Occasional Papers Museum of Texas Tech University Number 226 23 September 2003 Home Range and Movement of Nutria (Myocastor coypus) at Spring Lake in Central Texas, with Anecdotal Comments on the American Beaver (Castor canadensis) of the Same Area W. R. Melissa McCvlleyDenena, Richard Manning, and Thomas Simpson Home range is the confined area in which ani¬ duced to other parts of North America in large num¬ mals carry out their daily activities. This area is lim¬ bers to consume undesirable aquatic vegetation in the ited by the structure of surrounding habitat, competi¬ late 1930’s (Willner, 1982). Today, this exotic pest tion and territoriality with conspecific animals, and the can be found nationwide in 15 states and continues to distribution of food and cover (Litvaitis et aL, 1996). expand its distribution (Bounds et al., 2001). Nutria Radio telemetry and mark and recapture techniques generally weigh around 5.4 kg. After one year, fe¬ are methods commonly used for measuring an males reach sexual maturity and begin breeding. Ges¬ individual’s home range. Radio telemetry techniques, tation periods average 130 days, and litter size is ca. first used in the 1960s (Cochran and Lord, 1963), re¬ five. Nutria are sedentary and tend to remain in one sult in higher accuracy due to the freedom of research¬ location throughout their life (Adams, 1956). ers to locate a radio marked animal when desired. Nutria compete with native wildlife species for A number of studies have been conducted using food and space. The muskrat is being displaced by radio telemetry to estimate the home range of mam¬ nutria, and waterfowl and migratory birds are losing mals, reptiles, amphibians, and birds. At Spring Lake, valuable food and cover resources as a result of in¬ two other studies using radio telemetry techniques were creased nutria populations (Bounds, 2000). The feed¬ completed. Aguirre (1999) studied space use patterns ing habits of nutria also are destructive to sensitive of the common snapping turtle (Chelydra serpentina wetland ecosystems. The food habits of nutria have serpentina). Hudson (1999) radio tracked raccoons been studied more extensively than their home range. (Procyon lotor) to estimate their home range. Many of these studies have been conducted in Louisi¬ ana (Wilsey and Chabreck, 1991, Nyman et al., 1993, Nutria (Myocastor coypus), semi-aquatic rodents, Taylor and Grace, 1995). Simpson (1980) and Swank first were introduced in California for the fur trade in and Petrides (1954) studied the food habits of nutria in 1899 (Evans, 1970). They subsequently were intro¬ Texas. Towns (2002) evaluated stomach contents of 2 Occasional Papers, Museum of Texas Tech University nutria at Spring Lake, Hays County, Texas. Diet var¬ information gained from their radio telemetry study ies throughout the year and contains grasses, roots, (Bounds et ah, 2001). Studies also have been carried stems, and leaves (Willner, 1982)* Nutria dig up an out on the movement of nutria using mark and recap¬ entire plant to eat a single root (Bounds et al., 2001). ture methods (Adams, 1956, Robicheaux, 1978, Not only does this destroy the plant, but also it causes Ryszkowski, 1966), In 1997, the distribution of nu¬ soil erosion. tria in their native habitats in Argentina was evaluated (Guichon and Cassini, 1999). Coreil and Perry (1977) noted that it was diffi¬ cult to radio collar nutria due to skin sensitivity to some In our study, radio telemetry was used to calcu¬ collars but were able to successfully collar seven adults. late the home range of nutria living in a unique spring- Home range and movement of nutria using radio te¬ river system. From this study, movement and behav¬ lemetry have since been studied in Mississippi ior of the rodents were analyzed. The information (Lohmeier, 1981), Louisiana (Coreil, 1984), and Mary¬ gathered maybe useful in management strategies when land (Ras, 1999). In 2001, a three-year pilot study attempting to control nutria populations. A widely rec¬ began in Maryland. The goal of this project is the ognized and successful method for controlling the successful eradication of nutria in Maryland with the growing nutria populations has not yet been accepted. Materials and Methods Study Site the shore immediately surrounding this area is cov¬ ered with concrete and buildings. The southern part Spring Lake is located within the city limits of of the main lake ends in two spillways which empty San Marcos, Hays County, Texas. Spring Lake is ap¬ into the San Marcos River. The eastern section of proximately an 8 ha reservoir that is fed by an esti¬ Spring Lake, the slough, is fed by the Sink Creek Wa¬ mated 200 springs arising from the Edwards Aquifer. tershed. This area is distinctly more stagnant than the The lake is dammed 460 meters downstream