Hyena scavenging provides public health and economic benefits to African cities

Date:
September 27, 2021
Source:
University of Michigan
Summary:
Hyenas are frequently vilified and often feared. Hemingway once
described the hyena as a stinking, foul devourer of the dead,
with jaws that crack the bones the lion leaves.



FULL STORY ========================================================================== Hyenas are frequently vilified and often feared. Hemingway once described
the hyena as a stinking, foul devourer of the dead, with jaws that crack
the bones the lion leaves.


==========================================================================
But a new study concludes that spotted hyena scavenging provides
significant public health and economic benefits to the African cities
they roam.

In a study conducted in and around the Ethiopian city of Mekelle,
home to 310,000 people and 120,000 livestock animals, a University of
Michigan conservation ecologist and two colleagues found that spotted
hyenas annually remove 207 tons of animal carcass waste.

Mekelle is the capital of northern Ethiopia's Tigray region. The
carcasses of livestock animals that are slaughtered for food there,
or that die naturally, are often dumped at the local landfill or on
roadsides, where hyenas feed on the waste. The researchers wanted to
know whether hyenas -- by removing this waste from the environment --
might also prevent pathogens from jumping into people and livestock.

They determined that hyena scavenging annually prevents five infections
of anthrax and bovine tuberculosis in Mekelle residents and 140 infections
in cattle, sheep and goats. This disease-control service potentially saves
the city $52,000 annually in treatment costs and livestock losses avoided.

The study, published online Sept. 26 in the Journal of Applied Ecology,
is the first to quantify the public health and economic benefits of
scavenging by spotted hyenas.



========================================================================== "Yes, the effects are modest. Even so, this study totally upends
the traditional narrative around hyenas -- that they are a nuisance
and should be removed," said U-M's Neil Carter, senior author of the
study and an assistant professor at the School for Environment and Sustainability. "This is an important contribution to a growing body of
work that highlights the benefits of predators and scavengers, rather
than focusing only on their costs to humanity." The authors emphasize
that these sanitation and disease-control services are particularly
valuable in low-income and rural areas. In Mekelle, the scavenging
behavior of hyenas advances three U.N. Sustainable Development Goals:
ensuring good health and well-being, providing clean water and sanitation,
and promoting terrestrial biodiversity.

To estimate the benefits of spotted hyenas, the researchers examined
their feeding habits and the population size around Mekelle. During
the daytime, the Mekelle hyenas rest at sites outside the city to avoid
human disturbances; they come into the city at night to feed.

The field data were collected and analyzed by study lead author Chinmay Sonawane, a former student of Carter's who is now a doctoral student at Stanford University.

Those data were integrated into a disease transmission model used to
predict the number of anthrax and bovine tuberculosis infections arising
in humans and livestock from infected carcass waste, as well as the costs associated with treating those infections and losing livestock. The
researchers compared these public health and economic outcomes under
two scenarios: hyenas present and hyenas absent.



==========================================================================
"In comparison to the large cattle enterprises in the Global North,
the benefits that we found are quite small," Sonawane said. "However,
losing even a single cow to anthrax or bovine tuberculosis can cause significant financial stress to cattle owners in Ethiopia, who tend to
own much smaller herds of cattle than cattle owners in other parts of
the world.

"In addition, we only estimated the benefits accrued from hyenas within 5 kilometers of the city. It is very, very likely that hyenas much further
than 5 kilometers are coming into Mekelle and consuming even more waste."
For Sonawane, the fieldwork involved spending nights at the Mekelle
landfill and recording the number and type of animal carcasses (mostly
cattle, horses, chickens, sheep and goats) available to the scavengers.

He counted the hyenas and watched them feed, using night-vision binoculars
that operate at infrared wavelengths. The black-and-white photos and
video clips he captured are haunting: the eyes of the hyenas glow with
an unearthly fire.

The study authors determined that an individual Mekelle hyena annually scavenges about 2,100 pounds of carcass waste around the city. For
hyenas feeding at the landfill, horse carcasses accounted for about 80%
of that total, while poultry waste was the most frequently consumed type
of animal carcass waste.

The researchers estimated a population size of 210 hyenas around
Mekelle using "call-in surveys." This field method involved broadcasting prerecorded hyena distress calls with a 45-watt megaphone from the top
of a vehicle at five locations around the city. During each hour-long
survey, the researchers counted the number of hyenas attracted to the
sounds and visible with the night-vision binoculars.

Given the consumption rate and the estimated population size, the Mekelle hyenas were expected to annually remove 207 metric tons of animal carcass waste, which is 4.2% of the total animal carcass waste thrown away by
residents and businesses.

Waste generation in Mekelle is expected to increase with the exponentially growing human population there, Carter and his colleagues wrote: "Given
the financial constraints on waste collection and disposal services,
sanitary conditions are expected to deteriorate further." Hyena scavenging
may, therefore, be even more valuable in the future.

The authors note that the benefits of hyena presence must be weighed
against the costs. A 2011 study reported 10 nonfatal hyena attacks on
humans annually in Mekelle, along with an estimated economic loss of
$2,928 from 33 fatal attacks on cattle and small ruminants annually.

To preserve the public health and financial benefits provided by hyenas
into the future, nonlethal management actions that minimize risks and
enable hyenas to coexist with humans are necessary, according to the
authors.

"By maintaining the hyenas' access to waste, human-hyena conflict can be mitigated in Mekelle, and the sanitation and disease control benefits
provided by hyena scavenging can be preserved or even increased,"
they wrote.

But excluding hyenas from scavenging animal carcass waste may compel
them to hunt livestock and could increase human-hyena conflict, as a
previous study in Mekelle has shown.

The other author of the study is Gidey Yirga of Mekelle University. The researchers thank Haile Gerigis, Mekelle University and the Norwegian
Agency for Developmental Cooperation for providing field support and the
Office of Undergraduate Research and Fellowships at Harvard University
for providing financial support.

========================================================================== Story Source: Materials provided by University_of_Michigan. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Chinmay Sonawane, Gidey Yirga, Neil H. Carter. Public health
and economic
benefits of spotted hyenas Crocuta crocuta in a peri‐urban
system.

Journal of Applied Ecology, 2021; DOI: 10.1111/1365-2664.14024 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210927110508.htm

--- up 3 weeks, 4 days, 8 hours, 25 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)