Home ranges and movement characteristics of minks in East-central New York.
Reliable space use information is necessary for understanding the population ecology of a species, for monitoring population trends, and for achieving desired management goals. Although minks (Neovison vison) are relatively common riparian carnivores that are distributed throughout much of North America, studies of space use for native minks are very limited (Lariviere, 2003). For minks that occupy river systems, home ranges are most frequently presented as linear estimates due to most of their activity occurring near water (Gerell, 1970; Stevens et al., 1997). However, the only two available linear home range and movement studies of native minks either were limited by low sample size (n = 3 males; Stevens et al., 1997) or excluded tributaries, which minks commonly use (Whitman, 1981).
American minks have been more extensively researched outside of North America where escapes from fur farms have resulted in the establishment of invasive populations throughout Europe and other regions (Lariviere, 2003). Although a number of invasive mink studies have evaluated space use, comparisons between native and invasive populations may be tenuous (Wright et al., 2010). Furthermore, the objectives of many invasive mink studies relate to either evaluating impacts on native species or methods for controlling or eradicating invasive minks (Zuberogoitia et al, 2010; Melero et al., 2012; Reynolds et al., 2013). Because home range and movement information for native minks is limited, our objectives were to quantify and analyze both linear home range sizes and daily movement distances of minks between the Hudson River and its tributaries.
STUDY SITE DESCRIPTION
The study area was located in east-central New York and was focused along an approximately 46 km reach of the Hudson River from just south of Bridge Street (County Road 27) in Hudson Falls (43[degrees]16'59"N, 73[degrees]35'50"W) to just south of the Hudson and Hoosic Rivers junction near Mechanicville (42[degrees]55'40"N, 73[degrees]39'52"W), New York. Hudson River tributaries along the 46 km reach were also included, but extended no farther than 8.5 km of waterway distance from the Hudson River. The Hudson River is much larger than its tributaries within the study area. In most places, the Hudson River was 150-225 m wide, whereas most of the tributaries were 2-10 m wide. Nearly all of the research was conducted on private lands and included parts of Saratoga, Washington, and Rensselaer Counties. This area is characterized by moderate urbanization with abundant cropland and mixed fragmented forests. Average annual precipitation consists of 99 cm of rain and 172 cm of snow. Average temperature in summer is 19 C and -6 C in winter (NOAA, 2013).
CAPTURE AND TELEMETRY
We captured minks along the Hudson River and its tributaries using Tomahawk double-door box traps (Tomahawk Live Trap, Tomahawk, Wisconsin). Capture and telemetry methods are further described in Haan and Halbrook (2014). We transported minks to a centrally located veterinary clinic where they were anesthetized. We then recorded standard body measurements, attached an ear tag, and dorsally implanted a subcutaneous (Lander et al, 2005) radiotransmitter (5 g or 9 g; 5-18 mo battery life; Holohil Systems Ltd., Ontario, Canada). After we closed the incision and administered an antibiotic, we returned and released minks at their capture sites. Capture and handling procedures followed an approved Animal Care and Use Protocol by Southern Illinois University and permit requirements issued by the New York State Department of Environmental Conservation for all capture and handling procedures, which also met the American Society of Mammalogists animal care guidelines (Gannon et al, 2007).
We radio-tracked minks using the homing technique as described by Mech (1983), from Mar. to Jun. 2008 and 2009, and from Mar. 2010 to Sep. 2011. Minks were radiotracked at different times between dawn and dusk (Stevens et al, 1997). When minks were inactive, we marked their resting site location, whereas when minks were active we quietly approached to within 10 m (estimated based on signal strength) and marked the mink's approximate location to minimize disturbance. We marked all mink locations using a handheld GPS (Garmin International, Inc., Olathe, Kansas, USA; Model: Garmin eTrex).
We considered mink home ranges to be linear distances along waterways where most mink activity occurs (Whitman, 1981; Stevens et al, 1997; Zabala et al, 2007b). We recorded the minimum linear waterway distances in ArcGIS 9.2 (ESR1 Corporation, Redlands, California, USA) using digital orthophoto quadrangle (DOQ) aerial photos (Zabala et al, 2007b; Ahlers et al, 2010) and referenced digital raster graphic (DRG) topographic maps when canopy cover obscured small stream channels. We differentiated between home ranges along the Hudson River and its tributaries (including stream orders 1-4; Strahler, 1957). For our home range estimates we used only minks with at least 1 location recorded on [greater than or equal to] 20 separate days and included 100% of the locations (Zabala et al, 2007a).
