Graduation Date
Spring 2025
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Wildlife
Committee Chair Name
Jeffrey Black
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Second Committee Member Name
Micaela Szykman Gunther
Second Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Third Committee Member Name
Frank Fogarty III
Third Committee Member Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
Wetlands, River otter, Waterfowl, Ducks, North American river otter, Waterbirds, Behavior, Antipredator, Prey, Predator, Prey selection, Arcata Marsh and Wildlife Sanctuary, Marsh
Subject Categories
Wildlife
Abstract
Generalist predators are assumed to take a wide variety of prey throughout an annual cycle, often switching between food sources depending on availability. Prey selection is often studied by way of variables such as prey age class, body size, and various topics related to anti-predator behaviors, all variables used to measure how predators target prey. Following prior studies in coastal Northern California documenting that river otters (Lontra canadensis) had selected waterbirds as prey, we identified undigested prey items in scat to evaluate prey selection of waterbirds at the Arcata Marsh and Wildlife Sanctuary (AMWS). We compared feathers found in river otter scat with museum specimens to determine if waterbirds were taken in relation to their availability. Bird feathers were present in 15% or more of the river otter scat in 7 of 12 months (October 2022 through April 2023) and were the most frequently observed prey type in December (56.5%), January (61.9%), and February (59.4%), whereas fish were the most frequent prey in other months. Scat contents revealed that 15 species of waterbirds were taken, with bufflehead (Bucephala albeola; n = 183) being most detected, followed by ruddy duck (Oxyura jamaicensis; n = 167), American wigeon (Mareca americana; n = 116), American coot (Fulicula americana; n = 81), mallard (Anas platyrhinchos; n = 38), and green-winged teal (Anas crecca; n = 35 ) in the top 6, making up 90% of birds taken. River otter predation of waterbirds did not always occur in relation to their availability, and we considered anti-predator tactics and life history traits as drivers of waterbird selection. Waterbirds considered more susceptible to predation were consumed more often. River otter selection of more vulnerable species was associated with less effective anti-predator tactics such as remaining motionless, latency to fly, and attempting to escape by diving. Remaining alert and taking flight was considered effective in lowering the risk of predation. Freezing in place within a pond and clustering in an area where otters have the advantage underwater, was not. Species known to breed and undergo a flightless molt at AMWS also experienced predation by river otters. This study demonstrates the importance of considering life history parameters when evaluating predator-prey relationships and the complexities of prey selection by river otters.
Citation Style
JWM
Recommended Citation
Culver, Gina Yael, "North American river otter (Lontra canadensis) prey selection of wintering waterbirds in a wetland complex" (2025). Cal Poly Humboldt theses and projects. 2299.
https://digitalcommons.humboldt.edu/etd/2299
Included in
Environmental Education Commons, Natural Resources and Conservation Commons, Natural Resources Management and Policy Commons