Visitation Patterns and Behavior of Nearctic River Otters (Lontra canadensis) at Latrines Sadie S. Stevens1 and Thomas L. Serfass1,* Abstract - Little is known about the visitation patterns of Lontra canadensis (Nearctic river otter) at latrines. We used remote camera and video camera systems manufactured by TrailMaster® to determine when Lontra canadensis (river otters) occupying riverine habitats in Pennsylvania and Maryland visit latrines, what the group composition is during visits, and if either variable changes by season. We documented 173 visits to latrines by river otters. The majority of visits (102) were by single river otters. One hundred fifty of the total visits occurred at night. Most (111) lasted <1 min. The largest peak in visitation to latrines occurred immediately prior to and during the breeding season (February/March). Introduction Although many studies have documented movement patterns of Lontra canadensis Schreber (Nearctic river otter) (e.g., Bowyer et al. 1995, Erickson and McCullough 1987, Johnson and Berkley 1999, Reid et al. 1994, Route 1988), little has been done to determine the behavior of the species on a smaller scale, such as at latrines (Beckel 1982, Melquist et al. 2003). Such information provides valuable insight into the natural history of the species, and may improve the efficiency of population monitoring methods. Evaluating the behavior of river otters or other species at a specific portion of their home range is often best accomplished through observational studies. However, because of the river otter’s elusive nature, making enough observations to enable meaningful conclusions can be a challenge. Latrines, activity centers where river otters have been reported to defecate, loaf, and feed (Greer 1955, Liers 1951, Mowbray et al. 1976), are regularly used by the species (Greer 1955, Melquist and Hornocker 1983) and are the most obvious sign of its activity (Mowbray et al. 1976). Latrines often are characterized by a fishy odor (Poole 1954), are littered with river otter scats (Mowbray et al. 1976, Poole 1954), and generally are close to the water’s edge (Carpenter 2001, Greer 1955, and Mills 2004) in association with conifers, points of land, rock formations, beaver activity, fallen logs, dense canopy cover, tributary steams, and backwaters (Carpenter 2001, Greer 1955, Melquist and Hornocker 1983, Swimley 1996, Swimley et al. 1998). The exact purpose of latrines is unknown, although researchers have speculated that river otters use scent marking to advertise their presence and thereby minimize unwanted intraspecific contact (Melquist and Hornocker 1983, Melquist et al. 2003). Carpenter (2001) and Mills (2004) reported that the frequency of marking by river otters at latrines in Pennsylvania changes seasonally, and suggested a link between increased marking and the breeding season. 2008 NORTHEASTERN NATURALIST 15(1):1–12 1Frostburg State University Biology Department, 101 Braddock Road, Frostburg, MD 21532. *Corresponding author - tserfass@frostburg.edu. 2 Northeastern Naturalist Vol. 15, No. 1 We used remote photography and videography to document the visitation patterns and behavior of river otters at 11 latrines in Pennsylvania and Maryland from October 2002 to July 2004. We evaluated group composition during visits to latrines, as well as the time and length of the visits, to determine if any of the associated values changed seasonally. To our knowledge, this is the first use of remote cameras to monitor the behavior of free-ranging river otters. Methods Study area Our study was conducted along the Youghiogheny River in Fayette County, PA, and Garrett County, MD, and along Tionesta Creek in Forest County, PA. River otters were reintroduced to both waterways beginning in the 1990s and have become established (Carpenter 2001, Serfass et al. 1993, US Department of Agriculture Forest Service 2002). Mills (2004) determined through monthly surveys for scats that all 3 study sites were occupied by river otters. Active latrines (areas where fresh river otter scat often was detected during monthly surveys) occurred throughout the study sites (Mills 2004). We chose latrines based on regular occurrence of river otter sign, accessibility, and ease of camera placement. Sites considered ideal were those readily accessible for us to place and monitor the camera systems, but unlikely to be frequently visited by the general public. The Youghiogheny River flows from Preston County, WV, through Garrett County, MD, to Somerset, Fayette, Westmoreland, and Allegheny counties of Pennsylvania (US