Sanje mangabey Project
I have worked in Tanzania since 2007. In collaboration with Dr Grainne McCabe (Bristol Zoological Society, England) we established the Sanje Mangabey Project, a research initiative aimed at studying and protecting the Endangered Sanje mangabey (Cercocebus sanjei), a monkey species endemic to the Udzungwa Mountains of Tanzania.
The Udzungwa Mountains are also known as the Galapagos of Africa for the high levels of endemism, species that are found only here and nowhere else in the world. Among these species, the Sanje mangabey is one of the most emblematic and most threatend. Their total population size is estimated to be of less than 3500 individuals. Moreover, their population is divided into two isolated sub-populations: one in the Udzungwa Mountains National Park, relatively well protected; and another one in the Udzwungwa Scarp Nature Reserve, where logging, poaching and habitat transformation seriously threaten their survival.
With current funding from the Bristol Zoological Society we maintain a long-term study of a habituated group of Sanje mangabeys. Our team of extremely dedicated team of local field assistants follow them for two weeks every month collecting data on their life history (i.e., births, deaths, weaning), sexual behavior, diet and habitat use. We will use this information to model their population viability and to predictive their survival under different conservation scenarios. Additionally, we are increasing the passive protection of the Udzwungwa Scarp Nature Reserve via monthly censuses across the Reserve. Finally, with support from NERC Industrial Case PhD Studentship, we are also finalising a population-wide survey to obtain a more accurate estimate of their population size, as their last census was conducted in 2001.
The Udzungwa Mountains are also known as the Galapagos of Africa for the high levels of endemism, species that are found only here and nowhere else in the world. Among these species, the Sanje mangabey is one of the most emblematic and most threatend. Their total population size is estimated to be of less than 3500 individuals. Moreover, their population is divided into two isolated sub-populations: one in the Udzungwa Mountains National Park, relatively well protected; and another one in the Udzwungwa Scarp Nature Reserve, where logging, poaching and habitat transformation seriously threaten their survival.
With current funding from the Bristol Zoological Society we maintain a long-term study of a habituated group of Sanje mangabeys. Our team of extremely dedicated team of local field assistants follow them for two weeks every month collecting data on their life history (i.e., births, deaths, weaning), sexual behavior, diet and habitat use. We will use this information to model their population viability and to predictive their survival under different conservation scenarios. Additionally, we are increasing the passive protection of the Udzwungwa Scarp Nature Reserve via monthly censuses across the Reserve. Finally, with support from NERC Industrial Case PhD Studentship, we are also finalising a population-wide survey to obtain a more accurate estimate of their population size, as their last census was conducted in 2001.
Behavioural ecology and reproduction of the Sanje mangabey
Sanje mangabeys live in multi-male, multi-female groups with a highly female-biased sex ratio. That means that there are many more females than males. As such, when females are fertile and look for a male to mate with, males must compete for access to females. Not only that, around the time of ovulation female Sanje mangabeys’ produce what is known as a ‘sexual swelling’, and enlargement of their perineal area that is thought to be a “tool” to further confuse males about their fertility. Or does it…? What do males really know about female fertility…?
I have found that Sanje’s sexual swellings provide accurate information about the timing of ovulation, as ovulation occurs when the swelling is at maximum tumescence, and particularly when the swelling skin changes and becomes a brighter color (AKA ‘the shiny phase’). Moreover, the sexual swellings of females of different fertility (e.g., females undergoing conceptive cycles vs. females with post-conceptive swellings) and age (e.g., adults vs. adolescents) differ in the duration of the maximum tumescence and/or shiny phase, and that their levels of faecal estradiol – a hormone that is directly related to a female’s fertility - increases as the females undergoes ovarian cycles. All of this suggests that the sexual swellings of Sanje mangabeys can convey information about their fertility that males may use to select mates. Males are also able to estimate female quality, as they exhibit greater interest on females undergoing what would become conceptive cycles. In addition, my research found that male rank determines access to fertile females, but that males’ ability to monopolize females decreased as the number of available females increased, as well as during periods of male rank instability caused by a group take over by an immigrant male.
What does it all mean? Well, it seems that male Sanje mangabeys have relatively accurate information of female fertility, despite females attempt to confuse fertility among males, but that external factors, such as male migration, can significantly affect male’s ability to actually act upon this knowledge and target the most fertiles females.
I have found that Sanje’s sexual swellings provide accurate information about the timing of ovulation, as ovulation occurs when the swelling is at maximum tumescence, and particularly when the swelling skin changes and becomes a brighter color (AKA ‘the shiny phase’). Moreover, the sexual swellings of females of different fertility (e.g., females undergoing conceptive cycles vs. females with post-conceptive swellings) and age (e.g., adults vs. adolescents) differ in the duration of the maximum tumescence and/or shiny phase, and that their levels of faecal estradiol – a hormone that is directly related to a female’s fertility - increases as the females undergoes ovarian cycles. All of this suggests that the sexual swellings of Sanje mangabeys can convey information about their fertility that males may use to select mates. Males are also able to estimate female quality, as they exhibit greater interest on females undergoing what would become conceptive cycles. In addition, my research found that male rank determines access to fertile females, but that males’ ability to monopolize females decreased as the number of available females increased, as well as during periods of male rank instability caused by a group take over by an immigrant male.
What does it all mean? Well, it seems that male Sanje mangabeys have relatively accurate information of female fertility, despite females attempt to confuse fertility among males, but that external factors, such as male migration, can significantly affect male’s ability to actually act upon this knowledge and target the most fertiles females.