Survey Protocol

Thank you for volunteering to participate in the 2011 Tricolored Blackbird Survey. The statewide survey is conducted every three years in order to estimate the size of California's Tricolored blackbird population and to track changes in its distribution. This information is critical for guiding our conservation efforts and could not be accomplished without your help and the extensive efforts of other participants across the state. This protocol describes the methods to be used during the survey and provides guidance for how to report your observations.

Our goal is to develop an accurate estimate of the numbers of tricolors throughout California; therefore, we will attempt to survey for and count the numbers of breeding birds across the entire range of the species in California.

I. Scouting

It is very useful to check on your survey sites and search the surrounding areas prior to the official survey. This should make your field time most efficient and allow you to spend more time at the colonies that require the most effort to observe and count. By April 1, most colony locations will already be occupied by breeding birds, and a few southern colonies may already have nests containing young. Pre-survey observations also provide an opportunity to estimate the numbers of birds at colonies and allow you to become familiar with tricolor behavior.

II. Timing

The 2011 survey will be conducted from April 15th to the 17th. All observations that will be reported as part of this year's survey should be carried out on these dates. The locations of breeding colonies may change within periods of only a few days, so conducting the survey in a narrow time window helps to ensure that we are not counting the same birds more than once.

Subsequent observations at any future date should also be noted and recorded here on the Tricolored Blackbird Portal (http://tricolor.ice.ucdavis.edu).

III. Survey Locations and Priorities

We have placed the locations of all known breeding colony locations on to maps that may be downloaded by you prior to the survey. In some cases, these locations represent colonies that were known to be active decades ago, but have been updated to reflect new colony locations through the 2010 field season. Each volunteer team has been asked to survey a defined area within a county and, in most cases, to visit specific colony sites that were previously reported. The following are the areas that should be surveyed in priority order:

Priority One: Sites known to be active during the two previous statewide surveys in 2005 and 2008. Survey each of these sites and estimate the number of breeding birds at occupied sites. The maps are labeled with the recognized colony names.

Priority Two: Suitable habitat in areas around documented colony locations. Indicated by unlabeled points on the maps provided.

Priority Three: Other areas in the county where there is suitable habitat.

IV. Survey Protocol

Viewing the colony

NOTE: it is best to avoid any disturbance to nesting birds, as disturbance, especially early in the breeding cycle, is known to cause nest failure. Tricolored Blackbirds and other colony-nesting species may be especially vulnerable to disturbance. Under no circumstances should you enter the colony; rather, colonies should be surveyed from a distance at which the birds are unaffected by your presence. Since colonies may be located in a variety of contexts, it is up to the observer to determine how close is too close. Under most circumstances, colonies can be surveyed from just outside the boundaries of the vegetation in which the birds are nesting. The majority of sites will be readily viewed from public roads and allow close and thorough study. Sometimes roadsides provide an elevated view of a colony, and thus a better perspective from which to estimate colony dimensions and numbers of birds.

Private property should also be respected. Do not enter private property unless you have received permission to access from the landowner.

Colony Names

Use the colony names given in the list of colonies that you have been provided and that have been used to label the colonies on the maps. If you find birds nesting in a new location (one not already entered in the Portal and not on the list of colonies provided), please give the site a distinctive and easily-remembered name. Do not use the name of the landowner in colony names, and please provide directions to all new colony locations.

Latitude and Longitude

Do not record the geographic coordinates of known location; however, if you find birds nesting in a previously unknown location and have a GPS unit, please record the latitude and longitude values as well as the datum used by your GPS unit (the default for most GPS units is WGS84, but in some cases they may be set to NAD83). If you do not have a GPS unit, there are two ways to identify and record the coordinates. First, when entering your new location on the Tricolored Blackbird Data Portal, you can use the built-in Google Maps tool to zoom in and place a marker at the location. The latitude and longitude will automatically be entered when you do this. Alternatively, you can use Google Earth, an extremely useful and user friendly, free global mapping tool. Search for and zoom into the location in Google Earth, insert a placemark at the location (be sure to move the marker to the actual spot), and the latitude and longitude will be recorded in the “Properties” of that marker.

Duration

Please record the amount of time you spend at each location, including those there are unoccupied. Spend as much time at each colony as you need to get your best estimate of the number of birds. If after 10 to 15 minutes at a known colony location you have not seen any Tricolored Blackbirds, record the site as unoccupied and move on to the next location or region. If tricolors are present, use your own judgment to determine how much time to spend at the colony. In general, prolonged viewing of a colony will improve your estimate and the larger the colony the more time should be spent. This is particularly true for very large colonies (> 10,000) where it may take some time to evaluate the number of birds. With such large colonies, the more time you spend at the colony, the more the apparent chaos will give way to a semblance of order, enabling you to better estimate the size of the colony and gather observations of singing males, nest-building females, adults feeding chicks, or fledglings.

However, the time spent at one colony is at the expense of visiting more areas and documenting additional colonies. Do not spend too much time at small colonies where you can estimate the number of birds quickly. In this case, finding and counting new birds will be more valuable for the statewide estimate.

Colony Size

A Tricolored Blackbird colony can range from 20 birds to 100,000 or more birds. For this survey, all estimates will be based on visual counts of the birds at a colony. For small colonies, precise counts can be made, but in larger colonies a visual estimate will be necessary. The method used should be indicated on the data sheet.

Precise Counts

For small colonies (approximately less than 200 birds), a precise count of the number of birds will usually be feasible. With care, this should provide a very precise estimate of the number of birds present.

Scanning Surveys

When large numbers of birds are streaming by, dropping into vegetation, and are otherwise extremely active, precise counts will be impossible. To estimate the number of birds in large groups during this survey there are two ways to estimate number depending on whether birds are flying by or within the colony.

