Research and Monitoring
History of Research
Although the tricolored blackbird is mentioned in several articles and books dating to the mid-19th Century, the first field work focussed on tricolored blackbirds was that conducted by Johnson Neff. Johnson Neff was a biologist who worked for the Bureau of Biological Survey, the forerunner of today's U.S. Fish & Wildlife Service. Neff conducted six years of field surveys (from 1931-1936), and additional banding of nestlings until 1940, to determine the status of the birds in the Central Valley after widespread reports of the birds' disappearance from coastal locations and a sense of concern for the future of the species. Neff's work was primarily focused on the Sacramento Valley, but he also worked, in conjunction with other state and federal biologists and volunteers, at sites in the San Joaquin Valley and in southern California.
After 1940, perhaps in response to Neff's finding of fairly large numbers of remaining birds (e.g., 282,000 nests at one site in Glenn County in 1934), there followed a 20+ year period of relatively little research into tricolored blackbird status and biology.
In the 1960's, two then-graduate students from U.C. Berkeley, Gordon Orians and Robert Payne, conducted seminal research on blackbirds, including tricolors, that focused on behavior and adaptations for marsh nesting (Orians) and reproductive physiology (Payne) and helped to provide an ecological and evolutionary context for tricolor breeding, food preferences, and habitat selection and compared and contrasted tricolors with other blackbird species.
In the late 1960's, Frederick Crase, a Bureau of Reclamation biologist, and Richard DeHaven, who worked for the U.S. Fish & Wildlife Service, began working on the tricolored blackbird and studied food habits, habitat relationships, population status, and movement patterns. This work was described in a number of publications from the mid-1970's until the late 1980's (see Bibliography). This work confirmed the continuing decline in the number of tricolored blackbirds and highlighted the dependence of food supplies, especially insect abundance, on colony productivity, and suggested that otherwise apparently suitable nesting sites might be abandoned if surrounding foraging habitats were not sufficiently productive or extensive.
In the 1980's Edward C. (Ted) Beedy began field investigations of tricolors with an emphasis on both the estimation of the abundance of the species and on the factors responsible for the observed nesting failures of colonies in the Central Valley. Shortly thereafter, William J. (Bill) Hamilton III began his field investigations. Bill Hamilton's work was to continue uninterrupted for 13 field seasons, through 2005, and covered a wide range of topics, including population estimation (Beedy and Hamilton suggested using volunteers to conduct a statewide survey in a 3-day interval in April to best estimate the global population of the species), productivity estimation, foraging ecology, and the phenomenon known as "itinerant breeding", whereby individuals breed once in one location and then fly northward to a different location to breed again. Beedy and Hamilton wrote the Birds of North America treatment of the tricolored blackbird (Beedy and Hamilton 1999).
Efforts to conserve tricolored blackbirds include:
- annual field work to detect, monitor, and document the fates of the largest colonies to help to prioritize colonies for conservation actions, to estimate the numbers of breeding adults, to estimate the numbers of young produced (i.e. derive an estimate of colony productivity), and to identify the factors responsible for observed patterns of productivity
- annual banding of primarily adults birds at several breeding colonies to help to document spatial and temporal movements, estimate life history parameters, and to evaluate patterns of site fidelity
- education and outreach, including the production and distribution of brochures for landowners, dairymen, and rice farmers to provide information on the biology and status of tricolored blackbirds and describe conservation efforts
- development of this web portal to provide information on the tricolored blackbird and to accumulate, standardize, and disseminate data on colony locations and observations of both breeding and non-breeding birds
- triennial statewide survey to monitor the trend in the statewide population
- sample survey of a statistical sample of locations to obtain a statewide population estimate in non-statewide survey years
A major component of efforts to monitor trends in the distribution and abundance of tricolors is the Triennial Tricolored Blackbird Statewide Survey. The statewide survey was pioneered by Ted Beedy and Bill Hamilton in the 1980’s as a means to obtain an estimate of the number of tricolors throughout California. The statewide survey, which typically occurs over 3 days in mid-April, is a volunteer effort with participants from all over lower elevation regions of California and is directed by a statewide coordinator and implemented by county coordinators who are local experts that assemble the teams that conduct the survey.
The statewide survey occurs every 3 years and documents both presence and absence, along with an estimate of the number of tricolors and characteristics of occupied sites. The statewide survey provides current, reliable information on the numbers and distribution of tricolored blackbirds throughout California and a means to document trends in the population over time and complements more intensive field efforts that provide insights into the factors causing the recent severe population decline. The most recent Statewide Survey was conducted in April, 2017 and the next Statewide Survey is scheduled for April 3-5, 2020.