Does social facilitation affect suckling behaviour in zebras?

Many recent studies show that synchronisation of various behaviours are advantageous for group-living mammals. However, studies on synchronisation of suckling behaviour inmonotocous species are nearly absent. We observed 49 individual foals of three zebra species in Dvůr Králové Zoo, and recorded a total of 5 890 suckling bouts, almost one fifth (1 036) of which were synchronised (defined as at least two bouts overlapping at the same time). We found that synchronised suckling bouts lasted longer and were less likely to be terminated by the mother than non-synchronised ones. This is in line with social facilitation theory. In addition the occurrence of synchronised suckling bout differed interspecifically. In plains (Equus quagga) and mountain zebra (E. zebra) the probability of synchronised bouts increased with increasing numbers of foals, whereas the opposite result was found in Grevy's zebra (E. grevyi). We suggest that the interspecific differences may reflect differences in social organisation of respective species as suckling synchronisation rate was higher in species that form nurseries in the wild.