Hind paw of a fisher (Pekania pennanti)

Fishers have plantar glands within whorls of hair on their hind paws that emit a distinctive odour (note that distinctive does not necessarily mean pungent).(1)(2)(3)(4) They appear as small dark circular patches on the large segmented centre pad (known as the metacarpal pad).
The plantar glands of pregnant female fishers enlarge to >10mm during January through May, and reduce in size (<10 mm) during June after giving birth. On males, the glands increase in size from <15 mm in December to >30mm in May. Reduction of the gland size is complete by June. Because these glands enlarge near and during mating season, it is hypothesised they serve the purpose of creating a trail of scent for fishers to locate each other for mating.(3)
Most marten species also have visible patches on their hind paws that are associated with plantar glands.
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