I compared the foraging sites of Black
Dryocopus martius and White-backed
Dendrocopos leucotos woodpeckers and developed methods to distinguish between them during winter. Only
D. martius foraged on conifer tree species. The DBH of trees used for foraging by
D. martius were larger than those used by
D. leucotos. Foraging rates on dead wood, including snags and logs, were similar for both species; however, only
D. martius foraged on live trunks, whereas
D. leucotos foraged on mostly dead branches.
D. martius pecked off larger wood chips and bark pieces while foraging than did
D. leucotos. The widths of beak marks left at foraging sites were indications of woodpecker species; they did not vary with sex, hardness of wood chips, or tree species. The widths of beak marks (sampled from foraging trees) were 4-7 mm for
D. martius and 2-5 mm for
D. leucotos. Thus beak marks of more than 6 mm were those of
D. martius. When three beak marks were sampled from a foraging site, the median width of
D. martius was 4-6 mm compared with 2-4 mm for
D. leucotos. Therefore, beak marks of more than 5 mm were left only by
D. martius. The probability that the median width (of three beak marks) of
D. martius' beak marks at a foraging site is more than 5 mm is estimated to be 0.904 with 95% percentile confidence interval (0.788-0.988) by bootstrapping. To distinguish between
D. martius and
D. leucotos foraging sites, a tree-based model was used. The first node classified the largest wood chips more than 13 as foraging sites of
D. martius. The next node confirmed that live trunks were the foraging sites of
D. martius and that dead branches and trunks, and live branches were the foraging sites of
D. leucotos. Measurements of museum specimens confirmed that the bill of
D. martius is larger than that of
D. leucotos.
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