It's springtime in the northern hemisphere, which means that Christians are giving up meat for Lent, Jewish people are eating matzah instead of bread for Passover, and spotted hyenas (Crocuta crocuta) are replacing their regular meals with donkeys, in honor of the Ethiopian holiday Abye Tsome.

Hyenas will eat just about anything organic. They'll chow down on mammals, birds, fish, and reptiles. And it doesn't matter whether those critters are living or dead. Or rotten. Or infected with anthrax. Hyenas are also known to dine on garbage and dung. This doesn't mean they're not skilled hunters. In fact, in the Maasai Mara ecosystem in Kenya, they hunt as much as ninety-five percent of their food. But when there are humans around, it is perhaps a better strategy to rely on scavenging.

The neighborhoods around the northern Ethiopian regional capital of Mekelle, is a very poor area. Despite the high levels of poverty and the scarcity of resources, inhabitants of the region adhere strictly to the religious restrictions pertaining to meat eating. "The remains of slaughtered animals and all redundant pack animals are always left at the nearest convenient site, usually simply just outside the people's compounds," Yirga writes.

That all changes, though, during the 55 days leading up to Easter, when members of the Ethiopian Orthodox Tewahedo Church give up meat for a holiday known as Abye Tsome or Hudade. Biologist Gidey Yirga and colleagues wondered what effect the reduced supply of meat during Abye Tsome might mean for the hyenas that rely on human table scraps to survive the rest of the year.

They collected 553 samples of hyena scat and analyzed the hairs found inside each sample to determine which animals made up each hyena's last feast. While the hyenas dined on all manner of beast prior to and after the holiday - sheep, horses, cattle, goats, and more - they mainly fed on donkeys during the fast period itself. Yirga notes that, unlike other livestock, "donkeys are kept outside the compound at night, and weak donkeys are abandoned altogether, which makes them a relatively easy food source."

In the areas around Mekelle, hyenas rarely attack humans, and Yirga reasons that this is because hyenas don't feel threatened. Humans appreciate their work: hyenas are regarded as "municipal workers." In fact, hyenas are the most efficient janitors on the campus of Mekelle University, where they scavenge the carcasses of dead animals at the veterinary college.

An ecosystem can be like a precariously balanced house of cards. Most of the year, the hyenas and humans around Mekelle live in relative harmony. Humans toss out their leftovers, and hyenas gobble them up. But the religious fasts leading up to Easter disrupt hyenas' menus, causing them to alter their foraging strategies by hunting donkeys. The loss of donkeys to hyena predation, in turn, causes problems for the humans who rely on donkeys for collecting fresh water, working on farms, and carrying produce and goods to and from the markets. It's a problem for humans, but only for a few weeks each year.

Other communities deal with potential livestock losses in more aggressive ways. In southern Ethiopia, for example, lions (Panthera leo) are pre-emptively killed anytime they get too close to humans or livestock. As a result, the amount of lions in the ecosystem has decreased, despite the fact that the ecosystem is fully capable of sustaining viable populations of lions (and hyenas, too, for that matter). "We found only two lions and six hyenas," in Nechisar National Park, Southern Ethiopia, Yirga said, due to "conflicts with the communities living inside and adjacent to the national parks." This is partially due to the killing, but also probably because the remaining lions and hyenas have learned to avoid those villages where they might be killed.

These are both examples of other carnivores altering their behavior due to changes in human behavior, but the results couldn't be more different. In the north, villagers tend not to lose livestock to predation because hyenas scavenge instead (except for several weeks in the springtime). In the south, villagers tend not to lose livestock to predation because many of the big predators have been driven to extinction or scared away.

This leads me to speculate: could sharing meat with lions in the south, as is done with hyenas in the north, result in improved human-lion relations, decreased losses of livestock due to predation, and an overall healthier ecosystem?

Yirga, G., De Iongh, H.H., Leirs, H., Gebrihiwot, K., Deckers, J. & Bauer, H. (2012). Adaptability of large carnivores to changing anthropogenic food sources: diet change of spotted hyena (Crocuta crocuta) during Christian fasting period in northern Ethiopia, Journal of Animal Ecology, no. DOI: 10.1111/j.1365-2656.2012.01977.x

Image: Hyena in the Serengeti, gnawing on the skull of a gnu via Flickr/appenz

For more perspectives on this research, see:

Giving Up Trash for Lent: How A Human Custom Forces Hyenas to Hunt by Matt Soniak

Hyenas Fast During Lent Too by Elizabeth Preston

In run-up to Easter, fasting Ethiopians force hyenas to kill donkeys by Ed Yong