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Interpreting Evidence of Depredation of Duck Nests in the Prairie Pothole Region

Appendix B, Table 7

Table 7. Stepwise application of specified criteria to estimate the proportion of destroyed (by predators) incubated duck nests of ≥6 eggs in uplands of 48 federal waterfowl production areas in Minnesota, North Dakota, and South Dakota with destruction caused by red foxes.
    Number of nests
Criteria Indicatora Affected Remaining in sample
Nestsb     1,108
Destroyed by predator   636 636
≥6 eggs present when last visited   564 564
Eggs incubated when last visited   421 421
Visit interval of ≤14 days   395 395
Excluded becasue of missing datac   6 389d
No eggshells P 124 124
No shell fragments P 86 86e
Dug area N 2 84e
Carcass of carcass parts of hen N 3 81e
Evidence egg cached N 0 81e
≥1 whole egg N 6 75e
>30% of nest material deplaced N 3 72f
a Positive (P) or negative (N) indicators of depredation by red foxes. For each category of evidence, all nest depredation records remaining in the sample are examined for presence or absence of that evidence. Records with evidence are retained (P) for possible assignment of destruction to foxes. Records without that evidence (N) are removed from further consideration of possible assignment of destruction to foxes.
b Total nests found that were suitable for analyses (excludes nests with eggs broken of hens injured by investigators, nests abandoned within a few days after discovery, and nests parasitized by another species).
c Nests excluded because data were absent for ≥1 examined variable.
d Sample of nests used in analysis.
e Nests likely to have been destroyed by red foxes.
f Nests with cause of destruction assigned to red foxes.

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