Abstract
Territorial animals carry out extra-territorial movements (forays) to obtain pre-dispersal information or to increase reproductive success via extra-pair copulation. However, little is known about other purposes and spatial movement patterns of forays. In this study, we GPS-tagged 54 Eurasian beavers (Castor fiber), a year-round territorial, monogamous mammal, during the non-mating season. We investigated forays in territory-holding breeders (dominants) and non-breeding (subordinate) family members. Twenty of 46 dominant individuals (44%), and 6 of 10 subordinates (60%) conducted forays. Generally, beavers spent between 0 and 11% of their active time on forays, travelled faster and spend more time in water when on forays compared to intra-territorial movements, suggesting that forays are energetically costly. Further, beavers in smaller territories conducted more forays. Possibly, smaller territories might not have sufficient resources and thus dominant individuals might conduct forays to assess possibilities for territory expansion, and potentially for foraging. Generally, besides territory advertisement (e.g. via scent-marking), forays might serve as an additional mechanism for territory owners to assess neighbours. Subordinates spent more time on forays, moved greater distances and intruded into more territories than dominant individuals did, suggesting that they prospected to gain information on the population density and available mates before dispersal.
Highlights
Animals are territorial when the benefits of holding a territory exceed the total costs of territory defence[1]
Extra-pair copulations have been recorded in a North American beaver population[30], suggesting that forays occur during the mating season, whereas there is little evidence for extra-pair copulations in Eurasian beavers[31,32]
We GPS tagged a total of 54 individuals: 46 dominant individuals consisting of females (7 were tagged multiple times) and males (6 were tagged multiple times), and 10 subordinate (4 females and 6 males) beavers
Summary
Animals are territorial when the benefits of holding a territory (defined as the exclusive access to limited resources, such a food, mating partners and shelter) exceed the total costs of territory defence[1]. Three types of forays are distinguished: (1) Adults seeking extra-pair copulations[12,13,14] This type of foray relies on information about neighbours[15] and habitat structure[8] and is usually limited to the reproductive season[16]; (2) Forays by subordinate individuals (non-breeders) to gain experience and information about dispersal opportunities[16,17,18,19]; and (3) Forays to increase foraging success. Apart from gaining foraging opportunities, little is known about the role of forays of year-round territory holders outside of the mating season, and especially about the movement patterns during forays in general[3]. We hypothesized that movement patterns would differ between intra-territorial movements and forays, and predicted that individuals would travel at a greater speed and spend less time on land during forays compared to intra-territorial movements
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