Size is not everything: differing activity and foraging patterns between the sexes in a monomorphic mammal

Abstract

Animals balance foraging with other activities, and activity patterns may differ between sexes due to differing physical requirements and reproductive investments. Sex-specific behavioural differences are common in sexually dimorphic mammals, but have received limited research attention in monomorphic mammals where the sexes are similar in body size. Eurasian beavers (Castor fiber) are obligate monogamous and monomorphic mammals and a good model species to study sex-specific differences. As females increase energy expenditure during reproduction, we hypothesized differing seasonal activity budgets, circadian activity rhythms and foraging patterns between male and reproducing female beavers. To test this hypothesis, we equipped adult beavers with VHF transmitters (N=41; 16 female, 25 male) and observed them throughout their active period at night from spring to late summer. Occurrence of their main activities (foraging, travelling and being in lodge) and use of food items (trees/shrubs, aquatic vegetation and herbs/grasses) were modelled to investigate sex-specific seasonal activity budgets and circadian activity rhythms. The sexes did not differ in time spent foraging across the season or night, but during spring, females resided more in the lodge and travelled less. Males and females both foraged on aquatic vegetation during spring, but females used this food source also during late summer, whereas males mostly foraged on trees/shrubs throughout the year. We conclude that seasonal activity budgets and foraging differ subtly between the sexes, which may relate to different energy budgets associated with reproduction and nutritional requirements. Such subtle seasonal behavioural adaptions may be vital for survival and reproduction of monomorphic species. Significance statement Activity budgets and foraging patterns of animals are key to their survival and may differ between males and females with different body sizes and physical requirements. In monomorphic species, where males and females have similar body sizes, fewer differences are expected, but may still be pronounced during certain times of the year. We modelled sex-specific seasonal activity budgets and circadian activity rhythms and use of food items in a monomorphic mammal, the Eurasian beaver. By treating season and time of day as a continuous variable rather than modelling differences within distinct predefined periods, we identified subtle sex-specific seasonal trends in activity budgets and use of food items.

Aquatic habitat use in a semi-aquatic mammal: the Eurasian beaver

“…Other studies on semi-aquatic mammals show how males and females in two species of shrew (Neomys fodiens and Sorex coronatus) use separate foraging habitats during the breeding season [165]. Males and females in our population have been shown to differ seasonally in aquatic foraging with peaks in the spring and late summer for females, whereas males only foraged on aquatic vegetation in the spring [166]. We found that selection for the focal plant species were statistically stronger among subordinate individuals, which may be linked to their higher energetic requirements resulting from their activities related to attempts to become dominant in a territory [57] (e.g.…”

Influence of Moon Luminosity, Seasonality, Sex and Weather Conditions on the Activity Levels of the Nocturnal Javan Slow Loris

“…The low activity levels can also be due to the fact that female lorises park their infants and stay in proximity to their infants during the first months of life to return to visit the infant during foraging periods [56]. We did not include reproductive periods in the model as births in Javan slow loris are aseasonal, but reproductive state may have played an important role in shaping activity levels since females were either on gestation or lactation periods during the data collection [29,57]. Behavioral observations indicate that females tend to have a higher consumption of crude proteins, fruits, gum, and flowers during gestation and lactation than males [41], and they tend to have higher feeding time than males [58].…”

“…Activity patterns can also differ between sexes, with females that can have either lower or higher energy intakes/costs than males during lactations and gestations [28]. The choice of either maximizing energy intake or minimizing energy expenditure depends on species and environmental conditions [29,30]. There are, however, cases when the activity patterns of females do not differ from those of males, even during periods of high energy needs (e.g., [31]).…”

Marginal additive models for population‐averaged inference in longitudinal and cluster‐correlated data

“…The original analysis fit a GAMM with a logit link to flexibly model seasonal trends in foraging behavior while accounting for repeated measurements (Lodberg-Holm et al, 2021). By including beaver-level intercepts, this approach yielded inference for "beaver-specific" associations.…”