  1. Within the colony: for birds that are perched or flying around within the colony, it is effective to count the number of birds that fill a specific, repeatable field of view, such as the field of view in your binoculars. Within this field of view, either count precisely or by fives or tens for more dense concentrations, to obtain a reasonable estimate of the number of birds within that view. Then, multiply that number by the number of fields of view that comprise the entire flock or colony.
  2. Flying in Transit: Depending on the time of day and colony status, there may be streams of birds flying between the colony and an off-colony food or water source. In this case, the number of birds in these flight paths can be estimated by counting the number of birds that move by in a given amount of time and multiplying this by the total time it takes for the flock to pass.

In many cases observers will need to employ both strategies. Position yourself somewhere with good visibility and use a timed count of the flying birds as they leave the colony. Once the flow of departing birds has dropped off, then conduct a scanning count of the visible birds remaining within the colony itself. The scanning count of the colony should be repeated a few times to improve the estimate. Add the estimate of birds flying away from the colony to the count of birds within the colony. There is space on the data sheet to record your best estimate of birds, as well as what you think the minimum and maximum number of birds are at the colony. These minimum and maximum estimates will give us some sense of how accurate you feel your best estimate is.

Estimating the size of large colonies can be very challenging, and for some, frustrating. Remember that you are providing us with an approximation of colony size and not an exact count. All large colonies that you find will be revisited by one or more experts, regardless.

Sex Ratio

The accuracy of the count will also depend on the sex ratio of birds observed and this depends on activity at the colony. Some colonies that are just forming will have both males and females active so that most individuals can be seen. Once incubation begins, however, it will be mostly males that are seen. This information is critical to record. The data sheet includes space for specifying the ratio of males to females seen and whether the colony is active but quiet (indicating incubation may have begun). Tricolored Blackbird flocks often separate into groups of males and females. A quick estimate of the numbers in each sub-flock can be used to determine an overall sex ratio. Estimate the ratio of males to females in several sub-flocks or fields of view and average them to come up with an estimate.

Colony Observations

Locating new colonies and estimating colony sizes are the primary goals of the survey; however, the characteristics of colonies, the surrounding environment, and the behavior of the birds are all valuable for assessing the status and health of colonies.

Nest Substrate

Observers should record the substrates in which nests are built. There is space on the data sheet to record both primary (dominant) and secondary substrates. Tricolored Blackbird native habitats consist primarily of young freshwater marsh dominated by tules or cattails, but they also nest in a variety of other vegetation types that provide enough structure and cover to build nests. In addition, they also now regularly nest in grain crops, particularly triticale fields in association with dairy farms. Likely substrate plants are: bulrush/tule, cattails, Himalayan blackberry, milk thistle, stinging nettle, and triticale. Other substrates include willows, cottonwood, Arundo donax, desert olive, mustard, prickly lettuce, mule fat, coyote brush, raspberry, tamarisk, and poison hemlock.

Colony Surroundings

In addition to locating and viewing the colony, it is useful to describe the surroundings. In addition to nesting substrate, Tricolored Blackbirds also require a source of open water and suitable foraging areas (e.g. upland pasture, grassland, alfalfa). They can fly several miles to sources of abundant food (like farms with stored grains). Knowing about these locations will assist in future surveys and may help observers to find additional breeding colonies as birds move between various nesting sites and a centralized food source. Any stream of blackbirds is worth following! On the data sheet, if source of water or stored grains are identified, please record the presence of stored grains nearby and the distance to water. Also, note the dominant land use surrounding the colony (type of agricultural crop, natural vegetation type, etc).

Colony Area

Observers should try to record the approximate length and width of the breeding substrate within the colony. These measures will be used to calculate the total area of the colony. Since breeding substrate often occurs in patches over a larger area, size estimation is approximate. Colony area will be used with what is known about the average nest density within Tricolored Blackbird colonies to develop a secondary estimate of the number of birds in the colony.

  • Measuring Width and Length: Where possible, observers should pace out two sides of the colony, using strides that approximate one meter. Record the number of meters for these two sides on the data sheet.
  • Aerial Photos: Using satellite photos that are provided, observers can highlight the boundaries of the colony being used. These marked-up photos should be sent in with paper copies of datasheets following the surveys. These will provide a means for mapping the extent and calculating the total area of colonies observed.

Behavior and Colony Status

Behavior of birds at a colony and the current activity at the colony are also important sources of information for understanding the seasonal timing of breeding and success of particular colonies. Important observations to record on the datasheet include:

  • Singing: pronounced chorus of males heard singing at a colony
  • Carrying Nest Material: females observed carrying nest material (e.g. grass)
  • Colony Quiet: if the colony is relatively quiet (no singing or large groups of males and females moving about) and primarily males are visible, this may indicate that incubation has begun and females are on eggs.
  • Carrying Food: adults observed carrying food (usually insects protruding from bill)
  • Fledglings: observed young birds in association with adults.

Documenting the Locations of New Colonies

Documenting the locations of new colonies is essential if we are to comprehensively monitor the tricolored blackbird population. Please use the street and colony maps provided (or another map you have available and can copy) to mark the location of new colonies and be sure to enter records for these new locations into the Portal.

Survey Routes

Use the maps provided or other maps that you have available to indicate the routes taken during the survey by highlighting the roads and areas surveyed. These should be sent in with the datasheets and aerial photos following the survey.

Total Survey Time and Mileage

Please record the total time, number of observers in your team, and miles you drove for the survey. These can be recorded separately and emailed to Keiller Kyle, the 2011 Tricolored Blackbird Statewide Survey coordinator (kkyle at audubon dot org).

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2011 TRBL Survey Protocol.doc55 KB