Part of a typical maturation journey for young wolves is setting off in search of a mate, leaving behind the natal pack, to seek their fortunes in new territories among unrelated potential partners. The process of leaving home is called dispersing, and it generally happens in a wolf’s second or third year, notes International Wolf Center founder Dr. L. David Mech. He calls a natal pack a “dispersal pump” that regularly sends out both male and female offspring so that mainly the youngest pups and those from the previous year remain. Depending on the wolf involved, dispersing can be accomplished in many ways, with varying degrees of success.
A recent article by Dr. Mech outlines nine such methods he and other biologists have observed; they include remaining in the natal pack’s territory; finding a mate without reproducing and then breaking up to return home; establishing a new pack adjacent to the natal one; and pairing and splitting with new mates serially. Three additional dispersal methods are the topic of further comment in Mech’s paper, “Unexplained patterns of grey wolf Canis lupus natal dispersal,” published last year in Mammal Review, a zoology journal of The Mammal Society.
The three unexplained ways of dispersing are:
1) uni-directional, long-distance travel despite the likelihood of potential mates nearby
2) round-trip travel from natal packs for varying periods and distances, also called extraterritorial movements, and often not resulting in successful pairings
3) coincidental dispersal by individual wolves from the same pack in the same basic direction and over the same distances.
In the first example, dispersing wolves travel on a relatively straight trajectory, as though headed to a specific area they can somehow envision. In many cases, potential mates and prey were known to exist in a wide swath around the natal pack, raising the question of why an animal would leave the area if it weren’t necessary. A key question, Mech notes, is this: How would this straight-line travel be more advantageous in locating a mate and a new territory, compared to following a more random track? The only upsides appear to be increased likelihood of finding genetically unrelated company among more distant wolves and decreased likelihood of competition from dispersing littermates. These factors might offset the risks of not finding a mate at all in the new territory and facing the dangers that lurk for a solo traveler between the home pack and a distant destination.
Another possible explanation, Mech suggests, is that wolves may be able to detect from far away such relevant information as prey density or habitat, or may be influenced by landscape features or other factors that drive them to head in a fairly straight line for a distant place they have never known.
You can go home again
The second type, dubbed round-trip dispersal or extraterritorial movement, involves the wolf leaving home only to return after periods of a few days to as many as 17 months, and traveling as few as 6 km (3.7 miles) to nearly 500 km (more than 310 miles). In these cases, some dispersing wolves succeed in finding a mate, and others do not. Some trips of this type are so short they appear to be exploratory.
In other instances, wolves that take long-term treks over many miles, into areas rich with prey and potential mates, also return to home territory—leaving the question of why they roamed at all.
Researchers have defined “extraterritorial movement” in different ways. For instance, one study described two types of extraterritorial movement, referring to dispersers that remained permanently at least 40 km (nearly 25 miles) from their natal pack, and those that traveled long distances and stayed with various packs over time. Few wolves in that 1995 study returned home.
A study conducted a decade earlier considered any movement of more than 5 km (3.1 miles) from a wolf’s home territory to be an extraterritorial movement, but of 56 such movements observed, 45 wolves returned to the pack in a behavior called a “pre-dispersal trip.” During the intervening decade, other articles referred to these walk-abouts variously as dispersals, pre-dispersal forays and temporary excursions, suggesting various motives of individual wolves.
Mech points out that some earlier studies were based on information from old technology that provided only infrequent location data. Since satellite and GPS collars have been in use, much more detail about these types of trips is known. The longest observed round-trip wolf journey seems to be that of a two-year-old female, 7804, that left her Minnesota home in 1999 and wandered at least 4,251 km (2,641 miles) to a point 494 km (307 miles) away and returned to her natal area—all during a six-month period.
Why go home?
For a dispersing wolf, returning to natal territory almost guarantees competition for food, Mech writes, although “the uncertain nature of a hunting lifestyle and fluctuating food supply makes it likely that a pack’s social dynamics will change frequently.” Therefore, some wolves might leave or be expelled from their natal pack at a time of food scarcity, only to find upon return that there is less competition and more food.
