Northern Prairie Wildlife Research Center
Comparison of Historical and Recent Prairie Waterfowl Nesting
Data to Determine Trends in Nest Success
WENDY D. BEAUCHAMP AND THOMAS D. NUDDS
Department of Zoology, University of Guelph, Guelph, ON
N1G 2W1, Canada
It has been hypothesized that (1) nest success is a "bottleneck" limiting growth
of duck populations in the Prairie Pothole Region of North America and (2) increased
predation pressure resulting from degradation of upland nesting habitat by agricultural
practices has led to insufficient nest success to maintain certain waterfowl
populations. It has been assumed that this trend can be reversed and that nest
success, and thus population size, can be increased by reducing losses to nest
predators through management techniques which deter predators. Before the effectiveness
and cost-benefit of these management plans can be assessed, it needs to be determined
if nest success has in fact declined in the prairies in the past few decades.
We investigated historical trends in nest success of prairie ducks by analyzing
existing data from the literature. Until recently, comparative studies of this
type were difficult to undertake because incomparable methods of estimating
nest success have been used in different studies. However, Green (1989) proposed
a transformation procedure which can be used to convert the conventional "apparent"
nest success estimators to "Mayfield-equivalent" success values, which can then
be compared with actual Mayfield nest success estimates of more recent studies.
We have calibrated this conversion equation using data from two published studies
on waterfowl which report both apparent and Mayfield estimates determined from
original nest search data. We found that Green's equation introduces little
error (5 %) into the conversion of apparent nest success to Mayfield nest success.
This error is less than both (1) the difference between apparent nest success
and Mayfield nest success estimates when no transformation is made (15%) and
(2) the magnitude of the presumed historical decline in nest success. Preliminary
results of our analysis of published data of nest success are presented. It
is important to consider that even under "ideal" conditions, some nest loss
is inevitable and it is necessary to ascertain what the "normal" rate of nest
success is before trying to decide to what extent it can be improved upon by
management of predators.
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