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Breeding Grounds Survey: Calibrating for the Survey

Western Dakotas, Eastern Montana - May 02, 2014 
By Rob Spangler, USFWS pilot biologist

Brenda and I took to the air today to calibrate our transect width—to ensure we are only counting birds within 200 meters on either side of the aircraft. The survey calculations are based on this transect width, so it is very important that all flight crews calibrate their observations. To do this, we flew just north of Pierre, South Dakota, where there are a lot of agricultural pivots that are useful in measuring distance on the ground. A standard pivot has a radius of 400 meters, so half of that equates to our 200-meter limit. To calibrate our estimates, we fly at 120 feet above ground level at 90 knots and look out to our side of the aircraft–Brenda to the right and me to the left. Once we see the 200 meter mark on the pivots we notice where that point falls on the wing strut and place a piece of electrical tape to mark the distance (see photo). Now we both have a reference point to help us determine if wetland habitat and waterfowl are to be counted or excluded. Additionally, we flew over habitats that were “on the line” and tested between Brenda and myself for consistency.

Once we felt confident about our distance estimation, we went looking for waterfowl, to brush up on our waterfowl identification and to obtain of a subsample of waterfowl to determine their breeding status. If you start the survey too early, you will see large groups of migrating birds, not a lot of pairing or lone drakes, and a species composition skewed towards divers or lacking later migrants such as blue-winged teal or gadwall. Start too late and you will see large flocks of drakes. As noted by biologists I talked with from the Dakotas and Montana, the divers have moved north and we were seeing all species present and pairing occurring. Tomorrow, we will meet up with our ground crew to go out on the ground and collect data from a representative sample of wetlands to get a better idea of how things are progressing.
Electrical tape is placed on the wing strut to estimate distances based on an established pivot point of reference.

Electrical tape is placed on the wing strut to estimate distances based on an established pivot point of reference. Photo by Rob Spangler, USFWS

Sheet water present - much better conditions than last year. Photo by Rob Spangler, USFWS

Get more information about the 2014 BPOP Survey and other waterfowl surveys at Flyways.us

Find more breeding waterfowl and habitat survey updates on the DU Habitat Map