Data Zone
Justification of Red List category
This colonially breeding species is listed as Endangered because it has undergone rapid declines in excess of 60% in recent years, largely in response to losses of nesting and foraging habitat, low reproductive success in native habitats correlated with low insect abundance, persistent insecticide use and until recently, breeding failure in harvested agricultural fields. Despite comprehensive monitoring, a rapid increase in knowledge and citizen science-aided surveys, and effective data management, only in the past five years has there been considerable efforts and a legal framework to prevent the destruction of breeding colonies. Declines may have slowed or reversed in recent years however, the most recent population survey is yet to occur and as such, given the extremely rapid declines evidenced in recent years, the species is retained as Endangered. Further evidence that suggests declines have slowed/reversed may result in this species being listed under a lower threat category.
Population justification
The global population size has been estimated at 175,000 individuals (Meese 2017), up slightly from the estimate of 145,000 individuals in 2014 (Meese 2014), indicating that the global population is considerably below 200,000 individuals.
Trend justification
Agelaius tricolor has undergone extremely rapid population declines in the past. Declines were thought to reach a maximum between 2008-2014 where statewide surveys in California (which comprises over 95% of the global population) revealed a 63% decline, equivalent to an ~86% decline across three generation lengths (12 years) (Meese 2015). However, tentative population increases have been suggested in the years since, particularly between 2014-2017 (Meese 2017, R. Meese in litt. 2020, Meehan et al. 2018) and as such, it is thought that such rapid declines may be historic. A new statewide population survey scheduled for early 2020 was postponed and as such, the population trend is retained here within the band 50-79% to reflect the recent, rapid declines but also possible recovery in the past few years.
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, from one site in western Nevada (Ammon and Woods 2008), Washington (Beedy and Hamilton 1999), and extreme northwest Baja California (Mexico). It has a limited range, 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 supported by data entry and management provided by the Tricolored Blackbird Portal (http://tricolor.ice.ucdavis.edu) has been undertaken triennially from 2008 (Meese 2014, 2015). 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 and 884 locations in 44 counties in 2017 (Meese 2014, 2017). The number of breeding sites surveyed increased in each survey, with a total of 802 in 2014 (Meese 2014). These results suggest that recent declines have been in excess of 60%, even if there had been a period of less rapid declines prior to this. Meehan et al. (2019) also report a ~40% decline in A. tricolor average colony size between 2008-2017 whilst Robinson et al. (2018) report a mean decline of 34% in Californian tricolored blackbird populations between 2007-2016 based on citizen science data. 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).
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); the wintering population on the outer Point Reyes Peninsula (Marin County) was once estimated to annually comprise 15-20,000 birds but fewer than 1,000 have been seen each year since 2014 whilst a site in Solano County, comprised an estimated 50,000 birds in October 2007 but has numbered only 4,000 or fewer since 2017 (R. Meese in litt. 2016).
The most dominant causes of recent declines have been the 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, although the latter has virtually ceased in the past 5 years due to new agricultural incentives (Cook and Toft 2005, R. Meese in litt. 2020). Losses of formerly productive foraging habitats to perennial, woody crops (primarily walnuts, almonds, pistachios and grapes) and to urbanisation are currently the most serious threats to the species's survival (R. Meese in litt. 2020). Invertebrate availability close to nesting sites during the breeding season also appears to be a major factor driving declines, and widespread application of persistent neonicotinoid insecticides may have diminished invertebrate populations close to nesting sites (Beedy and Hamilton 1997, Meese 2014, cf. Benton et al. 2002); conservation measures must focus on surrounding agricultural land and upland habitats to provide invertebrates needed for successful breeding (Meese 2013). 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). All blackbird species, including the Tricolored, could be legally shot up until the 1980s if causing, or about to cause, depredations in fields of ripening rice in Autumn in Sacramento Valley. Whilst the Tricolored Blackbird can no longer be targeted, other blackbird species may still be legally shot in fields of ripening rice and Tricolored Blackbird may be accidentally killed if mistaken for the essentially similar red-wing, which is primarily responsible for rice depredation (DeHaven 1971); there is currently no quantification of this threat (R. Meese in litt. 2020). Predation by non-native Cattle Egret Bubulcus ibis and predation on eggs by the native White-faced Ibis (Plegadis chihi) have also been a significant threat to particular colonies in Tulare County (Meese 2012, R. Meese in litt. 2016).
Conservation Actions Underway
The U.S. Fish and Wildlife Service declined to list the species under the Endangered Species Act (ESA) in August 2019 but the California Department of Fish and Wildlife listed the species as Threatened under the California Endangered Species Act (CESA) in April 2019. 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. Breeding colonies are now fully protected under CESA and all harvest of grain field colonies should cease. No breeding colonies were known to have been lost due to harvest of their grain field nesting substrates in 2018 nor 2019. 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's 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), ending in 2019. An extensive state-wide census using uniform methods supported by data entry and management provided by the Tricolored Blackbird Portal (http://tricolor.ice.ucdavis.edu) has been undertaken triennially from 2008 (Meese 2014, 2015) and since 2015, an additional sampling survey has been undertaken (Meese et al. 2015) although funding constraints prevented the survey occurring annually as was hoped..
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.
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.
Text account compilers
Martin, R., Everest, J.
Contributors
Bird, J., Bond, M., Butchart, S., Butcher, G., Cook, L., Cook, R., Derhé, M., Ekstrom, J., Fisher, S., Harding, M., Holyoak, M., Khwaja, N., Meese, R.J. & Temple, H.
Recommended citation
BirdLife International (2024) Species factsheet: Tricolored Blackbird Agelaius tricolor. Downloaded from
https://datazone.birdlife.org/species/factsheet/tricolored-blackbird-agelaius-tricolor on 25/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 25/12/2024.