Giving up trash for Lent: How a human custom forces hyenas to hunt

ResearchBlogging.orgAll over the world, the expansion of urban areas and other human activities has pulled the natural prey base out from under many ecosystems and brought large predators in close contact with people and the resources they can provide – livestock, garbage, unattended pets, etc.. Many predators will take advantage of these food sources, often leading to human-animal conflicts (see wolves in the western U.S., lions in Africa and a range of others). Sometimes, though, humans and wild carnivores will become fairly friendly neighbors.

On the Horn of Africa, spotted hyenas (Crocuta crocuta) have adapted well to dense human populations, and the two species have a unique relationship that benefits both of them. The hyenas almost never attack people and mostly leave their livestock alone, preferring to scavenge on waste and refuse from homes and businesses. The hyena’s iron stomach helps them fit in well here, and they can choke down almost any organic matter they find at the dump – from leftover porridge, to feces, to putrid, anthrax-infected carcasses. The people aren’t exactly thrilled with the hyena presence, but many villages and towns tolerate them as walking garbage disposals. The locals call them “municipal workers,” and refrain from harassing or killing them.

Every year in the spring, this arrangement collapses when members of the Ethiopian Orthodox Tewahedo Church celebrate the fasting period of Lent. For 55 days leading up to Easter, Ethiopian Christians abstain from meat and other animal products, which causes a slow couple of months for the local butchers, and a dearth of carcasses at the dumps.

Without the fat of the land to live off of, what’s a non-Christian hyena to do? Gidey Yirga from Ethiopia’s Mekelle University and colleagues from Africa and Europe observed the animals during last year’s Lent and found that thy turn to hunting instead. Despite their reputation as strict scavegners and opportunists, hyenas are formidable, efficient hunters. Stalking alone or in packs, they favor large prey (150-400 pounds) and a lone adult hyena can take down an animal four times its own size. In East African ecosystems where scavenging opportunities are rare, they hunt and kill 60–95% of their food.

Last spring, Yirga and his team went to three different sites around the city of Mek’ele and collected all the hyena droppings they found on the first day of Lent, the last day of Lent and 55 days after that. Several months worth of dropping gave them a glimpse of what the hyenas were eating before, during and after the fasting period. There isn’t much to be found in a hyena turd, since they can digest pretty much all parts of their prey except hair, hooves and a few inorganic components found in bones. It was enough for the researchers to go on, though, and they compared the hair from the 553 droppings they found to hairs from a reference collection to ID the animals the hyenas had been eating.

The scat studying revealed that before and/or after Lent, most of the hyenas’ diet is made up of goat, sheep, horse and cow – usually scavenged waste parts. While humans are fasting, though, the hyenas scavenge less (while the butchers’ supply dried up, the local veterinary school still provided some carcasses) and fill the gaps in their menu by actively hunting donkeys. The donkey is a natural choice of prey if an urban hyena has to go after a live animal. They’re the right size and, unlike the other local livestock, they’re not kept penned in in compounds. They’re easy pickings, and during Lent, the hyena’s donkey consumption can double from surrounding weeks.

Faced with a carnivore’s dilemma, the hyenas showed how adaptive they can be to the sometimes strange behaviors of their human neighbors. Yirga’s study is not only evidence of the hyena’s versatility, but also highlights trash as a delicate factor in urban carnivore management. If you give predators an inch, they’ll take a mile, or a donkey, and better waste management would create a less inviting environment for them. In areas where wild carnivores have grown dependent on livestock and garbage for lack of other prey, though, a too-tight lid on the garbage can could thin their numbers and have an ecological ripple effect.

Hat tip to Barbara J King for bringing the study to my attention. 

Reference: Yirga, G., De Iongh, 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 DOI: 10.1111/j.1365-2656.2012.01977.x

Images: “Portrait of a Spotted Hyena” by Marieke Kuijpers. “Spotted Hyenas, Crocuta crocuta, at carcass of an Impala” by Jerry Friedman. Both used under a Creative Commons License