Wolf World Item # 502
Category: Ecology & Behavior
Natural History (February 1987) 4 pp.
A two-year study by the author supports his theory that howling plays a role in maintaining pack territories. Packs were more likely to respond to his howls when they were at fresh kill sites, rendezvous sites, and during mating season. Pack size also apparently influences a pack's decision to reply.
Wild World of Wolves
The Man Who Cries Wolf
Fred H. Harrington
An ethologist decodes the meaning of wolf cries and silences
The winter night was perfect for howling. The air was cold and motionless. Light, fluffy snow blanketed the ground, cushioning my steps as I edged closer to the wolf pack. Best of all, a full moon hung in the clear black sky, illuminating my way and perhaps stirring a few primordial howls within the wolves. Soon I came across wolf tracks that crossed the road and headed toward a spruce bog. I tried to follow, but at every third step I broke through the crust and was left floundering midthigh in powdery snow. I stopped trying to walk, set my microphone on its tripod, and switched on my tape recorder. Then I howled.
Within seconds, a pack of radio-collared wolves answered. For nearly a minute the spruce woods reverberated with a cacophony of yips, yaps and yowls, anchored by an occasional low bass note. Finally, the wolves' reply ended with a series of staccato, barklike yaps.
At the time, I was studying timber wolf howling in Superior National Forest in northeastern Minnesota. Working in conjunction with L. David Mech, of the U.S. Fish and Wildlife Service, I was trying to test a theory that howling plays a role in the establishment and maintenance of wolf pack territories. Each night I searched a vast network of logging roads from an antenna-equipped truck, patiently listening for radio signals from wolves Dave had radio-collared.
Populating the forest were about forty packs of wolves, each occupying some twenty-five to one hundred square miles. Under normal conditions, a pack would satisfy all its needs within an area that size -- there would be an adequate number of dens, for example, and sufficient prey throughout the year. Virtually every square mile in the forest was claimed by at least one pack, so at the edges of adjacent territories, a one- or two-mile-wide overlapping strip was shared. If at all possible, these overlapping areas were avoided by neighboring packs and were thus underused compared with the packs' exclusive territories. Lone wolves accordingly found these areas relatively safe and therefore made frequent use of them. And since the packs tended to stay in their own areas, they rarely met one another or even crossed the path of a lone wolf.
Observing all this led me to wonder if wolves communicate to maintain this quiltlike pattern....
Most animal-vocalization studies use playbacks of recorded calls to provoke live responses. My studies had started that way, too. Using several different taped howls, I had attempted playbacks but had been plagued by poor fidelity and equipment failure....So after three months with no success, I dumped the playback gear and developed my own personal howl.
....I soon developed a standard series of five howls, which I used for the rest of the study. By this time I...had not heard a single wolf howl. Soon, however, the wolves began to reply to me, and when I left the forest two years later, nearly five hundred of my howls had evoked some sort of vocal reply....
A pack's responses, I learned, could be divided into two major categories based on their howling. If a pack responded by howling, it nearly always stood its ground. (Only 3 percent of the time did the pack reply and then retreat.) If it kept quiet, it either stayed put or it fled. Thus, if there is a message to a pack's reply, it probably reads, "We are a wolf pack, we are here, and we intend to stay here." Implicit in this message is the threat that "if you get closer, we might attack."
....When a pack did not reply, it retreated about a third of the time. These retreats ranged from a fraction of a mile to more than a mile. Dave Mech and I watched one small retreat in progress. I was on the ground, howling to a pack about a mile away, while Dave watched from a circling aircraft as the pack rested on a frozen lake. When I howled, one wolf leaped up and appeared to bark once or twice, perhaps to arouse the rest of the pack. Within minutes the wolves retreated from the open ice and into the woods north of the lake, where they lay down again, less than a mile from shore. Now that the wolves knew my location, and had placed a lake between us, they would have ample warning if I moved closer....
