The tricolored blackbird has been the subject of intensive study for several decades due to observed absences from previous portions of their range, and the conservation of the species has recently received increased attention due to the petition to list the species under the protections of the federal and state of California Endangered Species Acts. Although these petitions were declined, the tricolor remains a species of concern and the focus of conservation efforts. The Tricolored Blackbird Working Group has recently produced the Conservation Strategy, a guide to conservation efforts and a response to concerns over documented declines in the distribution and abundance of the species. These declines have occurred primarily in the 20th Century in apparent response to widespread, landscape-level changes in regions where they were formerly abundant.
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 of nests from a sample of 8 colonies of 491,000 nests 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.
Subsequent efforts to estimate the global population of tricolors consisted of volunteer-based surveys suggested and coordinated by Ted Beedy and Bill Hamilton. These 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 the 1990's and 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), until a population low was estimated in 2000, when only 150,000 birds were counted (Hamilton 2000). The abundance of tricolors increased subsequent to the 2000 survey, due primarily, it is believed, to the annual conservation of a few, large, highly-productive early-season colonies in the San Joaquin Valley, and in 2005, a minimum population of 260,000 birds was estimated (Hamilton and Meese 2005). The 2008 triennial Statewide Survey estimated that approximately 400,000 birds exist in California, and suggest that the apparent increase in abundance in the Central Valley is continuing. However, only approximately 5,500 tricolors were observed in southern California during the 2008 Survey, and this population segment appears to be in great jeopardy of extinction.
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
- color-banding; the color-banding of nearly 1,800 adult tricolors in 2007 will help scientists to better understand the spatial and temporal movements of tricolors; reports of observations of color-banded tricolors have been solicited from the many hundreds of birders in California
- web portal; this web portal provides current, documented information on tricolors and access to data and reports provided by tricolor researchers, as well as data input capabilities to those participating in the triennial survey