One explanation Mech offers for wolves’ return to home territory is that survival is often better in natal packs, since wolves that remain the longest generally survive the longest (although one study found little difference in survivability between dispersers and those that remained with the natal pack). They may also have the best chance of breeding success. Called biders—as in “biding their time”—such home-body animals can breed if an outsider mate is accepted into the pack.
Mech notes that some dispersers return to their natal pack or territory after a pair-bonding that did not result in successful reproduction. Female wolves may be more likely to return home than males, but whether this is a firm pattern is not yet established, as some studies used samples too small or did not record the sex of the animals observed.
“Haven’t I seen you before?”
The third type of dispersal, called coincidental, is the hardest to explain, Mech says. It refers to members of the natal pack—presumably littermates or possibly siblings from another year’s litter—that head out individually in the same basic direction and travel about the same distance, sometimes meeting up later or finding themselves together with their siblings as new members of an existing pack. This pattern suggests genetic involvement in the dispersal method, although it is not proven, as other litter members have been known to disperse differently. And it appears to fly in the face of the “uni-dimensional travel” theory that traveling a far distance will more likely result in finding unrelated mates.
Mech cites various instances of this third type of dispersal. In one, three members of the Perch Lake pack in northeastern Minnesota dispersed north-eastward over more than 180 km (112 miles) only to end up being killed within 27 km (16.7 miles) of each other. In Montana, it was reported in 1999 that a male and a female from the same pack dispersed nine months apart but were found three years later, 150 km (more than 93 miles) away in the same pack. In another instance, two wolves dispersed a week apart and were found together 170 km (more than 105 miles) away three months later, again in the same pack. In yet another instance, Mech cites two males in north central Minnesota that traveled north separately from the same pack for over 330 km (205 miles) and a few months later were found together. In other studies, wolves in Finland and Sweden showed similar dispersal patterns.
Drilling down in the data on the Perch Lake pack, Mech found more interesting coincidences. From 1982 to 1989, five members, including three from the study referenced above, all dispersed from 182 to 309 km (113 to 192 miles) at compass settings from 56 to 68 degrees, with two ending up 8 km (just under 5 miles) apart, and the other three 27 km (nearly 17 miles) apart from each other. He notes that the proportion of these five (of 18 possible) dispersers heading in directions only 12 degrees apart was significantly different from random dispersal directions.
The Sawbill pack, also in northeast Minnesota, is another example, with four wolves dispersing individually over several years. Two traveled in an arc only four degrees apart from each other to the northwest and were known to end up 11 km (nearly 7 miles) apart. Two other members traveled 180 km (nearly 112 miles) in a 3-degree arc to the northeast and were found to be 8 km (just under 5 miles) apart. In each case, Mech notes, the dispersal direction of each member of each pair was significantly different from random.
This tendency of some wolves from the same pack to disperse to the same area, as well as the propensity of some wolves to disperse many kilometers uni-directionally away from their natal packs rather than floating more haphazardly around the local population, remains unexplained. Conceivably, some dispersers considered at first to be uni-directional float far and wide before ending up far from their packs, thus giving the impression that they traveled in a straight line. The wolves in the Sawbill and Perch packs had seven months to three years to get from their natal pack to their endpoints, and their locations in the interim were unknown. But as radio-tracking technology improved with the development of satellite and GPS equipment, it became clear that some wolves do disperse uni-directionally soon after leaving their packs.
Research on wolf dispersal continues to uncover interesting results—for instance, a 2018 study tested hypotheses concerning the density of humans, bears, prey, land-cover and other factors, and found that wolves dispersing 40 km (24.8 miles) or less settled in areas similar to those in which they were raised, while those traveling farther did not. A 2019 study found that wolf pairs in which the female was born in an area of human influence were unlikely to settle far from humans. Mech hopes studies will continue to focus on dispersal issues, concluding “sooner or later, at least some of the unexplained wolf dispersal patterns will be understood.”
This article was originally published in the Spring 2021 edition of International Wolf magazine, which is published quarterly by the International Wolf Center. The magazine is mailed exclusively to members of the Center.
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Tracy O’Connell is professor emeritus at the University of Wisconsin-River Falls in marketing communications and serves on the Center’s communications and magazine committees.