from the main lake and receives minimal water flow. A golf headwaters (Brune, 1981). Water temperature at course and softball fields border this backwater re¬ Spring Lake remains fairly constant at 21 ± 3 °C due gion. to these springs (Groeger et al., 1997). The ecosys¬ tem present at this site is highly productive because of Hydrilla (Hydrilla verticillata), a highly invasive the constant temperature, constant water flow, and species, was found submersed throughout the lake. high water quality (Seaman ,1997). Dense beds of the introduced elephant ears (Colocasia esculenta) lined a large portion of the main lake’s shore. In 1946, Spring Lake was established as a theme During spring and summer, dense mats of algae and park with glass-bottom boats and an underwater sub¬ macrophytes, including hydrilla, delta arrowhead marine theatre (Coley, 2000), In 1994, Southwest (Sagiitaria platyphylla), water hyacinth (Eichhornia Texas State University acquired Spring Lake and be¬ crassipes), floating fem (Ceratopteris thalictroides), gan converting the property from a theme park into a water lettuce (Pistia stratiotes), Brazilian parrot’s restored wetland dedicated to conservation, education, feather (Myriophyllum brasiliensis), and lotus (Nuphar and research (Williamson, 2001). luted) covered most of the surface of the slough and the southern part of the main lake. Plant species grow¬ Spring Lake is located on the Balcones Escarp¬ ing on the banks of Spring Lake included bald cypress ment Fault Zone, which is bordered to the west by the (Taxodium distichum), American elm (Ulmus Edwards Plateau Region and to the east by the Black- americand), hackberry (Celtis spp.), black willow land Prairie Region. The lake is separated into two (Salix nigra), box elder (Acer negundo), Japanese sections: the main lake and the slough. Natural springs honeysuckle (Lonicera japonic a), poison ivy (Toxico¬ arise in the northern part of the main lake. Much of dendron radicans), and cattail (Typha latifolia). 3 Denena et al.—Home Range and Movement of Nutria (Myocastor coypus) During this study, a boardwalk was built over A modified Lincoln-Peterson Index was used to the slough along the northwest bank by the Southwest calculate a population estimate (N) of the nutria living Texas State University Biology Department, Texas in Spring Lake (Nichols and Conroy, 1996). Trapping Parks and Wildlife Department, and U.S. Fish and Wild¬ data from two consecutive nights were used. life Service. Construction began on 20 February, 2001 and was completed 6 December, 2001. The board¬ Radio Telemetry Techniques walk was opened to the public to promote wetland education. Reconstruction of the Spring Lake dam Radio collars (Wildlife Materials, Inc,, LPM- began 11 May, 2001, and continued until the end of 2190M) placed around the nutria’s neck consisted of our study. a waterproof transmitter mounted to an adjustable leather strap. The transmitters emitted a signal on the Capture and Marking Techniques 151 MHz band. Data were collected from canoe or by foot, using a three-element collapsible Yagi antenna and Small (81x25x31 cm) Tomahawk live traps a portable receiver (Wildlife Materials, Inc., TRX- (Tomahawk Live Trap Company, Model #108) were 100OS). Once a location was determined, it was plot¬ set along the shores of Spring Lake in 25 different ted on a base map. Time, air temperature, and behav¬ locations from 13 February, 2001, through 7 Novem¬ iors observed at the location were also recorded. ber, 2001. Trapping occurred on 43 nights for a total of 335 trap nights. The traps were set during late Radio telemetry data were collected from the time afternoon at the water’s edge near a burrow or in ar¬ the first animal was collared, 15 February, 2001, until eas where signs of nutria activity could be seen. Traps 7 November, 2001; when no signals were transmitted were checked the following morning. Traps were and the last collar was retrieved. The nutria’s activity baited with carrots and sweet potatoes. In Louisiana, period (crepuscular and nocturnal) was designated as Ragan (1960) set up nutria feeding stations to test the 1900 hour through 700 hour. This 12-hour span was preferred bait of nutria; carrots were taken by feral divided into six observation periods of two hours du¬ nutria 87.2 percent of the time and sweet potatoes ration so that samples were taken throughout the ac¬ were taken 94.3 percent of the time. tivity period. Two locations per week on all collared individuals were recorded during randomly chosen Once trapped, nutria were sedated by injecting a observation periods. Each observation period was combination of ketamine HC1 (ketaset), a dissociative sampled equally. Locations were recorded periodi¬ anesthetic, and xylazine HC1 (rompun), an analgesic cally at other times