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

Appendix B, Table 2


Table 2. Comparison among principal predators of duck nests in the Prairie Pothole Region of various types of evidence found at duck nests destroyed by predators. Indicator rating of depredation by each species are positive (P), negative (N), inconclusivea (I), or not applicableb (na). Indicator ratings are based on available data and authors' experience and are for nests with ≥6 eggs when destroyed.
  Principal predators
Evidenceb Coyote Red fox Raccoon Striped skunk American badger Mink Weaselsc Franklin's ground squirrel Black- billed magpie American corw Large gullsd
Hen killed
Feathers or blood only P P N N N P N, Ie N N N N
Carcass or carcass parts P N N N N P N, Ie N N N N
Cranium intact if present P na na na na N na, Ie na na na na
Cranium punctured if present N na na na na P na, Ie na na na na
Nest materialf
≤1% displaced P P P N I P P P I P P
1-10% displaced on ground P P P I I P P P P P P
11-30% displaced on ground P I I P P N N I P P I
>30% displaced on ground P N N P P N N I P P N
>1% displaced aerially N N N N N N N N P P I
Ground surface disturbance
≥1 dug area N N N N P N N N N N N
Number cached or whole cells
Evidence of ≥1 cached egg N N N N P N N N N N N
≥1 uncached whole egg P N N N P P P P P P/Ng P
Number of eggshells
No eggshells I P N N N I P P P P N
Eggshells of <50% of clutch P N N N P P P P P P N
Eggshells of ≥50% of clutch I N P P I N N N N I P
Amount of shell fragments
None I P N N N P P P P P N
Trace P N N N N P P P P P N
>trace but <1 egg P N P P P P I P I P P
≥1 egg N N P P P I I P N P P
Damage to eggshellsh
All have small holes P na N N N N P N P P I
≥50% have small holes and all others have large holes or are fractured P na N N N N P P P P P
≤50% have small holes and all others have large holes or are fractured I na P I N P P P P P P
All eggshells have large holes or are fractured N na P P P P N P N I I
≥1 trampled eggshell N na P N P N N N N N N
≥1 crushed eggshell N na N N P N N N N N N
Location and number of openings in eggshellsh
All openings on side P na N P N I I I P P P
Mix of openings on side and side-end P na I P P P P P P P P
≥1 opening on side and 1 on end, but <50% on end N na P P I I I P I I N
≥50% of eggshells with opening on end N na P N N N I P I N N
≥1 eggshell with ≥2 openings P na N N N N N N I P P
Puncture marks and serrated edges
≥1 eggshell with numerous small puncture marks N na N N N P P N N N N
≥1 eggshell with finely serrated edge of opening N na N N N N P P N N N
Amount of conspicuous yolk residue
No eggshell has residue P na P P P I I I N I N
>1 eggshell has residue N na N N N P P P P P P
≥50% of eggshells have residue N na N N N I I N P N P
≥1 eggshell has ≥25% of egg contents N na N N N I I P P P P
Locations of eggshells
None in nest P na P P P P P P I I P
All in nest P na I I N N N N N N N
≥1 outside nest but all ≤20 cm from nest P na P P N N N N I I N
≥50% of eggshells >1 m from nest P na N N N I I P P N N
Distrubance to vegetation at nest
No disturbance P P N N N I P P P P P
Matted area >1 m from nest but not connected to nest by trail P N N N N N N N N N I
Matted area or wide trail <1 m from nest N N P P P N N N N N N
Wide trail extending out 1-3 m from nest N N N N P N N N N N N
Narrow runway(s) leading away many meters from nest N N N N N P P I N N N
a Information is inadequate to assign an indicator value to the evidence or the evidence has little value in deciding if the predator species caused the destruction.
b See glossary for definitions of terms; na = not applicable because eggshells or evidence hen was killed are customarily absent.
c Includes ermine and long-tailed weasel.
d Includes ring-billed gull and California gull.
e First entry is the response for the ermine; second entry is the response for the long-tailed weasel.
f In making assignments we took into account that the proportion of nest material displaced from artificial nests in our studies (Table 5) probably exceeded that at natural nests because the material was not packed as tightly as at natural nests.
g Positive indicator if egg(s) are in nest, but negative indicator if ≥1 egg is outside nest.
h For nests at which ≥6 were found.

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