Dr. Kerry Foresman
Intraspecific Communication and Pack Behavior of the Gray Wolf (Canis Lupus)
*Reese C. Morrison, College of Forestry and Conservation, University of Montana, Missoula, MT 59812 USA
Joshua W. Wilkerson, College of Forestry and Conservation, University of Montana, Missoula, MT 59812 USA
Aaron Little, Division of Biological Sciences, University of Montana, Missoula, MT 59812 USA
*Correspondence: [email protected]
Complex social behavior is widespread among the animal kingdom. Group membership potentially allows each member to increase their overall survival and reproductive rates, above what one would acquire from a solitary life (Wilson, 2000). The Wolf (Canis lupus) is a social animal, and is no exception. Much of a wolf’s livelihood is dependent upon the pack working as whole (Mech 1970). This is achieved by an intricate system of communication. Group formation necessitates a certain degree of sociality, as members quite often have different conflicts of interest (Cordoni and Palagi 2008). “Peace-keeping” seems to be a primary function of social behavior (Fatjó et al, 2006, Cordoni and Palagi 2008). Successful communication between conspecifics greatly reduces territorial conflicts and physical injury (Harrington and Mech 1979, Cordoni and Palagi 2008, Sands and Creel 2004). Communication also facilitates access to food and other resources throughout the landscape (Mech 1970). This complex social system allows this species to thrive as an apex predator. However, this success has historically been compromised by another predatory social species, mankind.
Pack sizes usually range from five to fifteen members, and are formed when individuals disperse from their parental packs and raise a litter of their own (Wilson 2000, Asa and Valdespino 1998). Packs are usually a group of extended relatives (Sands and Creel 2004, Wilson 2000), consisting of a monogamous Alpha pair and their subordinate relatives (or “auxiliary” pack members). Wolves are cooperative breeders, with high parental investments from the Alpha male and female and auxiliary wolves (Peterson et al. 2002, Harrington et al. 1983). Alpha males have been observed feeding, defending, guarding and playing with their offspring. Such a high degree of paternal care is a relatively rare occurrence among mammals (Wilson 2000). This group coordination towards raising the young is an example of kin-selection. Extended relatives help care for their younger siblings/cousins, and in turn propagate some of their own genes into the next generation (Harrington et al. 1983). This occurs despite the lack of direct descent. Auxiliary wolves do not participate in any reproduction due to behavioral suppression by the Alpha pair (Asa and Veldespino 1998). However, there can be some confidence of direct relation. The monogamous behavior of the Alpha pair helps to ensure a certain degree of relatedness between the young pups and the auxiliary wolves that help care for it (Asa and Valdespino 1998). It would appear that the benefits of cooperating with the group include an increase in indirect reproductive output.
Even though there are obvious benefits of social aggregation, lone wolves are common. These individuals exhibit few typical social behaviors found in their social counterparts, such as howling or scent marking (Harrington and Mech 1979, Cordoni and Palagi 2008). Packs are known to reject lone wolves that attempt to join the pack (Cordoni and Palagi 2008). One observational study witnessed amplified aggression towards outcast (or “pariah”) wolves (Cordoni and Palagi 2008). However, genetic evidence has suggested that occasionally lone wolves are incorporated into an existing pack (Asa and Valdespino 1998). This is most likely a necessary condition to facilitate adequate gene flow between populations.
Dominance and Leadership
The wolves’ social hierarchy is held in place by a complex system of dominant and subordinate rituals (Fatjó et al. 2006, Wilson 2000) The available research implies that visual signals are the most predominant method by which wolves communicate with other pack members. While these encounters are intricate and subtle displays of body language and facial expressions, there are a few key behaviors that can help indicate a wolves’ status during an interaction. Subordination is communicated for example via lip licking, flattened or lowered tail and ears, and retracted lips (Fatjó et al, 2006). Dominance can be expressed through a confident and erect body posture, ears and tail (Fatjó et al, 2006).