to find burrow or nesting bed loca¬ sedative, with a two to one ratio, respectively (Bo et tions. al., 1994). Weight was measured to the nearest kilo¬ gram by placing a dog harness on the animal and using Global Positioning Systems (GPS) points at the a spring scale. Total length of body, length of tail, previously recorded locations were taken at Spring Lake length of hind foot, and ear length were recorded in using GPS ProMARK X CP (Magellan, Serial #3D millimeters. Weight and linear measurements were 000123) and a Multi-Path Resistant Antenna (Magellan, analyzed with a t-test in Microsoft Excel. Hind foot Model #39017). Magellan post-processing software length was used to estimate the age of the individual. (MSTAR, Version 2.06) then was used to perform dif¬ According to Adams (1956), an adult older than five ferential processing of the GPS points with GPS data months will have a hind foot length greater than 127 from the Continually Operating Reference Stations mm. Sex was determined by the presence or absence (CORS) in Austin, Texas. This improved the accu¬ of a baculum. Equal numbers of males and females racy of the points to within a few meters. were radio collared. Passive Integrative Transpon¬ ders (PIT) (AVID Microchips, 12 mm) were injected The data were imported into GIS software under the skin of the right thigh for future identifica¬ (ArcView, Version 3.2a) and used to create minimum tion. The animal was placed back into the trap, al¬ convex polygons to calculate home range area and lowed to recover, and released. maximum linear distance traveled for adult nutria 4 Occasional Papers, Museum of Texas Tech University (Ostro et at., 1999, Powell 2000), These polygons All field activity was conducted under the aegis then were overlaid onto a Digital Orthophoto (1997) of a scientific collecting permit issued by The Texas with one foot resolution. The Digital Orthophoto was Parks and Wildlife Department (permit number, SPR- provided by Capital Area Planning Council (CAPCO). 1192-569). The Institutional Animal Use and Care Com¬ Comparisons then were made between individuals and mittee permit number for this study was SWT-IACUC sexes with t-tests (alpha = 0.05) in Microsoft Excel. 2001-1. All voucher material is deposited in the mam¬ mal collection, Department of Biology, at Southwest Texas State University, San Marcos, Texas. Results Capture and Marking 382 mm and males averaged 3 71 mm. Hind foot length ranged from 130 mm to 150 mm; females averaged A total of 14 adult nutria (nine males and five 13 3 mm and males averaged 138 mm. Ear length ranged females) was collared and followed during this study. from 20 mm to 32 mm; females averaged 25 mm and Sex, weight, total length, length of tail, length of hind males averaged 24 mm. T-tests were performed to foot, ear length, and whether the nutria’s home range determine if there was a significant difference between was calculated are indicated in Table 1. Female N14 females and males regarding weight (d.f. = 12, t = was excluded from linear calculations because she was 1.91, P > 0.05), total length (d.f. = 12, t = 0.43, P > not considered to be an adult. 0.05), tail length (df. - 12, t - 0.33, P > 0.05), hind foot length (df. = 12, t = 1.27, P > 0.05), and ear The weight of collared individuals ranged from length (d.f = 12, t = 0.49, P > 0.05). No statistical 3.6 kg to 5.9 kg; females weighed an average of 4.4 significant difference was detected. kg and males weighed an average of 5.1 kg. Total length ranged from 660 mm to 960 mm; females aver¬ The population estimate of nutria found at Spring aged 839 mm and males averaged 859 mm. Tail length Lake using the modified Lincoln-Peterson Index at the ranged from 200 mm to 430 mm; females averaged beginning of the study, February, was 16 individuals. Table J. Radio collared nutria at Spring Lake, Hays County, Texas, in 2001. Key: M = male, F = females; weight in kilograms (kg), linear measurements in millimeters (mm), and X indicates home range was calculated. Inidividual Sex Weight Total Tail Length Hind Foot Ear Length Home Range number (kg) Length (mm) Length (mm) Calculated (mm) (mm) N3 M 5.9 960 430 150 29 X N4 F 4.5 880 360 140 27 X N5 F 4.5 910 410 135 28 X N6 F 5.0 890 430 140 27 X N7 F 3.6 795 350 130 20 X N8 M 4.5 855 425 138 20 N9 M 5.4 950 380 135 25 Nil M 5.7 910 400 135 20 X N12 M 4.5 820 360 130 20 X N13 M 5.0 880 380 140 20 N14 F 2.7 720 360 120 23 N15 M 4.5 860 370 140 32 N16 M 4.5 660 200 130 24 N17 M 5.4 840 395 145 25 X Denena et al.