Determining rank by observation and experimentation.
By Ian Dunbar, PH.D., M.R.C.V.S.
Source: GAZETTE, Behavior, pp 36 & 38.
As part of Dr. Frank Beach's long‑term study of the behavioral endocrinology of sexually differentiated behaviors in dogs (conducted at the University of California, Berkeley), he investigated sex differences in social rank and aggressiveness.* His findings proved so rewarding that observational experiments on the development of social hierarchies in dogs became the focus of the research program for nearly a decade.
Social rank was assigned primarily from results of dyadic bone tests (two dogs with one bone), and from general observations of the pack at large, Standard dyadic bone tests comprised two parts: first, the equal opportunity test. In which a bone was thrown to land equidistant between two dogs and the ensuing interactions (possession, approach, threats, etc.) were observed for 90 seconds: and second, the affirmative action test, wherein the bone was given to the underdog for 30 seconds and then the higher ranking dog was released from a holding cage and their interactions were observed for a further 90 seconds.
Male‑Male Dyads. An examination of intermale relationships demonstrated a linear hierarchy with extremely infrequent variation in nearly ten years of testing. Ownership of a bone‑‑or any valued commodity‑‑was almost always decided by the rank of the dogs concerned, regardless of the specific situation.
Female‑Female Dyads. Females had a similar linear hierarchy, but compared with males they exhibited more variation from day to day, Female success was often dependent on the specific situation, For example, if both females had an equal opportunity to take possession of the bone, its ownership was decided primarily by rank, However, if a bitch had established possession, it was not uncommon for her to defend the bone against higher ranking females and sometimes against higher ranking males.
Male‑Female Dyads. In view of their greater size and strength, it was not surprising to find that males were generally higher ranking than females and won nearly 80 percent of the tests.
Group Structure. Males and females had separate hierarchies: an almost fixed linear hierarchy for males, and a more flexible linear hierarchy for females. Within the group as a whole, the rank order of males was always the same and the order of females was usually the same, but the relationship between males and females often varied from day to day.
The various dyadic relationships were the building blocks for group structure, though observations of the group as a whole revealed additional variations and complexities, generally favoring lower ranking individuals. For example, when the bone was thrown to a group of twenty dogs, opportunistic lower ranking animals would often get a few bites of meat before a higher ranking dog expropriated the bone.
At one interesting point in the study, immediately after the top dog Ken had died of old age, the rank of the next top five dogs showed a perfect inverse correlation with regard to body weight: The top dog, "Fast" Eddie, was the smallest: the number two dog, Cassius, was the second smallest: middle ranking Joe was the midsized dog; and Whip‑‑the underdog‑‑was the largest in the pack!
When a hungry pup is confronted with an occupied teat, it has a couple of options: to supplant the resident nurser, or to search for an unoccupied teat. An analysis of teat expropriations and teat defenses revealed a rudimentary linear hierarchy as early as two weeks of age. High rank was strongly correlated with body weight: Larger pups were able to supplant others and hence had primary access to the bitch's milk‑‑further increasing their weight advantage. Rank was also correlated with sex: Male pups (often heavier) were usually higher ranking than females.
Intralitter Pup‑Pup Dyads. Dyadic and group bone tests revealed that within each litter both the top dog and the underdog were irrefutably established by eight weeks of age. Top and bottom ranking dogs have unique social positions, since both may generalize about their social relationships. The top dog assumes it is higher ranking than the rest of the pups, and the bottom dog learns that it is lower ranking to all. However, middle order pups experience a more complicated social scenario since they are higher ranking to some individuals but lower ranking to others. The middle order relationships were not firmly established until the pups were 12 weeks of age, whereafter each litter had a stable linear hierarchy, with rank correlating strongly with sex and weight: Male pups and/or heavier pups tended to be higher ranking.
Interlitter Pup‑Pup Dyads. Each litter had grown up with mom in individual indoor/outdoor runs. When three of the litters were 10, 12 and 16 weeks old, they were transferred into a large outdoor living area along with 12 adult dogs (including the sires and dams). Relationships between littermates remained stable. The most important determinants of rank in pups from different letters were age and sex: Older and/or male pups were higher ranking. At this age, even a small difference in age represented a considerable weight advantage.
Pup‑Adult Dyads. One day after testing, we noticed pups competing for a bone in the group enclosure. The top puppy, James, won the bone, whereupon all the other dogs encircled James and watched him chew. Obviously, none of the pups was going to take the bone away, and it seemed like the adult dogs were somehow inhibited from doing so too. After a while, Doris, a low ranking but opportunistic female, inched forward and gently tugged at the bone. James growled. snarled, but eventually gave up the prize. The instant James relinquished possession, the bone rapidly changed paws a number of times, ending up with Eddie, the top dog.
The above incident prompted a two‑year series of bone tests between adults and pups (from these and other litters). In the equal opportunity test, adult dogs always captured the bone and never let pups come close. However, in the affirmative action test, adult females never took the bone away from two‑month‑old pups, and adult males expropriated the bone in only 40 percent of the tests. By the time the pups were six months old, adult females expropriated the bone in 60 percent of tests and adult males always took it away. It was apparent that adult dogs, bitches especially, showed leniency towards pups in social situations.
The termination of this "puppy license" is cued by rising testosterone levels in male pups at four to five months of age, reaching a peak at around 10 months before declining to stable adult levels. When puppies approached adolescence, they were continually harassed by adult dogs, male adolescents by adult males especially. This stressful phase of social development is short, because the pups quickly learn to display active and exaggerated appeasement to allay adult harassment.
Relative size and strength is the most important determinant of rank at each stage in development. However, once pups of the same breed have grown up and assumed their relative positions within an established adult hierarchy, there need be no correlation between rank and adult weight. Social hierarchies must always be viewed in a developmental context. Indeed, the above mentioned adult male hierarchy that was negatively correlated with adult weight had, in fact, a perfect positive correlation with age. Thus, although in adulthood Cassius was larger than Eddie, for the first six months of Cassius' life he was a mere slip of a pup compared with a three‑year‑old and very macho Eddie.
*Competitive Behavior in Male, Female, and Pseudohermaphroditic Female Dogs by F. Beach, M. Buehler and I. Dunbar. Journal of Comparative and Physiological Psychology, 1982.