Mating System

The yellow-bellied marmot lives in a permanent polygynous harem. The mating/nesting territory is defended by the male. Males compete for territories, making this a case of resource defense polygyny. There is some debate in the literature as to whether or not reproductive success is lower in exterior/satellite populations as compared to the central burrows, but the bulk of it suggests that central burrows promote reproductive success. Armitage and Schwartz performed a well-run, long term study and found that reproductive success is in fact higher in central burrows. This is due to several factors including: continued presence of the dominant male, larger number of females to reproduce, presence of female yearling helpers, and larger matrilines. These reasons influence why a male would want possession of a central burrow (Armitage 2000).

There are also environmental factors that influence reproductive rates. The amount and quality of spring food, and availability of spring hibernacula, influence the reproductive success of populations (Colorado Div. of Wildlife [online] 2001). Yellow-bellied marmots are capable of bearing offspring annually, but often skip a year. Barash (1974) found that yellow-bellied marmots living at higher altitudes behave more like their relatives, the Olympic marmot, who normally live at that elevation. Barash concluded that the differences in the social behavior of various marmot species correlates with the harshness of their environments (Barash 1974).

Mating occurs after emmergence from hibernation in May. Males and females reach sexual maturity in their second year. There is a 30 day gestations period and young are generally born in June. Average litter size is aout 4 pups; half of which survive the first year. Following birth, the litter usually remains in the burrow for about one month before emerging above ground (Armitage 1974).

Male/Male and Female/Female Relationships

Males mainly compete for the burrow site. Within a colony of marmots there is the alpha male and his harem, surrounded by a dominance heirarchy of peripheral males waiting to try and take over the nesting site. Dominant males defend their territory against incursions by peripheral or transient males. Dominant males use scent marking as an expression of their dominance. Actual fighting between males is rare. Most male territory turnovers occur because the alpha male passes away, and the top peripheral male takes over.

The marmot females are kin and possess fairly strong bonds. The younger females will often assist the breeding females in raising the young. This reveals the cooperative behavior between females within the same matriline. There is some agonistic behavior within matrilines, however, expressed by sexual respression of daughters by their mothers (Armitage & Schwartz 2000). Between matriline interactions possess little, if any, cooperation. Between matriline competition consists of infanticide, agonistic behavior and reproductive suppression. The only possible cooperative behavior that may be exhibited between matrilines is alarm calling that may benefit all in the colony (Armitage & Schwartz 2000).

In summation, factors affecting rates of social behavior are related to population density, the use of space, age-sex structure of the population, individual characteristics of population inhabitants, and the number of years the residents have lived together (Armitage 1977).

Parent/Offspring Relationships

Females are the primary caretakers for their young. The recently birted marmots usually remain underground for a month before emerging. Young males usually disperse as yearlings to attempt to claim their own territory. The alpha male becomes aggressive toward young males, an event that also causes them to disperse. Female young, on the other hand, remain in the burrow and become additional mates of the alpha male. This leads to a high degree of relatedness among females. The yearling females are often "helpers" in raising young.

Yellow-bellied marmots are considered moderately social and sociality among young occurred with all members of the matriline, but intermingling with other litters is rare. The cohesive behaviors between mother and offspring of marmots probably influences how social groups are established as well as indicating the amount of post-weaning parental investment (Rayor 1991).