We estimated daily movement distances by measuring waterway distance between locations on consecutive days. We measured daily movement distances between locations in the same manner as home ranges and again differentiated between movements along the Hudson River and tributaries. Minks that were found at the same location on consecutive days and females that exhibited maternal denning behavior were not included in the analysis; rather we indicated the frequency of those occasions separately. We also assessed the frequency and river widths for occasions when minks swam across the Hudson River. Because we did not know the exact locations where crossings occurred, we took an average of three river width measurements (shortest distance) in ArcGIS 9.2 including the immediate pre-and post crossing locations and a third measurement centered between the pre-and post crossing locations.
We evaluated for differences in the proportion of mink home ranges along the Hudson River and its tributaries. In this evaluation, we included only minks whose home ranges encompassed portions of both the Hudson River and its tributaries. We also tested for home range differences between minks that used both waterbody types and minks that only used tributaries, and tested for overall (waterbody types combined) home range differences between males and females. For movement characteristics, we evaluated differences in daily movement distances between the Hudson River and tributaries and tested for differences in movement distances between males and females. Data were not normally distributed; therefore, we used the Wilcoxon rank-sum test for all analyses (Zar, 2010). We performed all statistical tests using SAS version 9.1 (SAS Institute, Inc., Cary, North Carolina, U.S.A.). Means are followed by [+ or -] Standard Error (se).
We implanted radiotransmitters in 35 (24M, 11F) captured minks and estimated home ranges for 23 (15M, 8F) minks ([bar.x] = 65.7 [+ or -] 9.2 telemetry locations on different days/mink). We were not able to acquire sufficient locations to estimate home ranges for 10 (8M, 2F) minks due to transmitter dislodgement (n = 7) and predation (n = 3), but we did use movement data from these 10 minks along with the other 23 minks as part of our daily movement distance analyses (Fig. 1). Additionally, we did not obtain any data for two minks due to predation 1 and 6 d following capture. Mean body weight among all captured males and females was 759 [+ or -] 32 g and 480 [+ or -] 27 g, respectively.
Twelve of the 23 minks analyzed for home ranges used the Hudson River. All 12 of these minks also used portions of its tributaries. The mean home range proportions for these 12 minks along the Hudson River and its tributaries was 2.7 km and 3.0 km, respectively, and was not significantly different (Wilcoxon: [F.sub.24] = 0.14, P = 0.716). The remaining 11 minks stricdy used tributaries and the test to compare home range size between minks that used both waterbody types with those that only used tributaries was also not significantly different (Wilcoxon: [F.sub.23] = 1.23, P = 0.280). However, a comparison between sexes revealed that males had significantly larger overall home ranges than females (Wilcoxon: [F.sub.23] = 4.85, P = 0.039; Table 1). Overall home range sizes for males were between 3.2-8.4 km and 1.76.5 km for females.
Daily movement distances by all minks along tributaries ([bar.x] = 732 [+ or -] 26 m) were significantly greater than along the Hudson River ([bar.x] = 532 [+ or -] 29 m; Wilcoxon: [F.sub.887] = 20.65, P < 0.001). Males had significantly greater daily movement distances than females along both the Hudson River (Wilcoxon: [F.sub.265] = 15.63, P < 0.001) and tributaries (Wilcoxon: F6i8 = 11.72, P < 0.001; Fig. 2). Males and females traveled >2.0 km daily on 8% and 0.4% of occasions, respectively, and the farthest single daily movement was 3.1 km by a male. For minks along the Hudson River, we located them on the opposite shoreline as the previous day on 9.5% of telemetry locations with a mean river width of 164 [+ or -] 6.6 m (range 52-229) at crossings.
We found nonmaternal denning minks at the same location as the previous day on 17% of occasions and for >2 consecutive days on only 4% of occasions with 6 d as the longest. We located a female mink in 2010 and another in 2011 at maternal den sites from 24 Apr. to 5 Jun. The female in 2010 remained at one den site for 28 consecutive days. The female in 2011 remained at one den site for 13 consecutive days, then moved 278 m overnight to a different den site and stayed there for an additional 14 consecutive days.
The similar home range sizes between the Hudson River and tributaries for minks that used both waterbody types suggest that minks may not select for either type. This may relate to the ability of minks to catch a diversity of terrestrial and aquatic prey, thereby allowing them to utilize a wide range of riverine habitats. For minks that used the Hudson River, we located the three females along the river with the same regularity as the nine males; furthermore the females had a higher proportion of their home range along the Hudson River than the males. This contrasts from an invasive American mink study by Zabala et al. (2007a) in northern Spain that indicated females largely used main streams as corridors to access tributaries, whereas males mostly used main streams and only marginally used tributaries.
