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The Usefulness of GPS Telemetry to Study Wolf Circadian and Social Activity


This study supports other reports that wolves are primarily nocturnal (Murie 1944, Mech 1970, Kunkel et al. 1991). A few studies (Kolenosky and Johnston 1967, Vilà et al. 1995, Ciucci et al. 1997, Theuerkauf et al. 2003) examined wolf activity in enough detail to detect increases in activity at dawn and dusk. Our study supports these findings and demonstrates that these peaks may not be detectable via GPS telemetry if the GPS interval is >3 hours. Peaks were lost for wolf 850 during conversion to one location per 4 hours. This suggests that movement patterns with crepuscular peaks may have been present but undetected in several previous studies and may be more common among wolves than is generally known. Observations of some captive wolves (MacDonald 1980) but not others (Kreeger et al. 1996) support this possibility.

One study seems to conflict with our results that wolves are primarily nocturnal. Theuerkauf et al. (2003) concluded that wolves were active throughout the day. However, the apparent difference probably results from our defining activity as actual distance traveled. The wolves in Theuerkauf et al's. (2003) study also traveled least during daylight, so in that respect our findings are in agreement. Apparently, wolves are active during the day without generally traveling as far as they do at night. And certainly in some areas wolves travel extensively during the day (Mech 1966, 1992, Peterson 1977, Peterson et al. 1984, Boitani 1986).

Deer density in our study area was high (G. DelGiudice, Minnesota Department of Natural Resources, unpublished data), so these wolves may have been able to sustain themselves with less time spent traveling during the day, as has also been suggested for reduced wolf movements in Spain (Vilà et al. 1995). Additionally, wolves in our study area coexisted with high levels of human activity (Merrill 1996, Thiel et al. 1998) and high road density (Merrill 2000). Reducing daytime activity may have been a strategy to avoid encountering humans, although this possibility was ruled out in a study in Poland (Theuerkauf et al. 2003).

For the only adult wolf we studied with hourly GPS data, mean minimum rates of travel estimated for all 24 hour periods together (0.58 km per hour) or for only the most active hours between dusk and dawn (0.94 km per hour) do not compare well with rates actually measured elsewhere (8 km per hour; Mech 1970, 1994). Our breeding female's travel rate, when estimated with one location per 4 hours, was 19% lower than when estimated with her complete data set (one location per hour). This confirms the logic that the larger the GPS interval, the more the data underestimate wolf travel rates. Even hourly locations obviously underestimate wolf speed, except when the wolf is traveling for prolonged periods in a straight line.

Male wolf 399

Global Positioning System data from this wolf show a change in his circadian movement pattern associated with his extraterritorial foray. His nearly complete cessation of visits to the den one week prior to the extraterritorial foray suggests that he ceased participating in pup rearing prior to his departure. Upon commencing the extraterritorial foray, wolf 399 began traveling during the day rather than at night. This shift represents an unusual example of a mammal altering its circadian rhythm in accordance with something other than seasonality or day length. Although there are examples of wolves altering their circadian rhythms during denning (Vilà et al. 1995,Theuerkauf et al. 2003) and of other animals during estrus (Cushing and Cawthorn 1996) and in response to different social stimuli (Regal and Connolly 1979, Mrososovsky 1988), we found no other reports of animals changing circadian movement patterns during travel away from a natal territory.

Traveling primarily during daylight might have had 2 important benefits for the traveling wolf. First, the animal may have used detailed visual cues to navigate and be able to return to his natal territory using the same general route. This hypothesis was supported by the closeness of the inbound and outbound travel ways followed by the wolf (Figure 2), which also suggested the wolf might have had a complex memory of landscape features. The visual system of canids is best adapted for crepuscular and daytime activity (Kavanau and Ramos 1975, Roper and Ryon 1977). Second, the wolf probably traveled through several other wolf territories during the extraterritorial foray. Because these other wolves were probably primarily nocturnal, traveling during daylight may have reduced the likelihood of agonistic conspecific encounters. However, daylight travel probably increased chances of negative encounters with humans. Development of nocturnal patterns as a means of avoiding contact with humans has been suggested for European swine (Sus scrofa; Briedermann 1971) and the Nile crocodile (Crocodllus nilotzcus; Corbet 1961), although not for wolves (Theuerkauf et al. 2003). A nocturnal pattern during the extraterritorial foray would have been expected if the wolf had been avoiding human contact; the diurnal pattern suggests it was not.

