Diel activity patterns of river otters (Lontra canadensis) in southeastern Minnesota

An understanding of activity patterns of wildlife in relation to abiotic and biotic factors enables biologists to better understand the ecology of species, manage resources, standardize survey methods, and serve as an index of the relative density of a species. River otters (Lontra canadensis) were radiotracked between June 2002 and October 2003. Using radiotracking data, we conducted exploratory analyses to determine relative influence of abiotic and biotic factors on 2 measures of activity of otters. Abiotic factors included air temperature, barometric pressure, lunar phase, biological season, and time of day; the biotic factor was sex. Activity was measured indirectly via movement rates and directly as the proportion of location attempts recorded as active (PLA). Movement rate was defined as the distance traveled by an otter between consecutive location estimates. Generalized linear mixed models were used to explore the influence of covariates on both measures of otter activity. The model best explaining variation in movement rate included biological season, sex, a season*sex interaction, and time of day. Males moved at greater rates than females during breeding and winter seasons but moved at similar rates to females during summer. Covariates found to account for most variation in the PLA of otters included time of day, season, and temperature. Otters were active throughout the day but with bimodal peaks in the PLA during late evening and early morning hours. The PLA of otters was highest during breeding season, lowest during winter, and intermediate in summer months. In addition, the PLA of otters decreased slightly with increasing temperature. Overall, the PLA of otters in our study area was influenced by abiotic factors, and movement rates of otters were influenced by abiotic and biotic factors.