Wolf pups take some time to develop these social skills. Juvenile wolves initially begin to form dominance relationships by play fighting (Wilson 2000). Dominance relationships among the pups remain very unstable as the young begin social development (Macdonald 1973). Macdonald (1973) examined personality development in an all male litter of wolf pups. In a laboratory environment, he observed reactions to unfamiliar objects; initiative young (those that went first to investigate the object) were classified as “leaders.” At around 44 days, a pup established a leadership that remained relatively constant for the duration of the study. In the wild, young pups are incorporated into the pack hierarchy at around six months of age (Mech 1970). Fine-tuning of social skills in juvenile wolves is not achieved until two or three years of age (Harrier and Mech 1979).
Peterson et al. (2002) observed leadership behavior in three packs of wolves from the Yellowstone area. In this study, pack leaders are defined as those that initiate activities of the pack (Peterson et al. 2002). Activities include rousing the pack from rest, moving after greeting ceremonies (wolves lick and smell the mouths of one another after being separated for some time (Wilson 2000)), chasing prey, changing the course of pack movement, and defending the pack from foreign wolves. Peterson et al. observed 104 instances of these events, and breeding individuals accounted for 78 of these observations.
There is some dispute about the definition of an alpha male. Dominant individuals have been defined as “wolves that successfully influence the behavior of a subordinate counterpart” (Peterson et al. 2002). Mech (1970) has referred to the dominant male as the individual who guides attacks on invading foreign packs. Wilson (2000) defines dominance as “priority access to food, favored resting places and mates.” Regardless of the multiple definitions, there remains a general understanding that leadership is related to dominance in some form. Ultimately, the dominant individuals are the ones who will reproduce in the next breeding season.
After a physical conflict among pack members, it is common for a neutral bystander to come into physical contact with the victim of the attack (Palagi and Cordoni 2009). There is some dispute about whether or not this behavior is true “consolation.” To avoid anthropomorphism, this behavior has been coined “unsolicited third party contact” (Palagi and Cordoni 2009). The more familiar the victim wolf was with the bystander wolf (indicated by the amount of physical contact observed throughout the study), the more likely it was for the bystander to contact the victim without being solicited (Palagi and Cordoni 2009). This interpersonal behavior has only been observed in primates and wolves. Both have highly complex social structures based on mutualism (Wilson 2000). Unsolicited third party contact is believed to be a behavior by which the pack (as well as in other social species) retains stability, despite individual competition over resources (Palagi and Cordoni 2009).
There are two primary ways in which wolves communicate territorial boundaries: scent marking and howling. Scent marks are long-term and specific to the area marked, and howling is immediate and is observed for miles (Peterson et al. 2002, Tooze 1990). Territories can range from 166 km2 to 1000 km2 (Karlsson et al. 2007). While occasionally wolves will meet and fight over boundary lines, there can be significant spatio-temporal overlap of territories (Wilson 2000). These types of intraspecific competition help to minimize physical conflict between packs (Peterson et al. 2002, Tooze 1990).
Generally, the dominant breeding pair does most of the scent marking. Peterson et al. (2002) logged 499 hours of observation, and witnessed 158 occurrences of scent marking. All but three were made by either the dominant male or female. Non-breeding wolves (including lone wolves) rarely scent mark their territory (Rothman and Mech 1979).
Harrington and Mech (1979) studied the howling behavior of eight packs and ten lone wolves in Northeastern Minnesota. This two-year long experimental study measured the rate at which wolves reply to human howls. Larger packs had higher response rates than smaller packs. Lone “pariah” wolves never replied to a human howl. Alpha males (separated from their respective packs) occasionally approached the direction of the howl, while most other adults retreated. Younger wolves tended to reply more often than their older counterparts until they were about two years of age (Harrier and Mech 1979). Around kill sites, the reply rate increased with increasing size of the carcass. Reply rates are higher during late autumn and mid-winter. The sooner the pups developed in August, the sooner reply rates declined. The mid-winter increase corresponds with increased mating behavior (i.e. copulation) (Harrier and Mech 1979). These are all vital resources that require defense against conspecific competitors (Harrier and Mech 1979). All of these patterns indicate howling plays a major role in yearlong territory maintenance (Harrier and Mech 1979).
