equates to a decline of 56% in six years. The California population is thought to make up >95% of the global population1, and thus the entire global population is now smaller than the size of individual colonies recorded in the 1930s.
|
|
Range Map:
|
 (click for detailed map)
|
|
Countries:
|
Native:
Mexico; United States
|
Population
|
Population Trend:
|
|
Habitat and Ecology
|
System:
|
Terrestrial; Freshwater
|
Threats
|
Threats:
|
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 1960s1,4,5 Because 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
|
Conservation Actions:
|
Conservation measures 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 the nesting activities of the species, including purchasing portions of crops to preserve some large colonies, 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. 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 produced6,7.
Conservation measures 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.
|
|
|
