Discussion
Introduction
Some gray wolves (Canis lupus) travel to areas over 800 km away from
their packs (Mech and Frenzel, 1971; Fritts and Mech, 1981; Fritts, 1983;
Messier, 1985; Mech, 1987). Until recently it has been technologically or
financially difficult to determine the detailed routes of these wolves because
of the distances involved. Often, the only information available is the starting
point based on where a wolf was originally captured and marked and the ending
point based on a capture, road-kill or other type of recovery reported later
(Berg and Kuehn, 1982; Ballard et al., 1983; Fritts, 1983; Mech et al.,
1995; Wydeven et al., 1995). Recently, however, newer technology such as
satellite tracking (Fancy et al., 1988; Ballard et al., 1995) and
Global Positioning System (GPS) collars suitable for wolves (Merrill et al.,
1998) have yielded detailed descriptions of wolf routes. These more detailed
descriptions allow a better understanding of wolf travels and extraterritorial
movements and suggest new questions about such movements (Mech, 1995). Using
GPS, satellite and aerial VHF telemetry, we provide descriptions of four wolf
travel routes.
Study Area
One wolf in our study left from the east-central Superior National
Forest (48°N, 92°W) in northeastern Minnesota, where the terrain is flat with
low ridges and the vegetation consists primarily of cut-over transitional
deciduous and boreal forest (Mech, 1987). The area has long been saturated with
wolf pack territories (Mech, 1973, 1986). Three other wolves made long
extraterritorial movements from a wolf population at Camp Ripley, a 21,400 ha
National Guard Training Site in Little Falls, Minnesota (46°N, 95°W) at the
southern edge of wolf range. The terrain is generally flat and the major cover
is northern hardwood forest (primarily Quercus, Populus and Betula
spp.) interspersed with large open areas (grasslands, wetlands and military
firing ranges). Camp Ripley is located at the prairie-forest transition zone of
central Minnesota. It is surrounded on the east and south by agricultural lands,
and on the north and west by forest interspersed with agricultural development.
Methods
Male wolf 2480 (
18-mo
old; ages estimated by tooth wear) was live-trapped in a modified steel
foot-trap on 1 November 1972, anesthetized, collared with a 540 g standard VHF
radio-collar and aerially radio-tracked weekly (Mech, 1974). He was a member of
a pack of 12 wolves that lived 20 km west of Ely, Minnesota.
On 3 February 1998 male wolf 5399 (18-mo
old) born at Camp Ripley was captured by helicopter net-gunning. A 920 g GPS
collar (Merrill et al., 1998) was placed on the wolf and the wolf was
released. The collar had been programmed to acquire a GPS location every 3 h. If
no location was recorded, the GPS collar tried again in 15 min and 30 min. If
all three attempts failed, further attempts were not made until the next
programmed interval. We dropped the collar off the wolf via remote signal (Mech et
al., 1990), homed in on its VHF signal, collected the collar and downloaded
the data (Merrill et al., 1998).
A 560 g satellite collar with a stiff external whip antenna (Microwave
Telemetry Inc., Columbia, Maryland) was placed on male wolf 7803 (10-mo old),
which had been captured by helicopter net-gunning at Camp Ripley on 1 February
1998. After retrieval and refurbishing, the collar was placed on female wolf
7804 (2-y old; aged by following her with a VHF radio since she was a pup) on 3
February 1999. With both wolves, the collar was programmed for the following
duty cycle: first 5 mo, 12 h on (transmitting a signal), 24 h off; remainder of
collar life, 12 h on, 72 h off. ArcView© geographic information system (ESRI
Inc., Redlands, California) was used to create maps and calculate distances
traveled and the number of times wolves crossed state, provincial and interstate
highways.
Results
We located wolf 2480 at 28 locations in his pack territory from 13
November 1972 through 21 March 1973; then on 26 March 1973 the wolf was located
12 km north of his territory, his first extraterritorial location. After that,
the wolf was located 17 times through 30 June 1973 away from his pack's
territory and traveled almost exclusively through wilderness (we recorded only
one highway crossing). He returned to within 8 km of his pack territory after 1
mo (Fig. 1). Because of the infrequent radio-tracking, wolf 2480 could well have
visited the pack without our having detected it. We do not know if the first
trip was a predispersal foray or an actual dispersal.
After 19 April 1973 wolf 2480 moved north again and then west through Ontario
to a more open area (17 May 1973) with more roads and humans and eventually to
the east shore of Lake-of-the-Woods. He traveled northeastward parallel with the
shore for about 40 km and then the signal emanated from the same location for 2
wk, so a ground check was made. The collar was found by itself, with no
indication of what happened to the wolf.
| FIG. 1. Long-distance travel routes
of four wolves collared in Minnesota. Double line = wolf 2480, thin
single line = wolf 5399, dashed line = wolf 7803 (killed), thick solid
line = wolf 7804 (killed). Shaded area represents 1998 range of breeding
wolves |
Satellite-collared wolf 7803 left his territory on 12 September 1998 headed
directly away from the known wolf breeding range (Fig. 1). His collar collected
55 locations during movements through agricultural areas before he was shot by a
coyote (Canis latrans) hunter near Howard Lake, MN on 14 November 1998.
