Effect of social organisation on interspecific differences in overmarking behaviour of foals in African equids

Why wait to mark? Possible reasons behind latency from olfactory exploration to overmarking in four African equid species

Whereas most studies on overmarking in mammals analysed the rate of overmarking, that those investigate time between exploration of an olfactory stimulus and the response to it remain less common, with inconsistent results. We examined the latency in time between elimination by the sender and sniffing by the receiver, and from sniffing and overmarking, in four captive African equid species to explore differences among species, and among age and sex classes. We investigated these latency time periods in light of three potential hypotheses explaining overmarking behaviour in equids: social bonds, group cohesion, and intrasexual competition. Analysing 1684 events of sniffing and 719 of overmarking among 130 individuals, we found that (i) the time from elimination to overmarking was shorter among female friends and in parent-offspring dyads, proving support to the social bond hypothesis; (ii) intraspecific differences in time periods do not reflect the social organisation of species, thus not supporting the group cohesion hypothesis; (iii) males were more attracted to elimination of conspecifics than females, and female's eliminations were inspected longer, in line with the sexual competition hypothesis and/or reproductive behaviour. In addition, we found that the younger foals came to sniff eliminations faster than older ones, and in larger groups foals devoted longer time to sniffing the elimination before overmarking. We concluded that examination of the elimination could be driven by motivations other than the decision to overmark. Whereas overmarking serves to express bonds to a familiar individual, the latency of overmarking reflects more reproductive interests.

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.