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September 26, 2018

Zebras, too, have social rules

Gravy Zebras stops to let common zebras get together
Gravy Zebras stops to let common zebras get together

Something good is happening within Samburu National Reserve. The once lost gravy’s zebras are now found. The beautiful beasts have come back from wherever they had gone to, and they have decorated the park back to its original appeal. It is now common to see a group of more than 100 together, something that was a rarity during the last several years. Two years ago I was in this reserve for three nights with friends and we saw only three individuals. Most of us were worried especially when we saw some of the zebras had radio collars, meaning they were being closely monitored by researchers. Without a better explanation, we had sadly assumed the worst. The gravy’s zebra was about to go extinct. Now we are relaxed.

As I watched the gravy’s zebras, something struck my attention. It was a very hot day in this semi desertic area of Samburu. There were also the common zebras grazing together with the gravy’s. When it was time for them to seek water, it was the common zebras that set the ball rolling. Then the gravy’s followed. The gravy’s can stay without water for long period, but not the common ones. But when one group decided to go to the river, the rest followed even though they may not have been in need of water. While both species were peacefully grazing, they were all mixed up. It was difficult to pick out a common zebra from the group.

To a non-trained eye, they were all zebras. Black with white stripes or white with black stripes. But immediately common zebras made for the direction of the river, others of the same kind who were in the midst of the gravy’s zebras squeezed through the group and joined the common zebras. Soon there was a long line of the zebras heading to the water. The common zebras leading the way while the gravy’s tagged behind. To see the animals organising themselves into distinct groups of same species was very exciting. They were responding to a law or regulation that governs their social integration.

All effective societies must have their rules, laws, conventions and codes of conduct, sets of working principles that each member knows, understands, and for most part, abides by. Wasps advertise these rules chemically. The various members of the colony, with their allotted socio-economic role as males, workers or queens, possess a complicated system of scent markings that act as “calling cards” to others of the same species. Sticky drops of member-specific chemicals secreted by a gland in the wasp’s abdomen will identify each individual and will be recognised by the rest.

It is not unlike the process operating in ant communities should a member of another colony arrive suddenly in the nest. The host ant knows immediately whether the newcomer is a friend or an enemy. However, there is one curious difference. Whereas wasps secrete their own self-identifying pheromone, the acceptability chemical among the ants appear to be distributed by the queen in the colony. In a series of clever experiments done by a scientist – Dr Bert Holldobler – it was established the queen ants endows her own daughters or indeed any other chosen worker with the necessary chemical marks that tells the soldier ants that those individuals are protected by the queen and should not be attacked. In fact, so powerful is this chemical mark of “belonging” that it can override the bonds of kinship. The workers endowed by the queen with this mark of identity may even attack their own sisters that have been reared in a different nest and did not get the mark.

Bees too use chemical messengers in order to establish their social acceptability. Some species of bees that live in very small, quiet societies of only about six individuals, one of the group is appointed as “immigration officer”. It sits at the entrance to the nest and only allows in those bees that secrete the necessary passport pheromone. The guard bees must be able to remember each of their fellow’s odours individually, in order to tell when an interloper is trying to get into the hive without invitation. They can go out and forage within the same locality, but once back to the hive or a nest, a visa must be scrutinised.

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