Department of the Interior 1978). One hundred and five species of fish occur in the river drainage (Hendricks 1980). The Youghiogheny River is a 6th-order stream. Within the study area, deep pools and large boulders are abundant and often associated with latrines. Sections of the Youghiogheny, including our study area in Pennsylvania, are among the most heavily used whitewater in the eastern United States (US Department of the Interior 1978). Our study site along the Youghiogheny River in Fayette County, PA is within the boundaries of Ohiopyle State Park. The section of river is paralleled by a regularly used bike trail, on which motorized vehicles are prohibited. Our study site along the Youghiogheny River in Garrett County, MD is located on posted private land. Tionesta Creek flows approximately 70 km through a section of the Allegheny National Forest in Forest County, PA. Tionesta Creek is a 6th-order stream that is of lower gradient than the Youghiogheny, with numerous backwaters, undercut banks, and occasional large boulders (Swimley 1996). Allegheny National Forest land is interspersed with private holdings. The majority of dwellings on the private land are seasonal, although the area attracts visitors for recreation throughout the year (Swimley 1996). Tionesta Creek is paralleled by a road on one side and a trail on the other. The trail is not heavily used, although it does provide access for hikers, hunters, fishermen, and ATV riders. Cameras were placed on the side of the creek 2008 S.S. Stevens and T.L. Serfass 3 paralleled by the trail because it contained more active latrines and the more limited access allayed our concerns about theft. Camera placement and procedures We placed video cameras along the Youghiogheny River in Pennsylvania and 35-mm cameras along both the Youghiogheny River and Tionesta Creek at regularly used latrines from October 2002 to July 2004. Both camera systems were controlled by Trailmaster® infrared monitors (Goodson and Associates, Lenexa, KS). We used active (TM1500 and TM1550) and passive (TM500 and TM550) 35-mm camera systems and passive video camera systems (TM700V). Latrines known to be active were chosen based on the results of surveys conducted immediately prior to this study (see Mills 2004). Camera systems were consistently maintained at 11 latrines. Whenever an animal visited a latrine, properly functioning Trailmaster monitors recorded the date and time and signaled the attached camera to take a photograph or video. We placed cameras approximately 2.5–4 m from the center of the latrine, often mounting them in trees to provide an aerial view of the area. The entire latrine area was always visible through the camera’s or video camera’s viewfinder (see Stevens 2005). We visited camera sites from twice a week to once every 2 weeks, depending on location, accessibility, and how quickly film typically was expended (based on experience gained during initial phases of the project). At each visit to a camera site, we changed batteries and film if needed, checked the status of the camera and monitor (e.g., number of photographs left, condition of batteries, and number of events recorded), and recorded any problems with the system. Film and data were not collected at every visit. The mean number of days between changes was 21 for film and 11 for video. When film and video were collected, we also recorded the number of days the camera system had been functional. The date and time at which the monitor or camera stopped being fully functional could be determined from the data in the monitor and the resulting photos or videos, which also were time- and date-stamped. Common causes of loss of functionality between camera checks included failure of flash or video camera light (time of this occurrence could be determined from resulting photos or videos) or depletion of monitor’s data storage capacity (date and time of such an event could be determined from the monitor). We considered a system functional for a day only if it was fully functional for the entire 24-hr period. If, for example, the camera’s flash or the video camera’s light did not work, rendering photos taken at night indiscernible, the system was considered nonfunctional for that day. While at the camera site, we also checked for the scat or tracks of river otters left since our last visit. We reviewed film and videotape after each “camera check” to determine when river otters were visiting latrines and how many river otters were present during each visit. We classified the season during which each visit to a latrine by a