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A Classical Territory:

The beaver’s territory, defended by the family, is a habitat with artificial ponds created by dammed rivers and streams.(Col 1998) Sometimes beavers can also be found living in riverbanks in locations that contain swiftly moving water. (Wheatly 1997, Col 1998, Grzimek 1975) The beaver territory is a classical territory. Feeding, mating and nesting all take place within this defended space. (Grzimek, 1975) Territories are often noted to follow shorelines because the shore provides the beaver with their primary food source- aquatic plants growing in shallow water, and nearby terrestrial trees. (Wheatly, 1997) There is no seasonal variation in the size of the territory defended by a beaver colony. The borders remain stable through out the year. (Rosell, 1998) A beaver colony can inhabit the same territory for long periods of time but will move to another territory if their food supply is exhausted (Col, 1998) or when accumulated silt makes the pond habitat too shallow (Jackson 1997).


Social Spacing

Sections: A Classical Territory Who lives in a Colony? Dispersal of the Young The Artificial Habitat Territorial Defense Why a Classical Territory?	A Classical Territory: The beaver’s territory, defended by the family, is a habitat with artificial ponds created by dammed rivers and streams.(Col 1998) Sometimes beavers can also be found living in riverbanks in locations that contain swiftly moving water. (Wheatly 1997, Col 1998, Grzimek 1975) The beaver territory is a classical territory. Feeding, mating and nesting all take place within this defended space. (Grzimek, 1975) Territories are often noted to follow shorelines because the shore provides the beaver with their primary food source- aquatic plants growing in shallow water, and nearby terrestrial trees. (Wheatly, 1997) There is no seasonal variation in the size of the territory defended by a beaver colony. The borders remain stable through out the year. (Rosell, 1998) A beaver colony can inhabit the same territory for long periods of time but will move to another territory if their food supply is exhausted (Col, 1998) or when accumulated silt makes the pond habitat too shallow (Jackson 1997).
Who lives in a Colony? Most beavers live in a kin group called a colony. This kin group consists of the adult breeding pair, the yearlings, and kits from the previous year’s litter. The average family size is 4-5 individuals, although in some cases there can be as many as 13 individuals.(Lixing sun 1988) The colony members live together in either a lodge or a bank den depending on their habitat. Non-family beavers, those that are solitary or unpaired are usually the disperses. They can live alone in an abandoned lodge or bank until they find a mate. (Wheatly, 1997) Dispersal of the Young: Young beavers are driven from the colony at the age of two when they sexually mature. These sub-adults, also known as disperses, leave their family shortly before the new litter arrives. Disperses must find their own territory in which to establish but they rarely travel more than 4-6 Km from their natal colony (Lixing Sun 1988). Since the sub-adults travel such a short distance from their relatives, it is important to be able to recognize relatives from previous litters to avoid inbreeding when choosing a mate . Beavers are able to recognize kin through the mechanism of phenotype matching using the secretions of their Anal Scent Gland (ASG) markings (Lixing Sun 1997). Beavers prefer to colonize rich habitats even if they must move through unsuitable or less suitable habitats before eventually selecting a territory. (Halley, 2002) Beavers that disperse become solitary, non-family beavers that usually live in poor quality habitats while they are attempting to establish themselves and find a mate (Wheatly 1997). These poor quality habitats are normally areas where it is impossible to build a dam (Matz 2003).

