Northern Prairie Wildlife Research Center
| 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. |
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://www.npwrc.usgs.gov/resource/birds/depred/table7.htm
Page Contact Information: Webmaster
Page Last Modified: Friday, 01-Feb-2013 19:10:51 EST
Menlo Park, CA [caww54]