river otter(s) occurred according to the Gregorian (standard) calendar, and also classified each visit as occurring during day, night, dawn, 4 Northeastern Naturalist Vol. 15, No. 1 or dusk. Dawn and dusk were defined as the periods when the sun was <6° above or below the horizon, and were calculated for each study area separately to compensate for differences in latitude. We also recorded the amount of time river otters spent at the latrine during each visit. Length of visit was recorded in 1-min intervals (e.g., any visit lasting 60 sec or less was recorded as 1 min and any visit lasting 61 to 120 sec was recorded as 2 min) to maintain consistency between still cameras (which were set to take a photograph every min when motion was detected) and video cameras (which filmed the entire time motion was being detected). If >30 min passed between 1 photograph and the next or the end of 1 video segment and the beginning of the next, we classified the 2 photographs or videos as separate visits. Therefore, if 1 photograph of a river otter was taken at 4:15 and another at 4:46, the 2 events would have been recorded as separate visits. Data analysis Data were analyzed using Minitab (Minitab Inc., State College, PA). We used chi-square analysis (Zar 1999) to determine if group composition or time of visits was different among different months, seasons, or study sites. Chi-square analysis also was used to determine if the number of detections (in total and by study site) varied by season based on the number of functional camera days per season. Kruskal-Wallis (Zar 1999) was used to determine if the length of visitation changed seasonally or by time of day. Results Camera systems were deployed for a total of 5052 camera-days (video cameras for 1892 camera-days at 4 latrines; still cameras for 3160 cameradays at 6 latrines), and were functional for 55% of that time (video cameras for 891 days; still cameras for 1909 days). Camera systems detected 173 visits to latrines by river otters. Eighty-four visits were captured on film and 89 on video. Thirty-three visits were photographed at 1 latrine (SR1) along the Youghiogheny River in Garrett County, MD; 49 were photographed at 5 latrines (TC3, TC5, TC10, TC28, TC3B7) along Tionesta Creek in Forest County, PA (range = 2–30); and 2 were photographed at 1 latrine (YR10) along Youghiogheny River in Fayette County, PA. One latrine resulted in no photographs of river otters, although scat had been previously observed at the site. Eighty-nine visits were videotaped at 4 latrines (YR5, YR6, YR10, YR12) along the Youghiogheny River in Fayette County, PA (range = 2–58). The majority of the total number of visits (86.1%) was recorded at 4 latrines: 2 along the Youghiogheny River in Fayette County, PA (YR5 [33.5%] and YR6 [16.1%]); 1 along the Youghiogheny River in Garrett County, MD (SR1 [19.1%]); and 1 along Tionesta Creek (TC3 [17.3%]) (Fig. 1). The 2 latrines along the Youghiogheny River in Fayette County, PA at which river otters were most frequently detected (YR5 and YR6) were 3.3 km apart. At least 1 camera system at each study site (i.e., the Youghiogheny River in Maryland, the Youghiogheny River in Pennsylvania, and Tionesta Creek) recorded a 2008 S.S. Stevens and T.L. Serfass 5 visit by river otters during months in which >10 visits to latrines by river otters were detected (Fig. 2). Figure 1. The number of visits by river otters that were detected at 10 latrines along the Youghiogheny River in Fayette County in southwestern Pennsylvania and Garrett County in Maryland, and along Tionesta Creek in Forest County in northwestern Pennsylvania from October 2002 to July 2004. Latrines are grouped by study site. Figure 2. The number of visits to 10 latrines by river otters along the Youghiogheny River in Fayette County in southwestern Pennsylvania and Garrett County in Maryland, and along Tionesta Creek in Forest County in northwestern Pennsylvania by month from October 2002 to July 2004. 