— Home Range and Movement of Nutria (Myocastor coypus) 5 Home Range corded from 27 days to 202 days obtaining eight to 53 unique points. This variation in number of unique points A total of 14 adult nutria, nine males and five per animal was due to radio collars falling off, the bat¬ females, was radio collared between 15 February, 2001 tery of the radio collars dying, the individual nutria and 21 September, 2001. Individuals were tracked leaving the study site, or the individual nutria dying. from 15 February, 2001 through 23 October, 2001. The home range size varied from 0.9 ha to 8.8 ha. Trapping continued through 7 November, 2001 in an The mean home range of the four females was 1.6 attempt to retrieve defunct radio collars. A total of hectares and 3.9 hectares for the four males. The overall 291 unique locations were recorded during this time mean home range of the nutria was 2.7 ha. A t-test period. A summary of home range (hectares) includ¬ was performed to determine if there was a significant ing the dates through which the individuals were difference in home range size between females and tracked, the number of locations obtained for each males (d.f. = 7, t = 1.26, P > 0,05), No significant individual, and the maximum linear distance traveled difference was detected. (meters) by each individual are presented in Table 2. The maximum linear distance traveled, per day, Home range was calculated for only eight (those from each individuals burrow for the eight nutria also with sufficient data to analyze) of the 14 nutria ( see was calculated. Maximum linear distances traveled Table 2). Of these eight nutria, locations were re¬ per day varied from 143 m to 475 m. The average Table 2. Home range estimates, and maximum linear distance traveled of radio collared nutria at Spring Lake, Hays County■ Texas, 2001. Key: * — indicates individual that was radio collared more than once. Individual Sex Date Ending Number of Home Range Maximum Reason Home number collared date Locations Estimate (ha) linear distance Range not used traveled N3 M Feb. 15 Jun. S 42 8.82 N4 F Feb.15 Sep. 4 47 1.14 _ N5 F* Feb. 16 May 16 53 0.96 - May 23 Aug. 20 N6 F Feb. 17 May 9 21 1.36 . N7 F Mar. 5 Aug. 7 4) 2.97 . N8 M Mar. 6 May 9 4 - Moved downstream N9 M Apr. I Apr. 19 7 - Animal died Nil M Apr. 27 7/16 24 2.14 _ N12 M* Jun. 25 Jun. 29 14 3.69 - Sep. 4 Oct. 23 N13 M Jun. 26 Aug. 20 14 - Collar fell off N14 F Sep. 1 Sep. 4 2 - Too few points N15 M Sep. 1 Sep. 13 4 - Too few points N16 M Sep. 7 Sep. 13 3 - Too few points N17 M Sep. 21 Oct. 17 8 0.86 - distance traveled by females was 217 m and males = 1.35, P > 0.05).. No significant difference was de¬ averaged 336 m. Three of the four females traveled tected. less than 169 meters, and all four males traveled over 202 m. A t-test was performed to determine if there Burrows of each individual were located within was a significant difference in maximum linear dis¬ their home range. Two of the females, N4 and N5, tance traveled between females and males (d.f. = 7, t shared a burrow on the northern bank of the slough. 6 Occasional Papers, Museum of Texas Tech University In the warmer months, these nutria did not spend day¬ The majority of the time when a collared indi¬ time hours in their burrow. They were found on nest¬ vidual was located, the nutria was resting; hidden along ing beds, padded down herbaceous vegetation cov¬ side the bank in vegetation. Many locations were re¬ ered by a canopy of shrubs or overhanging vegeta¬ corded with the individual swimming. At times, the tion, along the bank. Male N3 and female N6 also nutria would emit a loud, hom-like call while in the shared a burrow. This burrow was located at the base water: possibly a defense or warning call. Grooming of an uprooted tree in the slough. An unmarked juve¬ behavior also was observed. Nutria sat on the edge of nile nutria was observed entering this burrow along¬ the bank or in shallow water, grooming themselves. side N3. Female N7 and male N12 spent hours of This activity may have contributed to the fact that daylight enclosed by a cement path and a cement wall seven out of the total 14 collared animals slipped the located close to a vacant hotel near the headwaters of radio collar off of their neck. Many of the nutria looked the main lake. It was suspected that their “burrow” as though they lost weight over the summer. This was located in a pipe or drainage. Male Nil spent the also might have contributed to the fact that six out of majority of his time near man-made structures along¬ these seven collars fell off in late summer. Interac¬ side the main lake. During the day he slept under veg¬ tions with beaver also were observed. Nutria often etation or a dock in a wetland demonstration area. Male were located a few meters from the mouth of a beaver Nil also was seen during the day in hedges planted burrow. Juvenile nutria were observed swimming alongside a building. The burrow of N17, a male, was near feeding beaver. We did not observe any antago¬ located in the main lake, behind a cracked cement wall nistic interaction between