He made at least 33 highway crossings. Wolf 7804, also satellite-collared, left
on 26 March 1999; during her travels the wolf stopped directional movement for
37 d between Wisconsin Dells and Stevens Point (Fig. 1). This area includes
several rugged wetlands with low human presence. The collar collected 274
locations by 21 September, when the wolf returned to Camp Ripley. On 25
September the wolf left again, settled about 40 km east of Camp Ripley and was
killed illegally on about 11 November 1999. She made at least 215 highway
crossings.
The GPS collar on male wolf 5399 collected 1121 locations on 57 days of the
animal's extraterritorial trips. The wolf left the territory on 31 May 1998 and
traveled an average of at least 3.55 km/h (n = 220 line segments) during his
trip. He made at least 17 highway crossings. He returned to near his natal
territory and, therefore, we considered the long movement an extraterritorial
foray (Messier, 1985). The wolf may have rejoined the pack shortly after the
collar was dropped.
No data are available that would allow an estimate of the proportion of
wolves in the populations studied that make long distance moves because: (1)
with one wolf (2480), a special effort was made to follow it wherever it went,
whereas no such effort was made for other wolves in that study, (2) wolf 5399
was part of a very small sample on which GPS collars were tested (Merrill et
al. 1998) and (3) with the last two wolves (7803 and 7804), a special effort
was made to select predispersal individuals (nonalpha, at least 1-y old wolves)
on which to place the satellite collars.
Discussion
The four wolves studied all traveled far from their pack territories.
Wolves 7803 and 7804 left the territories in which they were born. Although we
were unable to document that the other two wolves were born into the packs whose
territories they left, that is likely the case (Fritts and Mech, 1981; Mech,
1987; Fuller, 1989; Gese and Mech, 1991).
All four wolves also returned to their territories or nearby after travels as
far away as 494 km and periods up to 179 d. Two of the four then left again; one
remained about 40 km from its territory for 9 wk (wolf 7804, 7/29 - 9/21); we
could not follow the fourth wolf after its return. Wolves returning to their
natal territories after long periods away have been documented before (Fritts
and Mech, 1981; Messier, 1985; Mech, 1987; Mech and Seal, 1987; Fuller 1989).
In two cases, the wolves we followed made large loops to return, whereas one
wolf (wolf 5399) returned on almost the same route by which it had left (Fig.
1). The loop returns suggest that even at distances of 494 km from their
territory and for absences as long as 179 d, wolves remember their territory
location. This finding extends earlier work showing that wolves moved as far as
63 km from their capture points for as long as 24 d can return (Fritts et al.,
1984).
Several remaining questions about distant wolf travels include "What
constitutes wolf travel barriers?," "Are there travel corridors
(Hobbs, 1992) that wolves favor?," and "To what extent do wolf
populations adapt to travel barriers and corridors?" (Mech, 1995). With
aerial VHF telemetry, relatively few locations are obtainable during long wolf
travels (Table 1), so these questions are difficult to address. Satellite and
GPS telemetry, however, provide the first opportunity to examine these questions
in greater detail.
| Table 1.
Summary of information about Minnesota wolves that traveled long
distances from their pack territories |
Collar
type |
Wolf
number |
Wolf
gender |
Travel
period |
Farthest
point (km) |
Minimum
distance
traveled (km) |
Number of
travel
locations |
Number of
highway
crossings* |
Fate of animal
|
|
VHF
|
2480 |
M |
73/5/17-73/6/30 |
183 |
490 |
14 |
1 |
Unknown while traveling |
|
GPS
|
5399 |
M |
98/5/31-98/7/27 |
185 |
566 |
308 |
17 |
Unknown after return |
|
Satellite
|
7803 |
M |
98/9/12-98/11/12 |
118 |
1054 |
55 |
33 |
Killed during travel |
|
Satellite
|
7804 |
F |
99/3/26-99/9/21 |
494 |
4251 |
274 |
215 |
Killed during travel |
| * State, provincial or
interstate highway only |
Studies reviewed by Fuller (1989) report high, human-caused, wolf mortality
rates. Much of this mortality was from motor vehicles, suggesting that roads can
hinder wolf travel. In our study, however, collared wolves safely crossed major
highways. Three of the four wolves studied (7803, 7804 and 5399) crossed
numerous interstate highways and many more smaller roads during their travels.
This behavior supports findings that wolves in the Midwest are rapidly adapting
to human presence (Thiel et al., 1998). The fourth wolf (2480) traveled
mostly through wilderness, likely encountering few human structures.
Nevertheless, the long distances the other wolves traveled through mostly
human-dominated landscapes illustrate that few structures or landscape features
could be considered travel barriers for these wolves. Roads will continue to
pose risks to any wolves crossing them, but their function as travel barriers is
perhaps more a question of probability than of permeability.
