The Cao Vit gibbon (Nomascus nasutus) was rediscovered in 2002 in Vietnam and then in 2006 in China. This is the only known population with about 110 individuals located along the China-Vietnam border. Little is known about it other than its population size and distribution. We describe the social structure and group dynamics of the Cao Vit gibbons in China based on 2 years of monitoring from 2007 to 2009. Four established study groups at this site consisted of 1 adult male, 2 adult females and 2–6 offspring. Two juveniles in 2 groups disappeared during the research. Four infants were born in 3 groups from November 2008 to February 2009. In 2 of the groups, both adult females had dependent infants. These observations suggest that Cao Vit gibbons live in polygynous groups, contrary to the usual monogamous group with only 1 adult female, but nevertheless similar to the social organization of both N. concolor and N. hainanus. We observed a coordinated dispersal of 1 adult male and 2 large juveniles, and the male formed a pair with a newly arrived female. Our observations support a growing awareness of variability in gibbon social organization.
Although primate females are predicted to develop counterstrategies against male infanticide, it has remained unclear whether counterstrategies are effective. Detailed long-term observations in Rhinopithecus roxellana reveal that females are able to mount versatile counterstrategies, including extra-unit mating, female joint defense and transfer with the infants, which lead to only 4 of 31 infants succumbing to infanticide and no difference in mortality of infants present during male replacements compare to other periods. Female joint defenses crucially delay infanticide and provide an opportunity for mothers' transfer to another social unit. In response to mothers' transfer, some males cease attacking infants, which is likely beneficial to males as during longer tenure they can sire future offspring of the mothers who remain. Our findings show how dynamic interactions between males and females can be and how the conditions in multilevel societies can shift the balance of intersexual conflict from males to females.
Human activity is increasingly and persistently disturbing nature and wild animals. Affected wildlife adopts multiple strategies to deal with different human influences. To explore the effect of human activity on habitat utilization of the Himalayan marmot (Marmota himalayana), habitat utilization patterns of three neighboring marmot populations in habitats affected differently by human activities were recorded and compared. We found that: (1) Distance between reproductive burrows becomes shorter under the influence of human activity, and further, the more disturbance a population suffers, the more burrows were dug as temporary shelter to reduce the distance to those shelters when threatened. More burrows that are closer in the disturbed habitats improve ability to escape from threats. (2) Burrow site selection is determined by the availability of mounds in the habitat. Breeding pairs selectively build burrows on mounds to reproduce, potentially to improve surveillance and the drainage of their burrows. Human activities generally drive breeding pairs away from the road to build their reproductive burrows, likely to reduce disturbance from vehicles. However, even heavy human activity exerts no pressure on the distance of reproductive burrows from the road or the mound volume of the high disturbance population, potentially because mounds are the best burrowing site in the habitat. Marmots deal with nonlethal human disturbance by digging more burrows in the habitat to flee more effectively and building reproductive burrows on mounds to gain better vigilance and drainage efficiency.
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