the two species. in a densely vegetated area. Mortality Behavior Radio collars, equipped with a motality switch, Individuals were most active after sunset. Only indicated that two male nutria died during this study. two of the 14 nutria changed their daily activities due Male N9 was tracked for 19 days. Male Nil died to temperature. Females N4 and N5 reduced their after 81 days. activity during the hotter months. These two females remained on the south bank of the slough for the en¬ tire summer. All other nutria did not change their hab¬ its due to ambient temperature. Discussion Capture and Marking The nutria population was estimated at 16 indi¬ viduals using a modified Lincoln-Peterson Index. Based Nutria were easily captured during the nine-month on our field observations, this was an underestimate. period of trapping at Spring Lake—some repeatedly. A Nightly observations at the study site suggested that difference in behavior between sexes was observed the population was larger. while in the trap. Male nutria generally behaved ag¬ gressively, whereas most females were passive. Home Range Nutria at Spring Lake exhibit no sexual dimor¬ The overall mean home range of all nutria was phism in body size (Atwood, 1950). No significant 2.7 ha. The females had an average home range of difference between females and males regarding weight 1.6 ha and males averaged 3.8 ha. No significant dif¬ and linear lengths were found. Males averaged slightly ference in home range size was found between fe¬ heavier; the average weight of females was 4,4 kg and males and males in this study. Ryszkowski (1966) males averaged 5.1 kg, Ras (1999) had similar find¬ reported that females had more restricted movements ings with females having an average weight of 4.7 kg than males in a marsh in Warsaw, Poland. Ras (1999) and males averaging 5,2 kg. studied 73 radio collared nutria over a year at Tudor Denena et al.—Home Range and Movement of Nutria (Myocastor coypus) 1 Farms, Maryland, a private wildlife management area. had limited movements in the adjacent territory, both She found females to have an average home range of male. 0.11 km2 (11.0 ha) and males 0.09 torn2 (9.0 ha). Coreil (1984) studied seven radio collared nutria for a year in Burrows and nesting beds were dispersed a southwestern Louisiana marsh area and estimated an throughout Spring Lake. Four of the nutria, male N3, average minimum home range of 60 ha. Lohmeier female N4, female N5, and female N6, had typical un¬ (1981) estimated the mean home range of four radio derground burrows located at the water’s edge. Of collared nutria, two males (2.3 ha) and two females these, N4 and N6 spent daylight hours in summer sleep¬ (2.4 ha), to be 2.3 ha in a pond in the Hillside National ing on various nesting beds. These two nutria stayed Wildlife Refuge in Mississippi. Kays (1956) studied within a few meters of one another throughout the the ecology of nutria at Rockefeller State Wildlife Ref¬ entire study. Gosling and Baker (1988) found female uge in Louisiana and estimated the maximum home nutria stayed near their mother and formed a cluster range of nutria to be 1,097 m2 (0.1 ha). or kin group. Three nutria, female N7, male N12, and male N17, took advantage of man-made cement walls. Variances in home range sizes between studies These burrows were similar to those found by Atwood may be due primarily to differences in the study area. (1950) involving levees, dikes, and ditchbanks. Male Spring Lake most closely resembled the study site used N17 spent his daylight hours in or near man-made struc¬ by Lohmeier (1981). The area used in this study was tures. Male nutria Nil, also stayed around man-made a small 8 ha lake, similar to the 5 ha pond in the Hillside structures, and was seen several times walking near National Wildlife Refuge; unlike the 2,430 ha Tudor buildings on the property and in a parking lot. Other Farms (Ras, 1999) and the 34,000 ha Louisiana marsh nutria remained in burrows or on nesting mats during (Coreil, 1984), Nutria utilized the area available to them. the day. Guichon and Cassini (1999) studied nutria in Spring Lake was suiTOunded by a golf course, softball their native habitat in Argentina and found they avoided fields, many roads, and a nearby university. This lake areas with human disturbance, “i.e., docks, houses, also had restricted emergent vegetation and no marsh roads, recreational centers.” Out of the eight collared regions, resulting in limited foraging resources. There¬ nutria, three, female N4, female N5, and male Nil, fore, nutria at Spring Lake almost exclusively foraged had multiple burrows or nesting beds. Ryszkowski on the floating and submersed vegetation (Towns, (1965) found 39 percent of 69 nutria occupied more 2002). than one shelter. Nutria in the study by Ras (1999) traveled from Behavior 30 m to 1500 m. Ras also reported that there was no significant difference in distances traveled by females Nutria at Spring Lake were active from dusk until and males. Coreil (1984) reported the average daily dawn and only seldom seen during daylight hours. movement to be 718 m. Robicheaux (1978) studied Two females, N4 and N5, reduced their activity dur¬ nutria at Rockefeller State Wildlife Refuge in Louisiana ing the hot summer months. The remaining six nutria and found the average linear distance traveled by nu¬ did not change their habits in relation to ambient tem¬ tria was 226 m. In Robicheaux's study, 80.4 percent perature. Chabreck (1962) reported no change in nu¬ of all nutria traveled less than 400 m. Adams (1956) tria activity, in Louisiana, based on air temperature. suggested that nutria’s daily cruising range did not Coreil (1984), also studying nutria in Louisiana, re¬ exceed 183 m. Variances between studies may have ported that movement rates of nutria were greatest in been primarily due to differences in study sites. the winter and home range estimates were larger in winter and spring. Results of previous studies suggest that nutria did not exhibit territorial behavior except near the nest¬ The periodical calling by the nutria has been ob¬ ing site (Coreil, 1984;Ryszkowski, 1966). In this study, served in other studies. Warkentin (1968) observed the home ranges of the nutria were restricted due to nutria “mooing” in a threatening manner. We found territoriality according to the definition given by Grier male nutria retreated when approached by a human and Burk (1992). Overall, the individuals stayed either and gave a hom-like call. in the slough or in the main stream. Two of the eight 8 Occasional Papers, Museum of Texas Tech University Nutria were observed grooming several times. sive Species Council: a Council responsible for over¬ Grooming may have contributed to the loss of radio seeing the control of invasive species by providing lead¬ collars because the vigorous grooming may have ership, working with Federal, State, and International caused the collars and or antennae to loosen an dis¬ agencies, and implementing an Invasive Species Man¬ lodge. Weight loss also may have contributed to collar agement Plan (Clinton, 1999). loss. Bounds et al. (2001) reported problems with nutria slipping radio collars off as a result of fluctuat¬ Many research projects have been conducted or ing weight. are studying nutria. For instance, a three-year pilot project in Maryland began in January 2001 radio col¬ Management Implications laring 225 nutria. This project hopes to gather enough information about nutria ecology to eradicate them A 1998 survey concerning the presence or ab¬ from the state (Bounds et al., 2001). It was modeled sence of nutria was given to state Departments of after a study in Great Britain where nutria were suc¬ Natural Resource Agencies (hereafter DNRs) and Na¬ cessfully eradicated (Gosling, 1989). Gosling’s rec¬ tional Wildlife Refuges (hereafter NWRs) in the 48 ommendations for successful eradication were “de¬ contiguous states. Nutria were present in 15 states. velop a pilot eradication program; study nutria move¬ Out of these, only 20 percent of the DNRs and 9 per¬ ments; develop accurate population estimates; and ini¬ cent of the NWRs had conducted research on nutria. tiate a proactive public relations campaign” (Bounds et However, 53 percent of the DNRs and 56 percent of al., 2001). the NWRs reported that native species were affected by the presence of nutria (Bounds, 2000). Our study provides information about the daily activities of nutria in Texas. Studies on territory and A number of measures are being taken to try to home range in this state have not previously been docu¬ control the invasive nutria. On 3 February, 1999, Ex¬ mented. Knowing the basic ecology of an invasive ecutive Order 13112 was signed by President William species is the first step in understanding how to con¬ J. Clinton. This order established the National Inva¬ trol their populations. Comments on Home Range and Movement of Beaver (Castor canadensis) at Spring Lake in Central Texas American beaver (Castor canadensis) are native Beaver were trapped using two 99x53 cm Toma¬ semi-aquatic rodents also found at Spring Lake. Bea¬ hawk Bailey beaver traps (Tomahawk Live Trap Com¬ ver occupy all of the United States excluding a portion pany, Model #801), a medium (107 x 38 x 51 cm) of Florida and the southwestern desert (Jenkins and Tomahawk live trap (Tomahawk Live Trap Company, Busher 1979). The beaver at Spring Lake do not build Model #109,5), and a large (152 x 51 x 66 cm) Toma¬ dams, but burrow into the bank. hawk live trap (Tomahawk Live Trap Company; Model #110B). These traps were set along the shores of