Muskrats and Waterbirds

Gross, R., S. Tucker, B. J. Darby, and S. N. Ellis-Felege. 2017.Trapping efficiency and incidental take of waterbirds using covered and uncovered floating muskrat sets. Wildlife Research.

Project Background and Findings

Muskrats (Ondatra zibethicus) have been a highly sought after furbearer species in North Dakota because of recent pelt prices. In 2011, regulation changes allowed trappers to use float sets to trap muskrats during the spring season. The current regulations require float sets used during the spring trapping season to have a covering made of either wire mesh, wood, or plastic and must not have an opening exceeding 20.32 cm (8 in) to attempt to minimize the incidental take of non-target species.

The primary goals of this project were to determine if muskrat float set covers are effective in eliminating incidental take of non-target species and to compare trapping efficiency at covered and uncovered float sets. The study was conducted over a two year period in an area used heavily by migrating waterfowl in eastern North Dakota. Float sets used included uncovered, 2.54 cm by 2.54 cm (1 in x 1 in) wire mesh, and 15.24 cm by 15.24 cm (6 in x 6 in) wire mesh float sets. Trapping efforts were focused to four areas: Devils Lake Basin, Arrowwood National Wildlife Refuge (NWR) and Chase Lake Wetland Management Districts (WMD), and Tewaukon NWR. During the study, 490 muskrats (157 on uncovered, 124 on 1 in x 1 in, and 209 on 6 in x 6 in) and seven non-targets species (three black-crowned night heron (Nycticorax nycticorax), two blue-winged teal (Anas discors), and two painted turtles (Chrysemys picta)) were captured over 4,245 trap nights. All non-targets were captured on uncovered float sets except for the painted turtles (1 in x 1 in and 6 in x 6 in).

Although we found relatively low non-target captures, the birds were all captured on uncovered floats suggesting some vulnerability to these floating sets. In addition to float sets, cameras were placed at each float set to evaluate behaviors of muskrats and non-target species as they encounter float sets. Cameras captured 9,356 encounters with float sets from 311,377 one minute video recordings. We found that cover type did not influence encounter rates of water birds at float sets. Water birds in general were 7.5 times more likely to encounter a float in the spring as compared to the fall. When examining behaviors at the floats, we found non-duck water birds were 10.1 times more likely to contact float sets as compared to puddle and diving ducks.

Regardless of guild, birds were 2.3 times less likely to contact a float set with a 1 in x1 in cover as compared to an uncovered float set, suggesting covers with smaller mesh sizes may be less attractive to birds. We captured 490 muskrats over 4,245 trap nights (0.115 muskrat per trap night) during fall and spring trapping season at all study locations over the two year study period. We evaluated 1,149 muskrat encounters with float sets over the two year study period from the video collected by trail cameras at each float set. Muskrats had a daily encounter rate of 0.27 encounters per day. Most muskrats would simply swim by the float without contacting it in any way (45.3%). Muskrats would also contact float by bumping the sides (14.6%) or climb onto the float which may or may not have resulted in getting trapped (40.1%). We found that there was no influence from a 1x1 or 6x6 cover type on whether a muskrat contacted or went on top/was trapped at a float set.

Further, we found that the use of covered float sets did not negatively impact trapping efficiency. In fact, larger mesh size (6 in x 6 in) showed a slight increase in efficiency compared to an uncovered float set. Further research is needed on different designs of float sets to better understand the impact on muskrat trapping efficiency and non-target incidental take.

Project Collaborators

R. J. Gross - M.S. Student, UND Biology/ ND Game and Fish Technician
Stephanie Tucker - ND Game and Fish Furbearer Biologist