6 Northeastern Naturalist Vol. 15, No. 1 We recorded the presence of fresh scat and/or tracks during 139 camera checks. However, only 51 (36.7%) of those camera checks resulted in our obtaining a photograph or video of a visit to a latrine by a river otter. Therefore, camera systems did not detect every visit to a latrine by a river otter(s). There were occasions when the monitor or camera was out of film or batteries, was damaged, or for unknown reasons did not detect the presence of a river otter or group of river otters. Based on the presence of tracks and scat, camera systems did not record at least 11 visits to latrines by river otters in the summer, 39 in the fall, 20 in the winter, and 18 in the spring. However, more than the known number of visits may have been missed because river otters did not always deposit scat or leave tracks at a latrine, as evidenced on 24 occasions when we obtained a photograph or video of a river otter during a camera check, but no fresh scat or tracks were present. Seasonal and monthly visitation patterns The frequency of visits detected by our cameras changed throughout the year. We documented 100 visits to latrines in winter, 37 in fall, 33 in spring, and 3 in summer. A peak in the number of detections occurred in February and March (Fig. 2). The number of detections per functional camera day differed significantly among seasons (P ≤ 0.001; 0.045 detections per functional camera day in spring, 0.008 in summer, 0.047 in fall, and 0.114 in winter) and months (P ≤ 0.001) (Fig. 3). The greatest deviation from expected values occurred during summer (mainly June) and winter (mainly February and March). During summer, cameras recorded fewer visits per functional camera day than expected, and during winter they recorded more than expected. Figure 3. The number of visits to 10 latrines by river otters that were detected along the Youghiogheny River in Fayette County in southwestern Pennsylvania and Garrett County in Maryland, and along Tionesta Creek in Forest County in northwestern Pennsylvania per functional camera day by month from October 2002 to July 2004. 2008 S.S. Stevens and T.L. Serfass 7 Daily visitation patterns One-hundred and fifty detections (87.2%) of river otters occurred during night. Peaks in detection occurred from 100–200, 400–500, and 2100–2300. When dawn, day, and dusk were combined and compared to night, we were able to determine that time of day of visit did not differ between study sites. (Comparisons of visitation time among study sites could not be made without combining dawn, day, and dusk due to expected chi-square counts <1.0 for some categories; Zar 1999.) This nocturnal pattern also was consistent among seasons, and ranged from a low of 82% to a high of 100%. When spring, summer, and fall were combined and compared to night, we were able to determine that there was no significant difference in visitation times between winter and all other seasons combined. (Again, some categories had to be combined to prevent chi-square expected counts of <1.0 for some categories; Zar 1999.) Eleven of the 12 visits detected along the Youghiogheny River in Fayette County, PA during dawn, day, and dusk were recorded at 1 latrine (YR5). All 6 visits detected along the Youghiogheny River in Garrett County, MD during dawn, day, and dusk were recorded at 1 latrine (SR1), as were all 5 visits detected along Tionesta Creek (all recorded at TC5). Group composition We could estimate the number of river otters present during 172 of the 173 detections of river otters at latrines. Of those visits, 102 (59.3%) were by single river otters, 33 (19.2%) by 2 otters, 30 (17.4%) by 3 otters, and 7 (4.1%) by 4 otters. Group composition during visits did not differ signifi- cantly among study sites. Most visits, regardless of group size or study site, took place at night. Eighty-four of the 102 visits by 1 otter, 28 of the 33 visits involving 2 otters, and 36 of the 37 visits involving >2 otters occurred at night. Single river otters were detected at latrines more often during dawn, day, and dusk than were groups of ≥2 (P = 0.047). (For analyses, night was compared with all other times of day combined to alleviate the problems caused by low expected chi-square approximations; visits to latrines by single river otters also were compared to visits involving ≥2 river otters to eliminate expected chi-square counts of <1.) River otter group size during latrine visits differed among seasons (P = 0.012). During spring, there were fewer visits by ≥2 river otters and more visits by single river otters than expected based on chi-square approximations. The deviation was more pronounced, with more frequent visits by single otters, when comparing the breeding season (March and April) to all other months combined (P ≤ 0.001). When comparing group size of river otters visiting latrines in October through January with the rest of the year, we were able to determine that during those months there were more visits by groups of ≥2 otters than expected based on chi-square approximations (P ≤ 0.001). Length of visit Of the 173 total visits to latrines by river otters, 111 lasted <1 min; only 6 lasted >10 min. The