A rare case of cannibalism involving two adult mouse lemurs in Kirindy, Western Madagascar, is reported in the May 23 issue of The American Journal of Primatology.

As sometimes happens in scientific research, pure chance sometimes plays a key role in new discoveries. Anni Hämäläinen, a PhD student at the University of Göttingen and the author of this report, was following a lemur as part of her research on sex differences in aging when she ran into an oddly behaving lemur. As she shared with The Munich Times, "When I saw the event, I was searching for a radio-collared individual. When I spotted the reflection of the radio collar and the animals' eyes from far away, I was surprised by the unusual way they were moving and therefore assumed that something interesting was happening." 

The first things that came to her mind was a mating, or perhaps two animals grooming each other or feeding on something. "As I approached, however, I was quite shocked to find that the animal I had been searching for was, in fact, not only dead but completely gutted and another mouse lemur was feeding on her spine in a frenzy." The female in question, named 374B, had been out of sight for little over one hour when Anni Hämäläinen found it, dead and being eaten by a male of the same species. The body and head of the dead female had been torn open and was missing all of its internal organs and the brain. The cannibalistic male was found feeding on the spinal cord, and continued feeding on the body for 20 minutes after sighting.

Cannibal lemurs
Cannibalism has been observed in a wide variety of organisms, from bacteria to humans. And reasons behind this behaviour differ from species to species, including sexual cannibalism as seen in the praying mantis, or infanticide, as seen in many vertebrates, or even include cultural reasons, as seen in humans. Difficult environmental conditions, leading to scarce resources and as a consequence starvation, may also trigger such behaviour. In primates, several species are known to feed on members of their own species, but in all reported cases it involves an adult feeding on a sub-adult, such as an infant. The current thought is that adults do not feed on other adults even after killing the victim themselves.

This single report is unique in that it involved two wild adults, although it does not imply a case of predatory behavior, as the actual cause of death of the female is unknown. Most likely, this particular event was influenced by harsh nutritional circumstances, as it occurred during a period of low food availability. As the author explains, "The main significance of this case is that cannibalism of adult victims has not previously been seen in any wild non-human primates and consequently this expands on our knowledge of the cannibalism phenomenon as well as the flexibility of diet and behavior of mouse lemurs...I presume that when the benefits outweigh the costs, it can be adaptive for an animal to make use of such an unusual food item. "

Assuming there is low risk of disease transmission, feeding on a fellow lemur can be a very nutritionally profitable behavior, and can mark the difference in whether the individual survives until the next feeding opportunity or not. So when things get tough and the opportunity arises, lemurs and perhaps other vertebrates may briefly become cannibals.