|Scientific Name:||Agelaius tricolor|
|Species Authority:||(Audubon, 1837)|
|Red List Category & Criteria:||Endangered A2bc+3bc+4bc ver 3.1|
|Reviewer(s):||Butchart, S. & Symes, A.|
|Contributor(s):||Bond, M., Butcher, G., Cook, L. & Cook, R.|
|Facilitator/Compiler(s):||Bird, J., Butchart, S., Derhé, M., Ekstrom, J., Fisher, S., Harding, M., Temple, H., Khwaja, N.|
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. A possible reduction in the rate of decline would lead to the species being downlisted to a lower threat category if confirmed.
|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, and estimated that the global population had declined by more than 50% since 1934 (DeHaven et al. 1975). Censuses conducted throughout 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, state-wide volunteer-based censuses conducted throughout California located 257,000 individuals attending 121 breeding colonies in 2005 (King et al. 2006), 394,858 in 180 sites in 32 counties in 2008 (Kelsey 2008) and 259,322 at 138 sites in 29 counties in 2011 (Kelsey 2011). These results suggest that recent declines may not have been as severe as previous estimates reported, but that steep declines (almost 35%) occurred between 2008 and 2011. These apparent declines may be due to discrepancies in survey methodology, but are likely to be partly caused by low reproductive success that has been documented in reports over the past three years (Meese 2008, 2009a, 2009b). 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 stable (G. Butcher in litt. 2006). 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.|
Native:Mexico; United States
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Rich et al (2003)|
|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, in upland habitats (especially thickets of non-native Himalayan blackberry Rubus discolor), and in silage fields (Jaramillo and Burke 1999, Cook and Toft 2005), with 50% of the birds in California during the 2008 statewide survey observed nesting in silage fields (Kelsey 2008). It forages in agricultural areas, particularly where livestock are present and grass is short, and shows a preference for roosting in marshes (Jaramillo and Burke 1999). 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 clams (Beedy and Hamilton 1999). Breeding typically occurs between April and 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 migratorius (Cook and Toft 2005). 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 habitat (Cook and Toft 2005). 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 nests (Cook and Toft 2005). 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 summer (Jaramillo and Burke 1999).|
|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 declines (Cook and Toft 2005). Additionally, 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 to be a significant threat in California (L. Cook in litt. 2012). Some birds are shot in the rice-growing regions of northern Central Valley (L. Cook in litt. 2012). Losses of formerly productive foraging habitats to perennial, woody crops (primarily almonds and grapes) and to urbanisation are also serious threats. 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 well (DeHaven et al. 1975).|
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 threatened (Cook and Toft 2005). A conservation action 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 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 lands (M. Bond in litt. 2005). Management guidelines have been produced (Beedy and Hamilton 1997, DeHaven 2000). In 2008, an agreement was reached between Audubon California and a local farmer to safeguard a single colony of c.80,000 birds by delaying the harvest of 65 ha of farmland in Tulare County, California where the colony is nesting (Anon. 2008).
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 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 use (DeHaven 2000). Delay harvesting or herbicide applications until after the colony completes the breeding cycle (Beedy and Hamilton 1999). Protect and enhance Toledo Pit (Tulare County), an important breeding site (DeHaven 2000). 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 success. Conduct studies of foraging ecology to determine key characteristics and possibilities to enhance foraging habitat. List the species as Endangered under federal law (M. Bond in litt. 2005).
|Citation:||BirdLife International 2012. Agelaius tricolor. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 17 December 2014.|
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