Different methods for successfully radio mark¬ Spring Lake either on the bank or in shallow water in ing beaver have been explored. Davis et al., (1984), 21 different locations from 29 November, 2000, Reinke (1986) and Guynn et al., (1987) surgically im¬ through 5 February, 2001. Over a total of 194 trap planted transmitters under the skin of beaver. This nights, three beaver were caught. Manufactured cas¬ was proven to be a successful method. Rothmeyer et tor was used to bait the traps. Once a beaver was in a al., (2001) effectively tested a modified ear-tag for trap, the same data collection methods used for the use as a radio telemetry transmitter. In 1975, Busher nutria were executed. followed seven beaver in California with radio trans¬ mitters tied around the base of their tails. Lancia (1979) Home range was calculated using minimum con¬ radio collared and tracked 14 beaver in Massachusetts. vex polygons for two beaver, male B1 and female B2. Denena et al.—Home Range and Movement of Nutria (Myocastor corpus) 9 Their mean home range was 3.7 ha. Maximum linear times the trigger was knocked down, but the trap would distance traveled by the three beaver ranged from 198 not spring or only one side of the trap would spring. m to 1966 m. Traps also were found empty or triggered by a cut branch the beaver was carrying. Female B2 never left the boundaries of Spring Lake, primarily staying around the mouth of her bur* The collars also were damaged soon after they row. On multiple occasions, male B1 would travel were placed on the beaver. Male B1 was tracked for beyond the dam of the lake. On these nights, a loca¬ 138 days. On day 69 the collar began to malfunction; tion was not recorded. B1 and B2 shared a burrow on some nights the mortality switch or a sporadic signal the south bank of the slough. At least two other un- would be emitted while the animal was observed feed¬ marked adult beaver shared this burrow. In summer ing or swimming. The battery of female B2's collar 2001, three kits were observed at this site. Female B3 died after 87 days. This animal was observed on later was trapped on the bank of the Spring Lake dam. Her dates with the collar intact around her neck. Tire col¬ burrow was later located 1966.05 m downstream. A lar on female B3 stopped broadcasting a signal after signal was not detected near Spring Lake following being followed for 38 days. One of these collars was her initial capture. recovered. The collar had teeth marks which cracked the waterproof seal around the transmitter. We sus¬ Trapping beaver was difficult and unproductive. pect these beaver would bite the collars while groom¬ The beaver would avoid traps even when they were in ing one another; therefore, we do not think radio col¬ an area of high activity. Also, the Tomahawk Bailey lars are the best method for radio tracking beaver. Sur¬ beaver traps malfunctioned many times due to the traps gical implants would allow the individuals to be fol¬ being difficult to set at the desired sensitivity. Multiple lowed for a longer period of time. Literature Cited Adams, W. H., Jr. 1956. The nutria in coastal Louisiana. Busher, P. E. 1975. Movements and activities of beavers, Louisiana Academy of Sciences, 19:28-41. Castor canadensis, on Sagehen Creek, Califor¬ nia. Unpublished M.S. Thesis. San Francisco Aguirre, P. B. 1999. Space use patterns of the common State University, San Francisco, California. 86 snapping turtle (Chelydra serpentina serpentina) at the headwaters of the San Marcos PP- River, Hays County, Texas. Unpublished M.S. Ch abreck, R. H. 1962. Daily activityofnutriainLouisiana. Thesis. Southwest Texas State University, San Journal of Mammalogy, 43:337-344. Marcos, Texas. 38 pp. Clinton, W. J. 1999. Executive Order 13112 of February 3, Atwood, E. L. 1950. Life history studies of nutria, or 1999 - Invasive Species. National Agricultural coypu, in coastal Louisiana. Journal of Wildlife Library ofU.S, Department of Agriculture, http:/ Management, 14:249-265. / www. in vas i vesp e ci es. gov/1 aw s/execord er. shtml. Bo, R. F., F. Palomares, J. F. Beltran, G de Fillafane, and S, Cochran, W. W., and R. D. Lord, Jr. 1963. A radio-tracking Moreno, 1994. Immobilization of coypus systemforwildanimals. JoumalofWildlifeMan¬ (Myocastor coypus) with ketamine hydrochlo¬ agement, 27:9-24. ride and xylazine hydrochloride. Journal of Wild¬ Coley, R. 2000. Aquarena Center. Southwest Texas State life Diseases, 30:596-598. University, http: //w w w. c on tinuin g- ed,swt.edu/ Bounds, D, L. 2000. Nutria: an invasive species of na¬ aquarena/ (25 November, 2000). tional concern. Wetland Journal, 12:9-15. CoTeil, P. D, 1984, Habitat preferences, movements, and Bounds, D. L., T. A. Mollett, and M. H. Sherfy. 