The Artificial Habitat:
The beaver has several specific habitat requirements that all center on the need for a constant, still, deep water supply. This water ensures (Cahalane 1947, Grzimek 1975, Jackson 1997, Matz 2003, Walker 1964): 1- that there is necessary vegetation along the water’s edge 2- protection from terrestrial predators 3- an unfrozen aquatic habitat during the winter, and a location where food can be stored as a winter cache 4- a highway along which they can float food and lumber.
		To view a photo of a beaver lodge taken in Beaver County Utah, click below.
In order to guarantee that there is a constant supply of deep water, the beaver is able to create for itself an artificial habitat- A POND! To create this habitat, dams are constructed using sticks, bark, mud, logs and other available material (Col 1998). The whole family contributes in this endeavor. A beaver family is capable of building a 10m-long dam in just under a week (Grzimek 1975). The dam stores up water from slow moving rivers and streams to create a year-round reservoir of water. There are two types of housing typically used by the beaver: the lodge and the bank den. In the middle of the artificial lakes they create, beavers build a lodge, which is a domed house made of twigs, mud and logs (Shepherd 1994). Due to predation pressures from terrestrial carnivores, the entrance and exit of the lodges are below the waterline. (Caras, 1967) Beavers can also build their homes in a bank den, which is dug into the side of a river. Beavers build a house in the riverbank only if the habitat is located on a river too large to be dammed (Grzimek 1975). The bank den is covered with the same material used to build lodges (Cahalane 1947). With either housing style, the bank den or the lodge, the beaver uses their den as a home year round (Shepherd 1994).

Territorial defense: Aggression is rare and is limited to the breeding season. Aggressive encounters can be severe and fatal, especially if the water is contaminated and wounds become infected (Walker 1964, Cahalane 1947). Otherwise, the beaver territory is maintained and defended using scent mounds marked with the secretions of either or both the anal gland secretion (AGS) and castoreum (Rosell 1998). The scent mounds are constructed along the shoreline by piling together mud and debris. Scent mounds are made and marked by both sexes and all age classes except kits younger than 5 months (Rosell 1997). Scent mounds are deposited throughout the year, but the amount of mound construction peaks during the spring (April- May) when dispersal of the sub-adults is the highest (Butler 1979, Rosell 1997). Scent mounds are also noted to be constructed more often in areas of high activity and in situations when there was a high probability of disperses moving through the territory (Butler 1979) . Scent marking for territorial defense is hypothesized to be a cue that allows intruders to associate the territory with residents to reduce the risk of agonistic encounters. It is beneficial to avoid agonistic encounters that may escalate to violence because bite wounds can be deadly. For example, bite wounds from agonistic encounters are the main cause of death in the adult beaver in May, the time disperses are attempting to establish new territories. Another hypothesis that connects territorial defense with scent mounds is that scent marking may serve as a way for the residents to demonstrate their willingness to fight in defense of their territory. (Rosell, 1997) Beavers respond to the scent mounds of a non-familiar beaver, marked with castoreum, by sniffing, straddling, pawing, and over marking, also called counter marking (Lixing Sun 1988, 1997). Castoreum is a mixture of secondary metabolites from urine and it is secreted from the castor sacs. The ideal substance for scent marking a territory is thought to be one that has minimal energetic costs to the signaler. Castoreum is thought, for this reason, to be an ideal substance. (Rosell, 2001). Although the anal gland secretion (AGS) is also used to scent mark on occasion, the hypothesis is that the AGS is used more for kin recognition and communication than territorial defense. Kin Recognition and AGS Scientists hypothesize that scent marking and olfactory communication is primarily utilized because their visual and acoustic communication is poorly developed. The only acoustic communication the beaver uses is the tail slap. Also, since beavers are primarily nocturnal, they are not able to rely on visual communication. (Rosell, 1998) Why a Classical Territory? Beavers live in a classical territory because of predation pressures and because of the high amount of investment that goes into establishing a territory. The beaver dam and lodge (substituted for a bank den in some situations) requires the work of the entire colony. The dam creates an aquatic environment that allows the beaver to avoid its terrestrial predators. Lodge openings that are located underwater also deter predators from invading the beaver’s home (Jackson 1997). Since beavers invest so much time into modifying their habitat, they are not able to continually relocate. For this reason, they must also defend their territory from non-family beavers looking to establish their own colony.

Continue to the next page on The Mating System and Social Relationships Link to Literature Cited Return to Beaver Home Page Return to Animal Behavior Home Page Return to Davidson College Biology Department Home Page This page was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2003.