longest documented visit lasted 35 min and involved 8 Northeastern Naturalist Vol. 15, No. 1 3 river otters. Length of visit did not differ significantly among months, seasons, or times of day. When ≥2 river otters were present, however, visits lasted significantly longer (median = 2 min) than when only 1 river otter was present (median = 1 min) (P ≤ 0.001). Discussion Remote cameras were an effective means for gathering data on the visitation patterns of river otters at latrines in riverine systems. By visually searching for otter sign during regular visits to latrines, we were able to determine that camera systems missed visits by river otters at relatively equal rates (missed events to detections) among seasons. Seasonal and monthly visitation patterns River otters visited the latrines monitored during our study more frequently in winter (as defined by the Gregorian calendar) than other seasons. Frequency of visitation during winter was 3 times that during either spring or fall. We seldom detected river otters at latrines in summer. Peaks in visitation to latrines by river otters occurred in February/March and October/ November. The results of our study are similar to those of Carpenter (2001) and Mills (2004), who reported that scat marking for river otters in Pennsylvania and Maryland is seasonal with peaks in March and October/November. (Note: The majority of March, which Carpenter [2001] and Mills [2004] refer to as spring, is classified as winter by the Gregorian calendar, which we used in this study.) The peak in latrine visitation and marking observed in February/March is likely related to the breeding season. From research in nearby areas (Maryland [Mowbray et al. 1979] and New York [Hamilton and Eadie 1964]), we presume that river otters in our study areas breed in March and April. If this is correct, the February/March peak in latrine visitation and marking (Carpenter 2001, Mills 2004) occurs just before and during the breeding season, when river otters are searching for mates. We also documented more visits to latrines by single river otters during the breeding season than during other parts of the year, which suggests that river otters visiting latrines in February and March may be engaged in the solitary activity of searching for a mate. The peaks in latrine visitation and marking (Carpenter 2001, Mills 2004) observed in October/November, as well as the increase in visits by groups of otters from October through January, likely are a result of the increased movement of females with offspring. River otters in Pennsylvania and Maryland likely give birth in March or April (based on Hamilton and Eadie’s [1964] reports about New York river otters, which occur at similar latitude). River otters might not swim and dive in deep water until 165 days of age (Melquist et al. 2003), and female river otters remain near the natal den after birth (Melquist and Hornocker 1983). Therefore, family groups likely do not travel far until October, when latrine visitation and marking (Carpenter 2001, Mills 2004) also increase. Young river otters begin to disperse before 2008 S.S. Stevens and T.L. Serfass 9 the breeding season (Melquist and Hornocker 1983), and at that time visitation to latrines by groups of otters also decreases. During the breeding season, when encountering other sexually mature river otters becomes critical, visitation to latrines and marking (Carpenter 2001, Mills 2004) increase. The peak in visitation to latrines by river otters that we documented immediately preceding and during the breeding season, coupled with Carpenter’s (2001) and Mills’ (2004) reports of increased marking during the same time period, suggests that during the breeding season, river otters mark to advertise their presence. Daily visitation patterns River otters in each of our study areas were more frequently detected visiting latrines at night. Although our data suggest that groups visited latrines even less often during dawn, day, and dusk than single river otters, this may be a function of small sample size. Latrine visitation patterns of river otters are likely a reflection of activity patterns, which are known to be inconsistent throughout the species’ range and even throughout the year in any particular region (Melquist and Hornocker 1983). For example, Melquist and Hornocker (1979) reported no significant difference between nocturnal and diurnal activity of river otters in Idaho, although visual sightings were made most often during dawn and dusk. Mack (1985) also determined that river otters in Colorado were active both day