In my last column I left you wondering what was going on with the zebra data from Hadza kill sites. Were they employing strategies to conserve game populations? The dry season data would appear to confirm this: Hadza were taking mostly older adult males. But data from kills at other times of the year was not following the same pattern.
So what the hell was I missing? Sampling error? Granted, they killed animals at a higher rate during the dry season than at other times of the year, but there was also a longer time to hunt and take game. That didn’t seem to account for the discrepancy. To make a long story short, I began to look at the relationship between zebra age, sex and behavior, as well as Hadza hunting methods and time of year. Turns out there was a subtle, but significant relationship between all these factors.
Remember, I said that Hadza encounter hunt pretty much every time they leave the village. A Hadza hunter always has his bow with him and even if he’s just going over the next ridgeline to visit a neighboring village, he is always scouting for game and will take every opportunity when he sees it to stalk and shoot if possible. Although this type of hunting is always occurring, during the dry season it is surpassed in frequency by employing an ambush hunting strategy. There’s a good reason for this. There are no permanent water sources where the Hadza live and they rely on waterholes to supply their needs. During the wet season (and most of the year) this isn’t a problem: water is everywhere. As the dry season progresses, however, water dries up and only a few waterholes remain on the landscape toward the season’s end. Sometimes the Hadza have to move camp frequently to be situated near the next available waterhole. Camp sizes also increase as more and more Hadza are forced to congregate around the few remaining waterholes. In many ways, the dry season is probably the toughest time for the Hadza.
But every cloud has its silver lining. The scarce water impacts the Hadza, but it also makes the game animals in the area highly predictable in their movement – game also need to be where the water is. Hadza hunters know that, during this time, they don’t have to chase the game like other times of the year – all they have to do is let the animals come to them. Ambush hunting at waterholes is a highly effective strategy and most Hadza game kills during the year occur at this time.
Hadza hunting strategies aren’t the only things that change from seasonal circumstance. Turns out zebra don’t behave the same way at waterholes either. Typically, there are two types of zebra herds on the landscape: a dominant male with a harem of females and young, and bachelor herds comprising just males. While during most of the year, these herds can be encountered randomly across the landscape, when they are forced together at a few waterholes during the dry season, their behavior changes. The dominant male, females and young tend to come into a waterhole first, with the bachelor males milling around the outside, waiting their turn. This means that, all things being equal, bachelor males tend to be interposed between the female herd and the Hadza hunters in their blinds.
Now, were Hadza to employ a conservation minded strategy, where the intention is to take only males, this could theoretically be accomplished. Hadza hunters could wait from concealment until they are sure a male is close and presenting a good opportunity for a shot. But that is not what happens hunting with bows and arrows at a waterhole in East Africa. Animals are already skiddish and wary while drinking because waterholes are good places to get ambushed in general. Not just from Hadza but from lions, leopards and other carnivores as well. The animals are not going to linger at the water, and Hadza do not have the luxury to be choosy about what they take. The procedure is to let the game in, then get up and fire a shot quickly – at the animal in closest proximity a the time. With zebra, during the dry season, at the waterhole, and with Hadza shooting quickly from ambush, most of the time that prey animal is going to be an older adult male.
In contrast, during other times of the year, zebra herds are dispersed, Hadza employ encounter hunting methods and a zebra of any age or sex could end up being the target. In fact, my observations suggest that encounter hunting during the wet season would be the best time to employ a selective, conservation-minded hunting strategy. Many Hadza hunters informed me that it’s actually easier to sneak up on animals during the wet season since the vegetation is wet and a hunter can move quietly, unlike trying to stalk with dry, crackling leaves and branches underfoot during the dry season. Hadza should have much more of an opportunity to selectively cull zebra during the wet season.
But they don’t. As I pointed out, zebra kills outside of the wet season are much more randomly distributed and reflective of chance encounters with all zebra, regardless of sex or age class. In spite of the fact that this is the best time to selectively target animals to aid in long term population viability, the Hadza are not doing this.
While there is an appearance of Hadza selectively taking zebra to meet conservation goals, it is not the result of intentioned conservation efforts. It is nothing more than contingency: the intersection of hunting method, time of year and prey behavior that results in hunted populations that look like they’re being controlled. Nor should we be surprised by this. Like most aboriginal hunters, the immediate goal is getting meat. Aboriginal hunters are thinking about surviving today….tomorrow… maybe even into next week. Long term conservation efforts are not a high priority….if indeed they are even on the “to do” list.