If the conditions are right, a lone wolf has a relatively high chance of killing its prey. In example, a single wolf can easily outmaneuver a healthy sheep if the chase is downhill (Wilson 2000). However, while a single wolf can successfully take down an animal, it will have a much greater chance of success if it cooperates with other wolves to maneuver the animal into a favorable situation. When wolves hunt together, they do so as a single cooperative unit (Wilson 2000). Depending on the prey, wolves may hunt in groups of two to ten or more individuals (Wilson 2000). Multiple researchers have observed wolves driving caribou (Rangifer taurandus) towards waiting members of the pack (Wilson 2000). Pack hunting permits these animals to take down larger and more difficult prey by coordinating each other’s movements (Mech 1970). However, most hunts end unsuccessfully. Mech (1970) observed 131 moose hunts in Isle Royal National Park, in 54 instances the wolves could not get within 20 meters. Only six of the 131 encounters resulted in a kill (Mech 1970).
Stress in Packs
Stress levels can be measured with fecal glutocorticoid (GC) levels. GCs are secreted by the adrenal cortex when an animal is placed under stress. This prioritizes the distribution of ATP, slowing the body’s “peripheral” processes (i.e. digestion, growth and reproduction) in favor of immediate physiological requirements (C. Breuner, Personal Communication, March 2009). Earlier studies on social stress in wolves done in the 1950’s indicated that subordinate individuals have higher levels of stress (Davis and Christian 1957). It was believed that dominant individuals physiologically suppressed of the subordinates reproduction system. Today, most evidence suggests this is a behavioral phenomenon (Asa and Valdespino 1998). In 2001, it was determined that fecal GC levels are highest in the dominant individuals (Creel 2001). However, GC levels appear to have no correlation with rank below that of the alpha members. Neither temporary change in climate nor aggressive/agnostic behaviors had a substantial influence on GC levels. Increased GC levels corresponded with an increase of aggressive interactions for a short period during the mating season (Sands and Creel 2003). Contrary to Creel’s findings, McLeod, et al. (1995) observed the highest urinary GC levels in a beta male. This particular beta male had a high occurrence of aggressive encounters. In one wild pack, Creel (2001) witnessed the lowest-ranking female and the alpha female involved in almost the same amount of breeding behavior. In that year, three female wolves produced litters. Low status does not result in complete infertility (Packard et al. 1983), but may possibly contribute to decreased reproductive potential.
Overall, it would appear that that GC levels are most closely related to the stability of a wolves’ rank. Aggressive, status-seeking wolves are subject to higher stress levels (Packard et al. 1983). It has also been suggested that differences in reproductive status may account for differences in GC levels (Sands and Creel 2004). This would account for the increased levels of GC during the mating period.
Wolves have extremely complex social lives that begin shortly after birth. Wolf young require a great amount of parental investment in order to participate within the social structure. Like most complex social systems, there is period of social maturation in which the young are taught proper social behavior within the family unit (Wilson 2000). A pup may learn to be subordinate, and help raise the young of the alpha pair. Or, the pup may learn to be dominant within the group, and eventually become the reproductive "Alpha" wolf.
There are indeed disadvantages to being a subordinate in pack life. These individuals rarely mate, they have little priority over food and other resources, and they are subject to aggressive dominant behaviors. However, there is something to gain from this altruistic behavior. Sociality has provided wolves with an enormously powerful method of survival and reproduction. Group behavior facilitates the gathering of food, the security of resources and reproductive opportunities, and the continued persistence of the species.
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