and night. Liers (1951) noted that river otters in the wild travel mostly at night. Griess (1987) and McDonald (1989) also reported that river otters in Tennessee and Ohio, respectively, were most active at night. Melquist and Hornocker (1983) reported that river otters became more diurnal during winter. We did not find a difference between daily visitation patterns when comparing winter to other seasons. Several factors influence the activity patterns of a species and individuals within a species. Studies of Vulpes vulpes Linnaeus (red fox), Canis latrans Say (coyote), Lynx rufus Schreber (bobcat), Panthera pardus fusca Meyer (leopard), Asio flammeus Pontoppidan (Short-eared Owl), Mustela vison Schreber (mink), and Crotalus atrox Baird and Girard (Western Diamondbacked Rattlesnake) and Micrurus fulvius Linnaeus (Northern Coral Snake) have shown that activity patterns of predators are influenced by those of their prey (Ables 1969, Bider 1962, Gerell 1969, Reynolds and Gorman 1999, Santiapillai et al. 1982). Fish, the main food source for river otters, is available at any time and likely exerts little influence on activity patterns. The river otter’s high basal metabolic rate (McNab 2002), however, may make meeting daily energy requirements impossible when restricting activity to only specific portions of the day (Spinola 2003). Activity patterns of animals are affected not only by the activity patterns of their prey, but also by the activity patterns of their major predators (Melquist et al. 1980), of which the river otter has few (Drummer 1954). Van Shaik and Griffiths (1996) reported that a surprising number of carnivorans are cathemeral, presumably because of such low risks of predation. Such a hypothesis may help explain the difference in the diel cycle of the river otter 10 Northeastern Naturalist Vol. 15, No. 1 from region to region, and the variation in the time of day river otters visited latrines in our study area. Humans may be the biggest threat to river otter survival, and several researchers (Caras 1967, Fuller and Deems 1979, Melquist and Hornocker 1983) have suggested that close proximity to humans causes the river otter to be more nocturnal. We selected study sites with minimal human activity; however, some disturbance in the form of roads and trails was necessary due to the size and weight of some camera equipment. This disturbance may have had some influence on the latrine visitation patterns of river otters. Acknowledgments This project was made possible by a US Fish and Wildlife Service State Wildlife Grant (administered by the Pennsylvania Game Commission [PGC]) and the Pennsylvania Wild Resource Conservation Fund [PWRCF]. The US Department of Agriculture Allegheny National Forest (ANF) also provided funding and logistical support. A. Hayden (deceased) and J. Hassinger of the PGC, F. Felbaum and R. Stanley of the PWRCF, and B. Nelson of the ANF have continually supported river otter research in Pennsylvania. Literature Cited Ables, E.D. 1969. Activity studies of red foxes in southern Wisconsin. Journal of Wildlife Management 33:145–153. Beckel, A.L. 1982. Behavior of free-ranging and captive river otters in north-central Wisconsin. Ph.D. Dissertation. University of Minnesota, Minneapolis, MN. Bider, J.R. 1962. Dynamics and the temporo-spatial relations of a vertebrate community. Ecology 43:634–646. Bowyer, R.T., J.W. Testa, and J.B. Faro. 1995. Habitat selection and home ranges of river otters in a marine environment: Effects of the Exxon Valdez oil spill. Journal of Mammalogy 76:1–11. Caras, R.A. 1967. Freshwater Clown: The River Otter. North American Mammals. Galahad Books, New York, NY. Carpenter, C.P. 2001. Scat marking and the use of latrine sites by river otters along Tionesta Creek, northwestern Pennsylvania. M.Sc. Thesis. Frostburg State University, Frostburg, MD. Drummer, F. 1954. The Animal Kingdom. Vol. 2. Greystone Press, New York, NY. Erickson, D.W., and C.R. McCullough. 1987. Fates of translocated river otters in Missouri. Wildlife Society Bulletin 15:511–517. Fuller, K., and E. Deems. 1979. Maryland’s river otter. Maryland Conservationist May/June:5–6. Gerell, R. 1969. Activity patterns of the mink in southern Sweden. Oikos 20: 451–460. Greer, K.E. 1955. Yearly food habits of the river otter in the Thompson Lakes Region, Northwestern Montana, as indicated by scat analyses. American Midland Naturalist 54:299–313. Griess, J.M. 1987. River otter reintroduction in Great Smoky Mountains National Park. M.Sc. Thesis. University of Tennessee, Knoxville, TN. Hamilton, W.J., Jr., and W.R. Eadie. 