By Pam Garrettson, USFWS biologist, Western Dakotas and Eastern Montana
We have now finished all the air-ground segments in North Dakota, and did our first day of surveying in Montana today. The ground crew's job is to count a sample of the segments that the air crew surveys, and the ratio of the number of ducks (by species) that we see to the number that the air crew sees is used as a correction factor in calculating population estimates. This visual correction factor (vcf) can vary by year, crew area, and species. When possible, it is calculated on an annual basis, but for rarer species, several years of data may need to be used to calculate a vcf.
To provide a comparable count, we must cover the exact same area as the air crew, 200 m on either side of the line they fly. They use marks on their airplane struts and other cues to guide them. We have it easier, aided by photographs with a line marked 200 m on each side of the survey line (photo). But when there's a lot of water and few landscape features, it can be tough. The other day I walked out into a field of flooded corn stubble to make sure I got all the birds that might be hiding there. To make sure I didn't wander past the boundary into the next county, Brent shot me. With a laser range-finder, that is.
Ideally, the air-ground segments would be chosen randomly, but in practice, they must have sufficient wetlands and ducks to provide a good comparison, and they need to be accessible by road. When possible, we count birds from the road, but we walk to wetlands and along streams that aren't completely visible, and occasional portions of segments that aren't drivable. Throughout the prairie pothole region, in both the United States and Canada, the road system is laid out on a grid system of 1 X 1 mile squares. In more populated areas, there may be a good gravel road nearly every mile, running east-west or north-south, but in our crew area, roads are few and far between, and so are our air-grounds.
Thus we have covered a lot of ground, on foot and by truck, over the past couple of weeks. Plus we drove out here from Maryland, so we put on a lot of miles before we ever started the survey. No worries though; we brought plenty of provisions, a tailgate grill, and a camp stove. Not all our fare equals the gourmet meal we made last night though. I'll confess to eating a pound of bacon and several bags of marshmallows in just a few days, and Brent has eaten pounds of sunflower seeds. We need to keep up our strength, you know.
Aerial photos used by ground crews. Photo by Brent West, USFWS
Black-tailed prairie dog in southwestern North Dakota. Photo by Brent West, USFWS
Bison in Theodore Roosevelt National Park, North Dakota. Photo by Brent West, USFWS
Get more information about the 2014 BPOP Survey and other waterfowl surveys at Flyways.us
Find more breeding waterfowl and habitat updates on the DU Habitat Map