Northern Prairie Wildlife Research Center
Evaluations of Duck Habitat and Estimation of Duck Population Sizes with
a Remote-Sensing-Based System
Duck Populations
We restricted our analysis of annual change in ponds, duck population sizes, and
duck production to 10 waterfowl management districts (Fig. 1) for which we had
aerial video data during 1987-90. Although video was obtained of other waterfowl
management districts as they were added to the remote-sensing-based system, the
lack of data in some years would have confounded comparisons among years.
Regression Estimates
Estimates of breeding-population sizes were derived from a regression model.
Data for constructing baseline regressions for all species except wood ducks
(Aix sponsa) were gathered at the Arrowwood Waterfowl Management District
(1982-84). For wood ducks, we used data gathered at the Fergus Falls (1986-87)
and Detroit Lakes (1987) waterfowl management districts. Baseline regressions
were constructed by regressing the number of pairs observed on each pond on
the size and the square root of the size of the pond. The general form of the
equations was:
Wet area in this equation is the wet area in each pond. (Estimates
of the regression coefficients A and B are presented in Table 3, and the regression
curves are presented on Fig. 2).
Ground Counts
The boundary of each wetland basin where breeding-pair counts were conducted
was delineated on aerial photographs, and a unique identification number for
the naming of the polygon of that basin was placed on the photograph.
Table 3. Baseline regression coefficients used for estimating breeding
duck (Anatinae) populations on 10.4-km² plots from the area (ha) of individual
ponds determined from airborne video in the prairie pothole region of the United
States, 1987-90.
| |
Regression coefficientsa |
|
Species |
A |
B |
| Mallard |
0.0106 |
0.2899 |
| Gadwall |
0.0341 |
0.2848 |
| American Wigeon |
0.0000 |
0.0193 |
| Green-winged Teal |
0.0000 |
0.0431 |
| Blue-winged Teal |
0.0000 |
0.7376 |
| Northern Shoveler |
0.0136 |
0.1870 |
| Northern Pintail |
0.0000 |
0.1866 |
| Redhead |
0.0410 |
0.2233 |
| Canvasback |
0.0064 |
0.0453 |
| Lesser Scaup |
0.0173 |
0.0528 |
| Ring-necked Duck |
0.0022 |
0.0110 |
| Ruddy Duck |
0.0119 |
0.1226 |
| Wood Duck |
0.0064 |
0.5612 |
aPairs = A x wet area + B x wet area.
The pair count was conducted by a person who walked around each pond. Pairs on
lakes and rivers were sometimes surveyed from a boat or from a canoe. When dense
emergent vegetation was present, the observer moved through the vegetation and
flushed the birds. Sample ponds were more widely dispersed in the remote-sensing-based
system than in surveys that are often conducted on plots or transects. We assumed
that sample ponds were usually far enough apart to prevent the flushing of birds
from one sample pond to another. Social groups were recorded on field forms designed
for data entry into a microcomputer. Data were entered soon after completion of
the counts. Error checking was done by a series of custom-designed programs that
were executed at the time of data entry and immediately after data entry. The
size of a breeding population was expressed as the estimated number of breeding
pairs, which included observed breeding pairs and pairs that were inferred from
other social groups. We followed approximately the same techniques described by
Hammond (1969) and Dzubin (1969). The estimated number of breeding pairs was estimated
by the computer at the time of data entry as follows: 1 observed pair = 1 estimated
breeding pair; 1 lone male = 1 estimated breeding pair; 1 lone female diving duck
= 1 estimated breeding pair; each flocked, male dabbling duck in flocks of five
or fewer individuals = 1 estimated breeding pair except in wigeons and in northern
shovelers for which the number of flocked males was not converted to estimated
number of breeding pairs; each flocked female diving duck in flocks of five or
fewer individuals = 1 estimated breeding pair. Flocked birds in flocks with more
than five individuals were not used to estimate the number of breeding pairs.
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