Dispersing wolves in some areas show significantly lower survival rates than wolves of the same age that remain in packs (Peterson et al. 1984, Messier 1985). In one study 90% (18/20) of mortalities among dispersing wolves resulted from human causes (Boyd and Pletscher 1999).

Although the diurnal pattern for our wolf cannot necessarily be extrapolated to other wolves, possibly other wolves disperse or travel on extraterritorial forays more during the day. If so, this could be maladaptive in human dominated landscapes and could have contributed to the high dispersal mortality reported by Boyd and Pletscher (1999).

Breeding female wolf 850

Location data obtained from this wolf parallel changes in her life history stage as well. When she produced pups, her movement pattern changed from nomadism within a territory with no obvious center of activity to making numerous trips away from her den. This spoke like pattern of movement away from a center of activity supports previous observations (Zimen 1978, Ciucci et al. 1997, Mech et al. 1998). Data collected during the second 6 weeks after denning demonstrate the ability to identify rendezvous sites using GPS telemetry data.

The nocturnal pattern of 850's trips away from the den is consistent with most studies (Murie 1944, Kolenosky and Johnston 1967, Haber 1977, Ballard et al. 1991,Williams and Heard 1991, Mech and Merrill 1998, Theuerkauf et al. 2003). The exceptions are Chapman (1977) and Harrington and Mech (1982), who found that breeding wolves left the den most often in the morning. Harrington and Mech (1982) suggested that their observations were related to cooler daytime temperatures in Minnesota, permitting wolves to be more active during daylight, and to the fact that Minnesota's latitude provides longer periods of twilight for wolves to hunt when their prey are most active. However, our study also occurred in Minnesota, with the same temperature regime as Harrington and Mech's (1982) study, and wolves tend to depart from dens at about the same time daily regardless of latitude (Mech and Merrill 1998). The results of Harrington and Mech (1982) therefore remain unexplained.

The small number of wolf 850's locations away from the den during the 6 weeks after she produced pups is similar to reports in other studies (Harrington and Mech 1982, Ballard et al. 1991,Vilà et al. 1995, Jedrzewski et al. 2001). When wolf 850 left her den, she still traveled substantial distances and apparently patrolled her territory boundary (compared with GPS locations near the perimeter of her boundary before denning; Figure 6).

Only 2 other studies (Vilà et al. 1995 and Theuerkauf et al. 2003) examined activity patterns of nursing wolves. In the first study, 2 female wolves were nocturnal throughout the year but diurnal for a 6-week nursing period. In the second study, 5 nursing females tended to reduce their nocturnal activity but not their crepuscular activity. Nursing wolf 850 maintained her nocturnal pattern through the 6-week nursing period.

Social aspects of wolf activities

Data collected from breeding female 850, male yearling 840, and pups 820 and 860 demonstrate the usefulness of GPS telemetry data in determining when members of a social group travel together and apart. When the pups were 10 months old, their mother had suspended visiting them. Presumably other pack members had helped provide food, for the pups remained at the rendezvous site most of the time and hunted little themselves.

Different GPS intervals for collars worn by different animals could have obscured some patterns. This possibility was reflected visually in the easternmost of the 3 trips taken by the pups (Figure 8; trip 3 in Table3). Although it appears one pup traveled directly back to the rendezvous site while the other took a more circuitous route (traveling in a clockwise loop), GPS locations at the next place their observed paths overlap were collected within one minute of each other. This information suggested that their paths probably did not split but that the apparent difference in travel routes probably reflected the difference in GPS intervals for which their collars were set.

The approach we used also could be valuable in studies of interspecific competition-for example, between wolves and coyotes (Canis latrans, Peterson 1995) provided that GPS collars light enough for coyotes were used. In addition to examining plots of animal locations on a map, however, dates and times must be carefully compared; what appear to be splits and joins may simply reflect differences in programmed GPS intervals or in GPS location success rate. Nevertheless, GPS telemetry data represent a useful new approach to studying wildlife activity patterns.

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