Northern Prairie Wildlife Research Center

# Factors Associated with Duck Nest Success

in the Prairie Pothole Region of Canada

*Habitat Preference*

We used all nests of all of the 5 common species regardless of their fates to
derive habitat preference values. For each species, we pooled all nests found
in all habitat searched in each habitat class in all area-years. In combining
data in this manner to derive preference values, we accepted the following assumptions
as being reasonable: (1) that preference for nesting in a habitat by a species
is an innate behavioral preference and was similar in all area-years and (2) that
our procedures to find nests were about as effective in all habitats and all stages
of nesting.
We used a linear model (Appendix B) to estimate nest
densities among habitats and study areas; large differences existed in amount
of habitat searched and in numbers of nests found in some habitats in some area-years.
A key feature of this model, like the model we used to improve our estimates
of daily survival rates (DSR's) in the following section, is that habitat effects
did not interact with other effects.

We included in the model effects for area-year, half-area-year within area-year,
habitat, and number of nest searches. Number of searches was included because
not all habitat polygons could be searched 3 times (e.g., stubble fields in
Cropland usually could be searched only once before they were tilled). We used
a transformed variable, log([*N* + 0.0001] ÷ *A*) as the dependent
variable, where *N* is the number of nests found for a species and *A*
is the area searched. The log transformation was invoked because we believed
the effects of the explanatory variables were more likely to be proportional
than additive. We added 0.0001 to avoid difficulties involved with taking the
log of zero. We fitted the linear model by the method of weighted least squares
(Snedecor and Cochran 1980) with weights equal to the product of number of breeding
pairs and area of each habitat class searched in individual half-area-years.
Theoretically, these weights reflected the relative precision of each density
estimate. Habitat preference values were calculated by scaling least-squares
estimates of habitat effects so that they summed to 1.0.

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