1964. Reproduction in the otter, Lutra canadensis. Journal of Mammalogy 45:242–252. 2008 S.S. Stevens and T.L. Serfass 11 Hendricks, M.L. 1980. The distribution of fishes of the Youghiogheny River. M.Sc. Thesis. Frostburg State University, Frostburg, MD. Johnson, S.A., and K.A. Berkley. 1999. Restoring river otters in Indiana. Wildlife Society Bulletin 27:419–427. Liers, E.E. 1951. Notes on the river otter (Lutra canadensis). Journal of Mammalogy 39:438–439. Mack, C.M. 1985. River otter restoration in Grand County, Colorado. M.Sc. Thesis. Colorado State University, Fort Collins, CO. McDonald, K.P. 1989. Survival, home range, movements, habitat use, and feeding habits of reintroduced river otters in Ohio. M.Sc. Thesis. The Ohio State University, Columbus, OH. McNab, B.K. 2002. The Physiological Ecology of Vertebrates: A View from Energetics. Cornell University Press, Ithaca, NY. Melquist, W.E., and M.G. Hornocker. 1979. Methods and techniques for studying and censusing river otter populations. Forest, Wildlife, and Range Experiment Station, University of Idaho, Moscow, ID. Technical Report 8. Melquist, W.E., and M.G. Hornocker. 1983. Ecology of river otters in west-central Idaho. Wildlife Monographs 83. Melquist, W.E., J.S. Whitman, and M.G. Hornocker. 1980. Resource partitioning and coexistence of sympatric mink and river otter populations. Proceedings of the Worldwide Furbearer Conference 1:187–220. Melquist, W.E., P.J. Polechla, and D. Toweill. 2003. River otter (Lontra canadensis). Pp. 708–734, In G.A. Feldhamer, B.C. Thompson, and J.A. Chapman (Eds.). Wild Mammals of North America: Biology, Management, and Conservation. 2nd Edition. Johns Hopkins University Press, Baltimore, MD. Mills, M.A. 2004. Scat-marking by river otters in Pennsylvania and Maryland. M.Sc. Thesis. Frostburg State University, Frostburg, MD. Mowbray, E.E., Jr., J.A. Chapman, and J.R. Goldsberry. 1976. Preliminary observations on otter distribution and habitat preferences in Maryland with descriptions of otter field sign. 33rd Northeast Fish and Wildlife Conference, Hershey, PA. Mowbray, E.E., D. Pursely, and J.A. Chapman. 1979. The status, population characteristics, and harvest of the river otter in Maryland. Publications in Wildlife Ecology No. 2. Maryland Wildlife Administration, Maryland Department of Natural Resources, Annapolis, MD. Poole, E.L. 1954. The otter: Pennsylvania’s rarest furbearer. Pennsylvania Game News 25:4–9. Reid, D.G., T.E. Code, A.C.H. Reid, and S.M. Herrero. 1994. Spacing, movements, and habitat selection of the river otter in boreal Alberta. Canadian Journal of Zoology 72:1314–1324. Reynolds, P., and M.L. Gorman. 1999. The timing of hunting in Short-eared Owls (Asio flammeus) in relation to the activity patterns of Orkney voles (Microtus arvalis orcadensis). Journal of Zoology 247:371–379. Route, W.T. 1988. Distribution and abundance of river otter in Voyageurs National Park, Minnesota. M.Sc. Thesis. Michigan Technical University, Houghton, MI. Santiapillai, C., M.R. Chambers, and N. Ishwaran. 1982. The leopard Panthera pardus fusca (Meyer 1974) in the Ruhuna National Park, Sri Lanka, and observations relevant to its conservation. Biological Conservation 23:5–14. Serfass, T.L., R.P. Brooks, and L.M. Rymon. 1993. Evidence of long-term survival and reproduction by translocated river otters, Lutra canadensis. Canadian Field- Naturalist 107:59–63. 12 Northeastern Naturalist Vol. 15, No. 1 Spinola, R.M. 2003. Spatio-temporal ecology of river otters translocated to western New York. Ph.D Dissertation. The Pennsylvania State University, University Park, PA. Stevens, S.S. 2005. Visitation patterns and behavior of river otters at latrines in Pennsylvania and Maryland. M.Sc. Thesis. Frostburg State University, Frostburg, MD. Swimley, T.J. 1996. Predicting river otter marking sites in Pennsylvania. M.Sc. Thesis. The Pennsylvania State University, University Park, PA. Swimley, T.J., T.L. Serfass, R.P. Brooks, and W.M. Tzilkowski. 1998. Predicting river otter latrine sites in Pennsylvania. Wildlife Society Bulletin 26:836–845. US Department of Agriculture Forest Service. 2002. Allegheny overview. Allegheny National Forest, Warren, PA. US Department of the Interior. 1978. Youghiogheny River: A wild and scenic rivers study Maryland-Pennsylvania. Heritage Conservation and Recreation Service Northeast Regional Office, Philadelphia, PA. van Shaik, C.P., and M. Griffiths. 1996. Activity periods of Indonesian rain forest mammals. Biotropica 28:105–112. Zar, J.H. 1999. Biostatistical Analysis. Prentice Hall, Upper Saddle River, NJ.