2001. The activities of adult female nutria in a southwest¬ nutria nuisance in Maryland and the search for ern Louisiana intermediate marsh area. Unpub¬ solutions. Aquatic Nuisance Species Digest, lished M.S, Thesis. Louisiana State University, 4:25-31. Baton Rouge, Louisiana. 123 pp. Brune, G. 1981. The Springs of Texas. Vol, 1. Branch- Smith, Inc., Fort Worth, Texas. 566 pp. 10 Occasional Papers, Museum of Texas Tech University Corei], R D., and H. R. Peny, Jr, 1977, A collar for attaching Kays, C. E. 1956, An ecological study with emphasis on radio transmitters to nutria. Proceedings of the nutria (Myocastor coypus) in the vicinity of Price Annual Conference Southeastern Association of Lake, Rockefeller Refuge, Cameron Parish, Loui¬ Fish and Wildlife Agencies, 31:254-258, siana. Unpublished M.S. Thesis. Louisiana State Davis, J. R., A. F, Von Recum, D. D, Smith, and D, C, Guynn, University, Baton Rouge, Louisiana, 145 pp. Jr. 1984. Implantable telemetry in beaver. Wild¬ Lancia, R. A. 1979. Year-long activity patterns of radio- life Society Bulletin, 12:322-324. marked beaver (Castor canadensis). Unpub¬ Evans, J. 1970. About nutria and their control. U.S. Fish lished Dissertation. University of Massachu¬ and Wildlife Service Resource Publication, 86:1- setts, Amherst, Massachusetts. 131 pp. 65. Litvaitis, J. A., K. Titus, and E. M. Anderson. 1996. Mea¬ Gosling, L. M. 1989. Extinction to order. New Scientist, 4 suring vertebrate use of terrestrial habitats and March:44-49. foods, Pp. 254-274 in Research and Manage¬ ment Techniques for Wildlife and Habitats (T. A. Gosling, L. M., and S. J. Baker. 1988. Demographic conse¬ Bookhout, ed.). The Wildlife Society, Bethesda, quences of differences in the ranging behavior Maryland, 740 pp. of male and female coypus. Coypus Research Laboratory, Norwhich, United Kingdom, 11 pp. Lohmeier, L. 1981. Home range, movements, and popula¬ tion density of nutria on a Mississippi pond. Grier, J. W., and T. Burk. 1992. Biology of Animal Behav¬ Journal of the Mississippi Academy of Sciences, ior. Mosby Year Book, St. Louis, Missouri. 890 26:50-54. pp. Milne, R. C. 1963. A habitat description and evaluation, Groeger, A. W., P. F. Brown, T. E Tietjen, and T, C. Kelsey. semiquantitative food habit analysis, and popu¬ 1997. Water quality of the San Marcos River. lation study of the nutria, Myocastor coypus Texas Journal of Science, 49:279-294. (Molina) Kerr, on Hatteras Island, North Caro¬ Guichon, M, L., and M. H. Cassini, 1999. Local determi¬ lina. Unpublished M.S. Thesis. North Carolina nants of coypu distribution along the Lujan River, State College, Raleigh, North Carolina. 116 pp. eastcentral Argentina. Journal of Wildlife Man¬ Nichols, J. P., and M. Conroy. 1996. Techniques for esti¬ agement, 63:895-900. mating abundance and species richness. Pp. 177- Guynn, D. C., Jr., J. R, Davis, and A, F, Von Recum. 1987. 234 in Measuring and Monitoring Biological Di¬ Pathological potential of intraperitoneal trans¬ versity; Standard Methods for Mammals (D. E. mitter implants in beavers. Journal of Wildlife Wilson, E, R. Cole, J. D. Nichols, R. Rudran, and Management, 51:605-606. M.S, Foster, eds.). Smithsonian Institution Press, Washington and London, England, xxiii + 409. Hediger, H. 1970. The breeding behavior of the Canadian beaver (Castor fiber canadensis). Forma et Nyman, J, A., R. H. Chabreck, and N. W, Kinler. 1993. Functio, 2:336-351. Some effects of herbivory and 30 years of weir management on emergent vegetation in brackish Hill, E, P. 1982. Beaver. Pp. 256-281 in Wild Mammals of marsh. Wetlands, 13:165-175. North America: Biology, Management and Eco¬ nomics (J, A. Chapman and G A. Feldhamer, eds.). Ostro, L. E. T,, T. P. Young, S. C, Silver, and F. W. Koontz. John Hopkins University Press, Baltimore, Mary¬ 1999. A geographic information system method land. xiii+ 1147. for estimating home range size. Journal of Wild¬ life Management, 63:748-755. Hudson, J. M. 1999. Home range of the raccoon (Procyon lotor), and the degree of interaction with domes¬ Powell, R. A. 2000. Animal home ranges and territories tic pets at Aquarena Center, San Marcos, Hays and home range estimators. Pp. 65-110 in Re¬ County, Texas. Unpublished M.S. Thesis. South¬ search Techniques in Animal Ecology; Contro¬ west Texas State University, San Marcos, Texas. versies and Consequences (L. Boitani and T. K. 24 pp. Fuller, eds.). Columbia University Press, New York, New York. 446 pp. Jenkins, S. H., and P, E. Busher. 1979, Castor canadensis. Mammalian Species, 120:1-8. Ragan, J, G. 1960. Poison baits for nutria control. Unpub¬ lished M.S. Thesis. The University of South¬ Kainer, M. A. 1992. Woody plant use and preferences by western Louisiana, Lafayette, Louisiana, 34 pp. the American beaver (Castor canadensis) in Cen¬ tral Texas, Unpublished M.S, Thesis. South¬ west Texas State University, San Marcos, Texas. 62 pp.