Estimating the population size of the Sanje mangabey (Cercocebus sanjei) using acoustic distance sampling.

The Sanje mangabey (Cercocebus sanjei) is endemic to the Udzungwa Mountains, Tanzania, and is classified as Endangered due to its putatively declining population size, habitat degradation and fragmentation. Previous population size estimates have ranged from 1,350 to 3,500 individuals, with the last direct survey being conducted 15 years before the present study. Previous estimates are now thought to have underestimated the population due to a limited knowledge of group and habitat size, nonsystematic approaches and the use of visual methods that are not suitable for surveying the Sanje mangabey with its semi-terrestrial and elusive behaviors. We used an acoustic survey method with observers recording the distinctive "whoop-gobble" vocalization produced by mangabeys and point transect distance sampling to model a detection function and estimate abundance. Twenty-eight surveys were conducted throughout the two forests where Sanje mangabeys are found: Mwanihana forest in the Udzungwa Mountains National Park (n = 13), and the Uzungwa Scarp Nature Reserve (n = 15). Group density was found to be significantly lower in the relatively unprotected Uzungwa Scarp forest (0.15 groups/km2 ; 95% CI: 0.08-0.27) compared to the well-protected Mwanihana forest (0.29 groups/km2 ; 95% CI: 0.19-0.43; p = .03). We estimate that there are 1,712 (95% CI: 1,141-2,567) individuals in Mwanihana and 1,455 (95% CI: 783-2,702) in the Uzungwa Scarp, resulting in a total population size of 3,167 (95% CI: 2,181-4,596) individuals. The difference in group density between sites is likely a result of the differing protection status and levels of enforcement between the forests, suggesting that protection of the Uzungwa Scarp should be increased to encourage recovery of the population, and reduce the threat of degradation and hunting. Our results contribute to the reassessment of the species' IUCN Red List status and informing management and conservation action planning.

Ecology of reproduction in Sanje mangabeys (Cercocebus sanjei): dietary strategies and energetic condition during a high fruit period.

The ability to increase energy storage when food is abundant for later use during late gestation and early lactation is often considered the primary benefit of the capital breeding strategy (clustering conceptions during high food periods, HFP) that promotes reproductive success among females living in unpredictable environments. Capital breeding, however, may also enable preconceptive females to increase hormone production for ovulation, which has been linked to energetic condition in capital breeders, and/or allow females entering the subsequent HFP to increase their energetic condition in order to continue nursing unweaned infants. Here, we investigate whether capital breeding provides these additional benefits in 16 female Sanje mangabeys (Cercocebus sanjei) and determine the dietary strategies used to increase energetic condition (measured by urinary C-peptide: UCP) during the HFP. Fecal estradiol (fE2 ) and UCP were negatively correlated with number of cycles before conception (r = -0.591, r = -0.646, P < 0.01) and were highest in conceptive cycles. Both peri-conceptive (preconception and early gestation) and non-peri-conceptive (lactation) females increased energetic condition over the HFP (r = 0.612, r = 0.583, P < 0.001) by increasing dietary fat (r = 0.619, r = 0.703, P < 0.001) and, for non-peri-conceptive females, protein (r = 0.437, P < 0.001). Feeding intake rate (FIR) and time spent foraging and feeding did not change over the HFP; however, non-peri-conceptive females exhibited a faster FIR compared to peri-conceptive females (t = -2.324, P < 0.05), consuming almost twice as much food per unit time. The results of this study confirm that Sanje mangabeys benefit in multiple phases of the reproductive cycle by using capital breeding, which may explain how this strategy promotes female reproductive success.