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Depredation Patterns of Predator Species

American Badgers

Badgers forage in uplands. They likely depredate duck nests in all upland habitats but seldom depredate nests over water (Sargeant and Arnold 1984, Brandt 1994).

Response to Hens and Nests--Badgers are not known to capture hens (Sargeant and Arnold 1984). We never observed any badgers encounter duck nests and found no descriptions of such in the literature.

Treatment of Eggs--We found no descriptions of depredations of eggs by badgers. Our examination of records of natural nests destroyed by predators produced 61 records with at least 1 egg cached ≥2 cm under soil and/or debris at the nest. We believe this is a characteristic solely of badgers and therefore attributed destruction of those nests to badgers. Those nests contained 571 eggs when last visited by investigators about 1 week before the nests were discovered destroyed. Assuming 571 eggs were present when the nests were destroyed, we accounted for 234 (41%) eggs from eggshells and 57 (10%) from whole eggs found at the nests (includes uneaten cached eggs). Whole eggs not cached (1-3/nest) were found at 9 (15%) nests, suggesting that badgers often partially depredate duck nests. Many missing eggs were represented by shell fragments. Other missing eggs may have been completely eaten, or may have been cached and not discovered by the investigators. We do not know the frequency badgers cache ≥1 eggs at the nest sites.

Investigators found evidence that 116 eggs were cached at the nests described above; only 37 (32%) were still in caches. Remaining eggs had been retrieved and eaten, presumably by badgers. Badgers customarily cached only part of a clutch; ≥1 egg was eaten at 58 (95%) nests. Badgers usually cached eggs individually, but there were 5 instances of 2-4 eggs cached together. Badgers customarily cached eggs in small freshly-dug holes (Fig. 3); there were 2 instances of eggs cached in the nest. Depth of covering over the deepest cached egg was ≥5 cm at 33 (54%) nests; maximum depth was 14 cm.

Figure 3. Duck egg assumed to have been cached by an American badger at a duck nest. Egg was partially uncovered by the investigator.

Appearance of Eggs and Nest Site--We obtained data on damage to shells of 265 duck eggs assumed to have been depredated by badgers (Appendix B, Table 3), 169 from nests from the investigated file and 96 from the 17 other natural nests at which cached eggs were found by coworkers. Most of 265 eggshells had large holes (40%) or were severely damaged (57%) (Appendix B, Table 3). Openings in eggshells usually were asymmetrical with coarsely broken edges and numerous pieces of shell caved inward (Appendix C, Fig. 5c-e, g-i). Badgers often crushed a duck egg within their mouth, resulting in crushed eggshells (Appendix C, Fig. 5l). Nine (24%) of 38 eggshells found at 7 nests with prevalence of crushed eggshells reported were crushed.

We obtained data concerning location of openings in 79 eggshells of duck eggs assumed depredated by badgers (Appendix B, Table 4), 33 from 14 nests in the investigated file, and 46 from 17 other natural nests with cached eggs. Most had an opening in the side (30%) or a side-end (61 %) (Appendix B, Table 4). Eggshells of eggs depredated by badgers seldom had puncture marks or puncture holes, or conspicuous yolk residue.

There were dug areas at all 61 nests destroyed by badgers because eggs had been cached. Dug areas >10 cm diameter were found at 36 (59%) nests. We do not know the frequency of badger digging at nests, but assume digging usually is associated with egg caching.

The proportion of nest material displaced from 61 nests destroyed by badgers ranged from 0 to 100%, and was >30% at 32 (52%) nests (Appendix B, Table 5). Large size and squat physique of badgers often resulted in considerable matting of vegetation at nests, especially where eggs were eaten. Badgers often made wide trails at and/or near nests.

Most (89%) of 173 eggshells found at 61 nests destroyed by badgers were ≤1 m from the nest, 74 (43%) were ≤20 cm (including in nest) from the nest (Appendix B, Table 6). Eggshells outside nests usually were to 1 side of the nest site.

Conclusions--Of the principal predators, badgers cause the most disturbance at nest sites. Cached egg(s) at the nest, especially if covered by ≥2 cm of debris, implicates badgers in nest destruction. Other indications of badgers include finding at the nest most or all of the following: (1) part of clutch missing without trace, (2) most eggshells have a large hole or are severely damaged, (3) crushed eggshell(s), (4) ≥50% of openings in eggshells in a side or side-end, (5) dug area, and (6) >30% of nest material displaced on ground (Appendix B, Table 2).

Evidence that indicates a nest was not destroyed by badgers includes finding at the nest any of the following: (1) evidence the hen was killed, (2) all eggs missing without trace, (3) eggshell with a small hole, or (4) aerially displaced nest material (Appendix B, Table 2).