The birth hour of mammals: insights from intra-specific variation in wild blue monkeys

While most mammals show birth hour peaks at times of the 24-hour cycle when they are less active, there are exceptions to this general pattern. Such exceptions have been little explored, but may clarify evolutionary reasons for the diel timing of births. We investigated intraspecific variation in birth hour in wild blue monkeys Cercopithecus mitis stuhlmanni, a diurnal primate, to identify factors that differentiated daytime vs. nighttime births. Behavioral and life history data from 14 groups over 14 years revealed that 4% of 484 births occurred during the day. Probability of daytime birth varied with mother’s age, peaking at 15.7 years. Births whose annual timing deviated most from the population’s peak birth months were five times more likely to occur during daytime than those that deviated less. There was no evidence that mother’s rank or infant sex influenced birth hour, and mixed evidence that daytime births were more probable in larger groups. Survivorship did not differ significantly for infants born during the day vs. night. Prime-aged mothers may be able to handle the consequences of an unusual birth hour more successfully than mothers with less experience or those weakened by age. Daytime birth may be more advantageous in the off-season because nights are colder at that time of year. These findings are consistent with hypotheses relating birth hour to the risk of losing social protection in group-living animals, but are not consistent with those emphasizing risk of conspecific harassment. Patterns of within-species variation can help in evaluating evolutionary hypotheses for non-random birth hour.

Population Size, Activity Patterns, Diet, and Ranging Ecology of Boutourlini’s Blue Monkey (Cercopithecus mitis boutourlinii) in Apini and Dokuma Forests, Awi Zone, Ethiopia

Background: By studying population size, activity patterns, diet, and ranging ecology of Boutourolini’s blue monkey (Cercopithecus mitis boutourlinii) we can get sufficient information to conserve the subspecies in the area. Boutourlini’s blue monkey is endemic subspecies found in the western and northwestern parts of Ethiopia. The study was conducted in Apini and Dokuma forests, northwestern Ethiopia, from October 2018 to June 2019. The block count method was used to estimate its total population size and scan sampling method was used to collect data for activity patterns, and diet. The ranging ecology of the study subspecies was determined for each group based on the point to point movements of the group between consecutive GPS locations recorded. Results: On average a total of 71 and 111 individuals of Boutourolini’s blue monkey were counted in Apini and Dokuma forests, respectively. Boutourolini’s blue monkey spent 47.5% and 48.6% of time feeding, 20.2% and 18.6% moving, and 14.1% and 13.5% resting by the Apini and Dokuma groups, respectively. The Apini group frequently fed on young leaves (52.8%), fruits (30.2%), and mature leaves (6.6%), while the Dokuma group fed on young leaves (39.8%), fruit 942.3%), and mature leaves (8.3%). Ranging ecology of Boutourolini’s blue monkey was 44.4 ha and 78.3 ha for the Apini group, and 51 ha and 56.9 ha for the Dokuma group during the wet and dry seasons, respectively. Conclusions: The total population size of blue monkeys in the Apini and Dikuma forests counted were different. Activity budgets vary during the wet and dry seasons. During the entire study period blue monkeys consumed different food items from the two forests. The home range size of blue monkeys during the two seasons was different in both groups and they traveled long distance during the dry season. As the habitats of Boutourolini’s blue monkey in the present study area is degraded due to various anthropogenic activities, there is a need to design strategies to minimize conservation problems of the subspecies in the area.