The chimps are up to something.聽A massive study has found that the majority of chimp populations are sometimes active at night but cannot tell us why.
Chimps鈥� nocturnal behaviours have barely been studied, says of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. 鈥淩esearchers in the field follow them from the time they get out of their nest in the morning to the time they nest around twilight hours,鈥� she says.
鈥淲hat happens between the time they nest in the evening and the following morning has largely been a mystery.鈥� However, in 2014 it emerged that .
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McCarthy is part of a research team that compiled data from 22 chimp research sites in Africa. They used ground-based camera traps to see what the chimps did at night.
The camera traps spotted chimps out and about at night at 18 of the 22 sites. It happened at all hours of the night but was most common at twilight. In most cases, the chimps were simply snapped moving past the camera.
鈥淲e don鈥檛 know what they were doing,鈥� says McCarthy. 鈥淚t could be they were travelling to feeding sites and feeding in the night, or it could be they were changing from one nest location to another.鈥� It may be significant that lone males were the most frequently observed. 鈥淚t could be males either doing patrolling behaviours, or seeking out mating opportunities.鈥�
In total about 2 per cent of the chimps鈥� recorded activity took place at night, but McCarthy says it could be much more. For one thing, the camera traps will have missed any activity up in the trees.
A study published in February found that chimps in Fongoli, Senegal were 鈥� perhaps feeding at night rather than in the heat of the day. A third study, , used acoustic sensors to show that chimps also call at all hours of the night.
McCarthy and her colleagues were surprised to find that chimps were more likely to be active at night in areas with a low human presence. Many animals are becoming more nocturnal to avoid encounters with humans, but chimps buck that trend. It may be because human hunters are sometimes active in the early evening and early morning, so chimps living near humans stay quiet at those times.