Acknowledgments
Support for this project was provided by the Minnesota
Department of Military Affairs; Minnesota Department of Natural Resources; the
Special Projects Foundation, Minneapolis; the U.S. Geological Survey; the U.S.
Department of Agriculture North Central Research Station; and the Prairie Wind
Middle School Eyes on Wildlife Program. We also appreciate field assistance of
W. E. Berg, J. Brezinka, B. Brown, S. H. Fritts, M. Skoglund, P. Watt and P.
Wolf and GIS support from C. Erickson and G. Swenson.
Literature Cited
BALLARD, W. B., R. FARNELL and R. O. STEPHENSON. 1983. Long
distance movement
by gray wolves, Canis lupus. Can. Field-Nat,
97:333.
BALLARD, W. B., D. J. REED, S. G. FANCY and P. R. KRAUSMAN. 1995.
Accuracy,
precision, and performance of satellite telemetry for
monitoring wolf
movements, p. 461-467. In: L. N. Carbyn, S. H.
Fritts and D. R. Seip
(eds.). Ecology and conservation of wolves in a
changing world. Canadian
Circumpolar Institute, Edmonton, Alberta, Occ. Publ.
35.
BERG, W. E. and D. W. KUEHN. 1982. Ecology of wolves in northcentral
Minnesota,
p. 4-11. In: F. H. Harrington and P. C. Paquet
(eds.). Wolves of the world:
Perspectives of behavior, ecology and conservation.
Noyes Pub., Park
Ridge, New Jersey. 474 p.
FANCY, S. G., L. F. PANK, D. C. DOUGLAS, C. H. CURBY, G. W. GARNER, S. C.
AMSTRUP and W. L. REGELIN. 1988. Satellite telemetry: a
new tool for
wildlife research and management. U.S. Fish and Wildl.
Serv. Resour. Publ.
No. 172. 54 p.
FRITTS, S. H. 1983. Record dispersal by a wolf from Minnesota. J. Mammal.,
64:166-167.
_____, and L. D. MECH. 1981. Dynamics, movements, and feeding ecology of a
newly protected wolf population in northwestern
Minnesota. Wildlife
Monogr., No. 80:1-79.
FULLER, T. K. 1989. Population dynamics of wolves in North-Central
Minnesota.
Wildlife Monogr., No. 105:1-41.
HOBBS, R. J. 1992. The role of corridors in conservation: Solution or
bandwagon? Trends Ecol. Evol., 7:389-92.
MECH, L. D. 1987. Age, season, and social aspects of wolf dispersal from a
Minnesota pack, p. 55-74. In: B. D. Chepko-Sade
and Z. Halpin (eds.).
Dispersal patterns. University of Chicago Press,
Chicago. 342 p.
_____. 1995. What do we know about wolves and what more do we need to
learn?,
p 537-545. In: L. N. Carbyn, S. H. Fritts and D.
R. Seip (eds.). Ecology and
conservation of wolves in a changing world. Canadian
Circumpolar Institute,
Edmonton, Alberta, Occ. Publ. 35.
_____, and L. D. FRENZEL, JR. 1971. Ecological studies of the timber wolf
in
northeastern Minnesota. USDA For. Serv. Res. Pap.
NC-52. N. Cent. For. Expt.
Sta., St. Paul, Minnesota. 62 p.
_____, K. E. KUNKEL, R. C. CHAPMAN and T. J. KREEGER. 1990. Field testing
of
commercially manufactured capture collars on
white-tailed deer. J. Wildl.
Manage., 54:297-299.
_____, S. H. FRITTS and D. WAGNER. 1995. Minnesota wolf dispersal to
Wisconsin and Michigan. Am. Midl. Nat.,
133:368-370.
MERRILL, S. B., L. G. ADAMS, M. E. NELSON and L. D. MECH. 1998. Testing
releasable GPS collars on wolves and white-tailed deer.
Wildl. Soc. Bull.,
26:830-835.
MESSIER, F. 1985. Solitary living and extra-territorial movements of wolves
in
relation to social status and prey abundance. Can.
J. Zool., 63:239-245.
THIEL, R. P., S. B. MERRILL and L. D. MECH. 1998. Tolerance of denning
wolves,
Canis lupus, to human disturbance. Can.
Field-Nat., 112:340-342.
WYDEVEN, A. P., R. N. SCHULTZ and R. P. THIEL. 1995. Monitoring of a gray
wolf
(Canis lupus) population in Wisconsin,
1979-1991, p 147-156. In: L. N.
Carbyn, S. H. Fritts and D. R Seip (eds.). Ecology and
conservation of
wolves in a changing world. Canadian Circumpolar
Institute, Edmonton,
Alberta, Occ. Publ. 35.
______
* Merrill, Samuel B., and L. David Mech. 2000.
Details of extensive movements
by Minnesota wolves (Canis lupus). American
Midland Naturalist
144(2):428-433. Jamestown, ND: Northern Prairie
Wildlife Research Center
8711 37th St. S.E., Jamestown, North Dakota, 58401.
Home Page. See at < http://www.npwrc.usgs.gov/resource/2000/
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