Howling thus serves the pack as a long-distance defense system. Wolves may be able to hear howls from as far away as five miles, making them aware of one another's locations long before an accidental encounter can take place. Once aware of a neighboring pack's position, a pack can avoid traveling into an area where a chance meeting would be likely....
When a pack does reply, it may "hope" the intruder will go away. But that doesn't always happen. On an increasing number of occasions, both Dave Mech in Minnesota and researchers elsewhere have watched packs leave their territories and invade those of their neighbors. In some cases, the intruders seemed content merely to filch a deer or moose, eat it hurriedly, and return to their own territory. But other intrusions were different. The invading packs picked up the residents' trail and excitedly followed it, not repelled by the residents' scent, as might normally be expected. In several cases in Minnesota, the intruders pressed on until they had located the residents and attacked them. Most of these incursions resulted in at least one mortally wounded resident. What motivated these attacks is unknown....
If replying to intruders carries the risk of attack, the wolves should expect to reap benefits that make the risk worth taking. One such benefit is the advantage of staying put. For the most part, wolves have no overriding reason to stay put. They can afford to get up, move off, and start hunting again, rather than risk an attack. But if a site contains an important resource, such as their favorite prey or their pups, there is no incentive to move.
Just one of the large ungulates that wolves hunt in Minnesota can keep the average pack well fed for a few days to a week or more. The typical wolf needs about four to eight pounds of meat each day to survive. An adult male moose provides about 725 pounds of edible meat, enough to fuel a pack of six wolves for two to four weeks. Packs are understandably reluctant to leave their kills....
Pups also tie a pack to a specific site, but for a much longer period. Once out of the den at three to four weeks of age, the pups spend the next three to four months at rendezvous sites, where they can grow and mature as rapidly as the adults can keep them supplied with food....Should danger threaten while the pups are near the den, they can scamper back into it and take refuge. But most rendezvous sites lack such havens and the pups are more exposed to danger, making them more dependent on protection by the adults.
Packs are therefore quite vocal at rendezvous sites. For each pack I studied, the highest reply rates were obtained at rendezvous sites during the summer....
As their pups grew and developed, however, packs became less and less responsive. Sometime in late November or early December, by which time pups had been traveling with the adults for some two months, packs were unlikely to reply unless they were camped at a kill....If a pack had just made a kill, I could expect a day or two of replies before the pack clammed up. But I soon discovered that more than kills or pups influenced a pack's decision about replying.
When the breeding season approached in late February, reply rates went up for all my study packs: kills at that time made no difference in responses. With the increased production of reproductive hormones at the onset of the breeding season, there is a parallel rise in aggressiveness. Within the pack, wolves of the same sex jealously compete for the privilege of mating. This agression is directed toward strangers as well. Most fatality-producing encounters between packs occur during the mating season, when the dominant wolves seem unwilling to tolerate a threat to their status from any corner. But the breeding season ends more suddenly than it begins, and as aggressiveness wanes, the number of replies to howling plummets. By April, a month after mating activity had ceased, replies were extremely difficult to elicit.
One last factor seemed to influence a pack's decision whether to reply -- its size. One pack of seven to twelve wolves replied twice as frequently as a smaller pack with four to six members. This was true at kill sites, around rendezvous sites, and elsewhere in the packs' territories....
Such group support seems to make larger packs more aggressive than smaller ones. They are accordingly more likely to trespass into neighboring territories, to attack their neighbors, and to chase away any strangers they encounter in their own territories....
In my two years of howling I had some close encounters with wolves and experienced moments of fear when the mythology about the animals took over and my imagination got the better of me. But only on seven of more than four hundred occasions did a single wolf leave the pack and approach me. Even these approaches happened only when I continued to howl after the wolves had given me one or more vocal indications of their original position.
Another thing. Even after teasing apart my data in as many ways as I could, I was never able to make any connection between wolf howls and the phases of the moon....