The tricolored blackbird has been the subject of intensive study for several decades due to observed declines and absences from portions of their range, and the conservation of the species has recently received increased attention due to the listing of the species under the California Endangered Species Act in December 2014. The Center for Biological Diversity filed a petition with the U.S. Fish and Wildlife Service to list the species as endangered under the U.S. Endangered Species Act on February 3rd, 2015. The Tricolored Blackbird Working Group produced a Conservation Plan in 2007 to guide conservation efforts and the Conservation Plan is being revised in 2015.
Decline in Abundance
The original, pre-Columbian abundance of the tricolored blackbird is unknown and likely unknowable. The tricolor was described as the most abundant bird species in coastal southern California, in the region from Santa Barbara through San Diego, at the end of the 19th Century (Cooper in Baird and Cooper 1859, Unitt 2004). The first intensive studies dedicated to estimating tricolored blackbird abundance began in the 1930's in response to criticism of the Bureau of Biological Survey (the forerunner of the U.S. Fish & Wildlife Service) for failure to respond to perceived widespread reductions in abundance prior to 1931 (Neff 1937). Neff conducted six years of field work across large portions of the species' range, from the northern Sacramento Valley to southern California, and his abundance estimates were derived from counts of nests during or following the breeding season. Neff (1937) and his assistants studied breeding tricolored blackbirds and found single colonies consisting of up to 282,000 nests, with a maximum number 491,000 nests from a sample of 8 colonies in 1934. Extrapolating from Neff's estimates, one may conservatively estimate the number of tricolored blackbirds as in the range of 2-3 million birds in the 1930's.
DeHaven and colleagues looked at the abundance of tricolors in the early 1970s and concluded that the species had declined by at least 50% in the 35 years since Neff's work. Subsequent field workers tried to estimate the statewide population of tricolors via a volunteer-based survey originally conceived and coordinated by Ted Beedy and Bill Hamilton. These so-called Tricolored Blackbird Statewide Surveys attempted to detect and estimate the sizes of all colonies across the entire state during a 3-day interval in late April, when the birds are most reliably counted. These statewide surveys began in 1994 and from 1994 to 2005 produced estimates of numbers of tricolors in the range of 250,000 birds (i.e. fewer birds than had been estimated from a single colony by Neff in the 1930's). There was much variation in the level of effort and in geographic completeness among the 1994-2005 Statewide Surveys, however, and trying to deduce a population trend by comparing the results of these surveys is difficult.
The 2008 triennial Statewide Survey, which differed from previous Statewide Surveys by having 1) county coordinators, 2) data management, and 3) data entry via this Tricolored Blackbird Portal, estimated the statewide population at approximately 400,000 birds, the 2011 Statewide Survey estimated that only 258,000 birds remained, and in 2014 the statewide population estimate was only 145,000 birds, which prompted the California Fish and Game Commission to list the species as Endangered under the California Endangered Species Act.
Reasons for the Decline
The reasons for the decline of tricolors are many, but include:
- habitat losses due to water diversions and draining of wetlands
- habitat losses due to conversion to agriculture
- habitat losses due to urbanization
- deliberate shooting for sale at markets ("market-hunting")
- deliberate shooting and poisoning as agricultural pests
Taken together, these factors have reduced the available breeding and foraging habitats by transforming the landscapes in which the birds evolved, and reduced the numbers of adults by shooting and poisoning during and following the breeding season. Although deliberate shooting and poisoning were prohibited in the 1970's and 1980's, habitat losses continue.
More recently, and continuing to the present, are three additional factors that affect productivity of tricolors:
- replacement of annual and perennial row crops (primarily alfalfa and sunflowers) and shrublands, which often support large insect populations and therefore provide excellent food sources, by woody perennial crops (vineyards and almond orchards), which are insect-poor and do not provide foraging opportunities; this process severely restricts essential foraging habitats surrounding potential nesting sites and may prevent the utilization of otherwise suitable nesting substrate;
- predation by large numbers (e.g., 125 or more in a single colony) of cattle egrets, a voracious predator that was unknown in tricolor colonies until first observed in 2006, but that has subsequently become a serious threat to large, potentially highly productive colonies in the southern San Joaquin Valley;
- harvest of the grain fields used as nesting substrate while eggs or young are still in the nests; this causes catastrophic failure of entire breeding efforts that often affect tens of thousands of birds.
The following video was filmed in Merced County in 2006 and shows the destruction of a Tricolored Blackbird colony during the harvest of a grain field.
Several conservation actions have been undertaken to stem the decline of the tricolored blackbird and to rebuild its numbers to sustain the species well into the future; these include:
- annual detection and monitoring of colonies in the Central Valley; this effort provides for the detection of the largest colonies in the San Joaquin and Sacramento Valleys and near-real-time monitoring of their fates
- conservation of the largest "silage colony" (i.e. nesting colony established in a triticale field in the San Joaquin Valley) through voluntary sale by the landowner and purchase by the state or federal government or non-governmental organization; a process known as a "silage buy-out"
- conservation of "silage colonies" by harvest delay; this procedure involves paying a willing landowner to delay the maturation of his triticale crop by adding an extra irrigation to his irrigation schedule, with the costs associated with the extra irrigation reimbursed to the landowner; this procedure is desirable because it allows the farmer to havest his crop while also allowing the birds to fledge their young and is quite inexpensive compared to the cost of a silage buy-out
- provision of attractive nesting substrate on National Wildlife Refuges and other protected areas; the provision of secure nesting substrate is an essential component of the long-term strategy to conserve the birds; birds nesting in the protected area then forage widely around the colony, on both protected land and private property
- assisting private property owners to provide nesting substrate; this program, with funding by the Landowner Incentive Program (http://wsfrprograms.fws.gov/Subpages/GrantPrograms/LIP/LIP.htm) of the U.S. Fish & Wildlife Service's Wildlife & Sport Fish Restoration Programs, provides funding to private property owners who agree to provide specific habitat conditions in exchange for grant support; this program has for several years been supporting landowers who wish to assist efforts to conserve tricolors. However, funding for the LIP program was not provided in the 2008 Department of the Interior budget, and unless funding is restored, financial support for on-the-ground conservation actions will not be available from this source.
- provision of "lure grains", typically rolled corn, on the periphery of colonies to provide grains for birds that would otherwise consume grains from nearby dairies[g2:194 class="right"]
- triennial statewide survey; every 3 years, a volunteer statewide survey is performed to comprehensively monitor tricolor distribution and abundance
- education and outreach; brochures have been produced and distributed which educate landowners and agency personnel to the status of the tricolor and to efforts being made to conserve it; in addition, good working relations have been established with many landowners who permit monitoring of colonies on their properties; presentations to local Audubon chapters and similar conservation organizations provide additional education and outreach opportunities
- banding; by early 2015 nearly 57,000 tricolors have been banded since 2007, documenting spatial and temporal patterns of movements and providing estimates of life history parameters
- web portal; this web portal provides current, documented information on tricolors and access to data and reports provided by tricolor researchers, as well as web-based data input capabilities to participants in the triennial Statewide Surveys