The mean percent home range use along tributaries among our nine male minks that used both waterbody types was 21% greater than the three males monitored by Stevens et al. (1997) that also used both main river channels and tributaries in Tennessee. The mean overall home range estimate for males in our study (5.8 km) was less than the 7.5 km estimate for the three males by Stevens et al. (1997). However, our overall (all minks) home range estimate (5.2 km) was 1.2 km greater than what Whitman (1981) reported for 21 minks in Idaho, which excluded tributaries. The most comparable home range estimate is from an invasive mink study in northern Spain by Zabala et al. (2007a) that reported a home range of 5.8 km for seven minks that similarly included main river channels and tributaries.
The significant difference between male and female home range size in our study is consistent with Whitman (1981), although males in his study had a home range size that was more than twice that of females, 4.6 km and 2.0 km, respectively. Invasive mink studies have also indicated males generally have larger home ranges than females (Birks and Linn, 1982; Yamaguchi and Macdonald, 2003; Zabala et al, 2007a). The larger mass of males compared to females (33% in our study) likely necessitates larger home ranges and greater daily movement distances to obtain sufficient prey to meet energetic demands (Dunstone, 1993) or to maximize home range overlap with females for breeding (Zschille et al., 2012).
Because our daily movement estimates could not account for various travel patterns by minks such as meandering and backtracking, we considered our daily movement distances to be the length of shoreline traversed by minks from one day to the next. Although home range size was similar between the Hudson River and tributaries for minks that used both, it appeared that minks along tributaries tended to travel farther on a daily basis than they did along the Hudson River. The density of foraging sites may tend to be greater along the Hudson River, which may limit the daily movement distances of minks, whereas small and shallow tributary reaches would presumably have lower densities of aquatic prey and may therefore cause minks to travel farther to reach suitable foraging areas. The longest daily movement in our study was 3.1 km, which was less than the 4.3 km reported by Stevens et al. (1997) for minks in Tennessee and also less than the 12.0 km straight-line distance reported by Arnold and Fritzell (1987) for prairie minks in Manitoba, Canada.
This is the only known published study to evaluate home ranges and daily movement distances of native minks along a large river system and will provide managers with much needed space use information for native minks. Our study shows that minks of both sexes readily use the Hudson River as well as its tributaries and that the proportion of mink home ranges along both waterbodies was similar. Daily movement distances by minks; however, tended to be greater along tributaries than along the Hudson River, which may indicate lower prey densities along tributaries. This may be especially true for the smaller tributaries where aquatic prey would be most limited. Our overall home range estimates were between the only two available native mink studies that provided linear home range estimates; however, our study provides a more ideal sample size and incorporates tributaries as well as the main river channel.
Acknowledgments.--The General Electric Company provided the funds for this research. We owe much gratitude to the hardworking technicians involved with this research including H. Cimino, J. D'Agostino, A. Goldberg, K. Grmusich, J. Histed, S. McKenzie, A. VanVossen, W. White, and further assistance provided by T. McClenahan and P. Bernstein. We are thankful to G. Allen, M. Horn, and the entire staff of the Battenkill Veterinary Clinic as well as the many gracious property owners in our study area that granted us access to their land. We also thank C. Nielsen, J. Reeve, the Cooperative Wildlife Research Laboratory, the Department of Zoology, and the Graduate School at Southern Illinois University for their guidance and support.
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SUBMITTED 16 SEPTEMBER 2014
ACCEPTED 11 JUNE 2015
DAMON M. HAAN (1) and RICHARD S. HALBROOK
Cooperative Wildlife Research Laboratory, Department of Zoology, Southern Illinois University, Carbondale 62901
(1) Corresponding author: Telephone: 605-254-2946; e-mail: email@example.com
TABLE 1.--Mean linear home range sizes (km) for minks (Neovison vison) that used both the Hudson River (HR) and its tributaries (TR), in east-central New York (proportion of each waterbody type in parenthesis), minks that used tributaries only, and overall (waterbody types combined) in east-central New York, 2008-2011. Males had a significantly larger overall home range than females (P = 0.039) Both (HR:TR) Tributaries only n = 12 (9M, 3F) n = 11 (6M, 5F) Sex [bar.x] [+ or -] SE [bar.x] [+ or -] SK Males 6.0 [+ or -] 0.6 (2.8:3.2) 5.6 [+ or -] 0.8 Females 4.7 [+ or -] 0.9 (2.4:23) 3.7 [+ or -] 1.0 All Minks 5.7 [+ or -] 0.5 (2.73.0) 4.7 [+ or -] 0.7 Overall n = 23 (15M, 8F) Sex [bar.x] [+ or -] SE Males 5.8 [+ or -] 0.5 Females 4.1 [+ or -] 0.7 All Minks 5.2 [+ or -] 0.4
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|Author:||Haan, Damon M.; Halbrook, Richard S.|
|Publication:||The American Midland Naturalist|
|Date:||Oct 1, 2015|
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