Hamburg  - Forget online chat rooms, tiny flying lemurs in the rain forests of Madagascar find just the right partners the old- fashioned way, with a moonlight serenade which they croon with a sexy vocal accent, according to German researchers.

And not only do the prospective mates recognize these love songs, they also recognize subtle variations in "dialect" which indicate sub-species among these tiny tree-top creatures.

Males of these nocturnal species use these serenade calls to let females know that they are looking for love.

The researchers recorded advertising calls from the three species and then played them back to grey mouse lemurs, noting what response, if any, they made.

"Grey mouse lemurs reacted more to calls from other grey mouse lemurs than to those of either other species," says Dr. Pia Braune and colleagues from the Institute of Zoology, University of Veterinary Medicine, Hanover University.

Furthermore, the grey mouse lemurs seemed to ignore the calls of golden brown mouse lemurs, who live in the same area and habitat as them, but show some interest in the calls of Goodman's mouse lemur, which they would never normally meet.

"The importance of vocalisation in attracting mates is well known for frogs and birds," explain the authors in the journal BMC Biology, "but this is the first evidence for species-specific call divergence in the communication of cryptic primate species with overlapping ranges."

Until recently, grey, golden brown and Goodman's mouse lemurs were all thought to be the same species. But genetic testing revealed that they are, in fact, three distinct, species so similar that they cannot be distinguished by their appearance - so called cryptic species.

"A fundamental problem for cryptic species that live in the same area and habitat is the coordination of reproduction and discrimination between potential mates of the same species and remarkably similar individuals of other species," says Dr Braune.

"The lemurs' moonlight serenades help to ensure that individuals of one species don't waste time trying to mate with those of another, which would produce either no offspring or infertile hybrids," Braune adds.

Indeed, the possibility of grey and golden-brown mouse lemurs encountering each other might explain the difference in calls and responses, according to Braune.

She says, "Our data support the evolutionary hypothesis that species cohesiveness has led to divergence in signalling and recognition to avoid costly hybridisation." (dpa)