I was watching a nature documentary last night. It seems that several species of monkey (e.g. Diana monkeys, Spot Nose Guenons, Campbell's monkeys, and others) in the Tai forest of West Africa move together through the canopy in what is called a 'monkey alliance'.
Like many monkeys, each species within the Alliance has its own set of predator-specific alarm calls, i.e. 'Holy sh%t, big eagle coming in', etc. The interesting twist of these Alliances is that the different alarms calls are understood by the other species too. So, if a Diana spots a leopard and sounds the alarm, not only the other Dianas go on alert but also monkeys from the other species.
Pretty inefficient. I'm a young Guenon and I'm expected to not only learn my own species' calls but those of every other species I hang around with? And what happens when a new Alliance member joins up? Adult education classes?
Barring some sort of cross-species standard for alarm calls (you'd never get each species to give up their own calls, you know how primates are), you would have thought the different monkeys could have at least got together in a non-partisan location and thrashed out some basic guidelines for reconciling the various call systems. Maybe something as simple as high-pitched calls for threats from above, low pitched calls for threats from the ground.
Monkey alliances are viable because each species within generally obtains food in different ways (e.g. at different levels within the forest canopy, flowers versus fruit, etc) so they don't directly compete with each other. Hmmm.