• Scent-marking investment and motor patterns are affected by the age and sex of wild brown bears

      Clapham, Melanie; Nevin, Owen T.; Rosell, Frank; Ramsey, Andrew; University of Derby (Elsevier, 2014-07-01)
      Members of the Carnivora employ a wide range of postures and patterns to mark their scent onto objects and thereby communicate with conspecifics. Despite much anecdotal evidence on the marking behaviour of ursids, empirical evidence of scent-marking motor patterns displayed by wild populations is lacking. Analysing the time that different age and sex classes spend at scent-marking trees and the behaviours involved at different times of year could provide further insight into the function of marking. We used camera traps stationed at scent-marking trees to investigate scent-marking behaviour by wild brown bears, Ursus arctos. Through image-based data, we found evidence to support the hypothesis that time investment and scent-marking motor patterns are dictated by the age and sex of the bear. Adult males spent more time scent marking and displayed a more complex behavioural sequence of marking than adult females and juveniles. Adult male behaviour at marking trees was consistent throughout the year, indicating a continued benefit of chemical signalling outside of the breeding season. Juvenile bear behaviour at marking trees changed with age. Young dependent cubs were more likely to imitate their mother's behaviour, whereas older dependent cubs were more likely to engage in marking behaviour independently. The marking motor patterns of independent subadults were more simplistic than those of younger dependent cubs, suggesting a change in behaviour with independence. We suggest that these findings further support the hypothesis that scent-marking behaviour by brown bears functions in intrasexual competition between adult males. Cub behaviour at marking trees suggests an influence of social learning.
    • Till death (or an intruder) do us part: intrasexual-competition in a monogamous Primate

      Fernández-Duque, Eduardo; Huck, Maren; University of Pennsylvania, Department of Anthropology; Centro de Ecologia Aplicada del Litoral, CONICET (2013)
      Polygynous animals are often highly dimorphic, and show large sex-differences in the degree of intra-sexual competition and aggression, which is associated with biased operational sex ratios (OSR). For socially monogamous, sexually monomorphic species, this relationship is less clear. Among mammals, pair-living has sometimes been assumed to imply equal OSR and low frequency, low intensity intra-sexual competition; even when high rates of intra-sexual competition and selection, in both sexes, have been theoretically predicted and described for various taxa. Owl monkeys are one of a few socially monogamous primates. Using long-term demographic and morphological data from 18 groups, we show that male and female owl monkeys experience intense intra-sexual competition and aggression from solitary floaters. Pair-mates are regularly replaced by intruding floaters (27 female and 23 male replacements in 149 group-years), with negative effects on the reproductive success of both partners. Individuals with only one partner during their life produced 25% more offspring per decade of tenure than those with two or more partners. The termination of the pair-bond is initiated by the floater, and sometimes has fatal consequences for the expelled adult. The existence of floaters and the sporadic, but intense aggression between them and residents suggest that it can be misleading to assume an equal OSR in socially monogamous species based solely on group composition. Instead, we suggest that sexual selection models must assume not equal, but flexible, context-specific, OSR in monogamous species.