Characteristics of a River Otter (Lontra canadensis) Maternal Den in the Central Platte River Valley, NE

Abstract

River otters (Lontra canadensis) encompass a broad geographic range including coastal, riverine, and lacustrine systems. However, knowledge of reproductive behavior and structural den characteristics remain relatively few in the literature, particularly in the Great Plains. Distinctions between the terms “den”, “den site”, “natal den”, and “maternal den” are often ambiguous, obscuring our understanding of river otter’s young-rearing behavior. We used observations and descriptions regarding a single maternal den site and a broad reading of the mustelid literature to propose a more standardized maternal den definition for river otters and specify hypotheses for future research. From 25 April to 13 May 2019 and from 4 April to 30 April 2020, we recorded observations of parental behavior, such as relocation of young to a maternal den and aquatic acclimation, via direct or video surveillance. We also systematically assessed habitat and site characteristics associated with this maternal den. We estimated that the river otter young were relocated to the maternal den between 6 to 8 weeks of age, placing them at 8 to 10 weeks at the time of their first observed aquatic acclimation. The maternal den consisted of a distorted metal pipe (entrance = 9 cm height, 28 cm width) on the bank of an excavated perennial pond within 100 m of multiple anthropogenic structures (i.e. cottage, office), but considerable distance from the Platte River (441 m). The maternal den was located adjacent to a small pond (length = 66.4 m, width = 15.2 m, max depth = 69 cm) on a moderate bank slope (29.5%) in relatively dense herbaceous (x̄ cover = 55.0%, x̄ height = 0.53 m) and woody (x̄ cover = 37.5%, x̄ height = 1.56 m) understory vegetation. We suggest that this unique site may have provided a number of benefits including thermoregulatory advantage, predator protection, relatively stable water depth, and proximate access to resources. We suggest that river otter maternal dens are sites used subsequent to and exclusive of parturition that proceed weaning where females continue to exhibit denning behavior as young are still largely dependent and in the earliest stages of developing motor and survival skills. We hypothesize that a set of interrelated factors distinct to particular juvenile life stages promotes maternal den site selection. This represents the first detailed description of a river otter maternal den and den site reuse in the Central Platte River Valley (CPRV), Nebraska and a rare description from the Great