Waterfowl Surveys

Flock of waterfowl at Sutter NWR by Mike Peters

Waterfowl surveys have historically been conducted bi-monthly by refuge biologists from October through February. Starting fall 2016, surveys will be conducted once-monthly. Please note that wildlife regularly move around the Sacramento Valley.

The latest Waterfowl Surveys

Check out the Waterfowl Status Report by the USFWS and Canadian Wildlife Service.

2020-21 Season: 
Surveys are done once a month, around mid-to-late month.  It takes approximately 7-14 days for biologists to transcribe and post survey results.

How are surveys conducted?

Wildlife surveys are conducted once a month, mid-month, on all wetland refuges of the Sacramento NWR Complex.  All waterfowl, shorebirds, waterbirds, gamebirds, raptors, and a handful of mammals and other songbirds are tallied on every single unit (pond/field), using a standardized survey route, a window-mounted spotting scope and binoculars. Using the same observer for each refuge helps maintain consistency (some of the biologists have maintained their routes for over 20 years), assuring a strong index over time.

Routes are designed to take advantage of vegetation barriers, viewing lanes, and flight patterns to maximize viewing, reduce disturbance, and increase the likelihood that flushed birds will fly to an area that the observer has already counted. The observer approaches each pond and takes an initial count. When numbers per pond are low (in the hundreds), a count of each species is done separately. When numbers per pond are in the thousands, all species except for ducks are counted separately, and then ducks are counted as one group and a species composition is applied to that group (ie 1% mallard, 4% gadwall, 10% shoveler, 20% wigeon, 25% green-wing, 40% pintail).  Composition can change even within a pond, as some species such as teal will concentrate in certain areas, so multiple groups may be counted and described with different compositions across a single pond.

Depending on flock size, birds may be counted as singles, or in groups of 5, 10, 20, 50, 100, or even 1000 (the only option when a group of 20,000 birds take flight). The smaller the grouping that the observer uses for counting, the higher the accuracy.

Each pond/field is scanned from multiple viewing points, with the goal of seeing and counting all visible wildlife.  Auditory cues can also be used, especially for secretive marsh birds such as rails or bitterns.

Following a survey week, biologists transcribe their data and enter it into a database. This data is then used to analyze bird use of each pond/field, and can be tied to management data to assess the effectiveness of past treatments, or identify the need for future efforts. It helps managers identify units that are critical for supporting wintering waterfowl, breeding birds, or special status species, which in turn guides decisions when facing drought, water restrictions, invasive species or other threats. When rolled up to the refuge level, population trends and distributions over time can be assessed. The data is also pulled to feed into larger survey efforts for a variety of species groups at a statewide level.



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