As alarm calls indicate the presence of predators, the correct interpretation of alarm calls, including those of other species, is essential for predator avoidance. Conversely, communication calls of other species might indicate the perceived absence of a predator and hence allow a reduction in vigilance. This ‘‘eavesdropping’’ was demonstrated in birds and mammals, including lemur species. Interspecific communication between taxonomic groups has so far been reported in some reptiles and mammals, including three primate species. So far, neither semantic nor interspecific communication has been tested in a solitary and nocturnal lemur species.
The aim of our study was to investigate if the nocturnal and solitary Sahamalaza sportive lemur, Lepilemur sahamalazensis, is able to access semantic information of sympatric species.
Sahamalaza sportive who?
As a solitary species, the Sahamalaza sportive lemur doesn’t have the benefit of relying on group members to warn of predators. Despite being nocturnal, this species rests very exposed during the day and is essentially vigilant all the time to watch for potential attackers. The fossa, the Madagascan harrier hawk, the tree boa snake, and humans hunting for bushmeat are the main threats. The sportive lemurs’ natural habitat on the Sahamalaza peninsula has suffered greatly from slash and burn agricultural practices and deforestation for plantations, leaving only 200 hectares of its home forest left. As a result, the Sahamalaza sportive lemur is among the most critically endangered animals and was placed on the IUCN’s “red list” in 2012. In the field, we have not seen more than 29 individuals in a single season.
What did we do?
My team and I spent 12 months out at the remote Ankarafa field station in northwestern Madagascar, set up by co-author Christoph Schwitzer and run by the Lemur Conservation Association. For this study, we presented alarm calls of the crested coua, the Madagascar magpie-robin and aerial, terrestrial and agitation alarm calls of the blue-eyed black lemur to 19 individual Sahamalaza sportive lemurs resting in tree holes during the day. Songs of both bird species’ and contact calls of the blue-eyed black lemur were used as a control.
What have we found?
After alarm calls of crested coua, Madagascar magpie-robin and aerial alarm of the blue-eyed black lemur, the sportive lemurs scanned up and their vigilance increased significantly. After the presentation of terrestrial alarm and agitation calls of the blue-eyed black lemur, the animals did not show significant changes in scanning direction or in the duration of vigilance. Sportive lemurs vigilance decreased after playbacks of songs of the bird species and contact calls of blue-eyed black lemurs.
What are the conclusions of our study?
Our results suggest that the Sahamalaza sportive lemur is not only capable of correctly classifying alarm calls of different surrounding species, but the ‘all clear’ calls, too. As the presented alarm calls differ structurally, we were able to exclude the possibility that the lemurs simply react to a certain call structure and conclude that the reaction towards the different calls types is based on a learning process.
Evolutionary, it makes perfect sense that a nocturnal, solitary creature like the sportive lemur has developed a way of staying safe during the day – in the case of the Sahamalaza sportive lemur being aware of its environment and the other animals it shares its habitat with. As there are 26 different sportive lemur species living in Madagascar, which are similar in appearance and behavior, this ‘‘eavesdropping’’ is likely not unique to the Sahamalaza sportive lemur.
Do you want to know more? Find the publication here.
If you want to know more about the work of Melanie Seiler, find her on research gate, or contact her at firstname.lastname@example.org.
Citation: Seiler M, Schwitzer C, Gamba M, Holderied MW (2013) Interspecific Semantic Alarm Call Recognition in the Solitary Sahamalaza Sportive Lemur, Lepilemur sahamalazensis. PLoS ONE 8(6): e67397. doi:10.1371/journal.pone.0067397