BCI and partners are working to develop a plan for sustainable guano extraction in Mozambique’s caves.

Photo: Piotr Naskrecki, Ph.D.

BCI and partners are working to develop a plan for sustainable guano extraction in Mozambique’s caves.

Photo: Piotr Naskrecki, Ph.D.

Guano Guidelines

Setting standards for sustainable resource extraction in Mozambican bat caves

By Annika S. Hipple

Deep in a narrow Mozambican cave, Natalie Weber suddenly emerged into a larger, hotter, more humid space surrounded by tens of thousands of flying bats. It was late March, and Weber, Bat Conservation International’s (BCI) Strategic Advisor for Endangered Species—Africa, was in Mozambique to assess the status of bat maternity roosts in nine different caves and develop a plan for sustainable extraction of bat guano.

Ultimately, the goal is to establish standards for sustainable guano extraction in caves.

Accompanying her were a prospective guano miner and staff from nearby Gorongosa National Park, which has buffer and transition zones that include caves that are home to a number of bat species. One of these species is Macronycteris vittata, the striped leaf-nosed bat, which is classified as “Near Threatened” by the International Union for Conservation of Nature.

BCI, Gorongosa scientists, and the GuanoMoz team take a break while documenting one of the caves slated for bat guano extraction

BCI, Gorongosa scientists, and the GuanoMoz team documenting one of the caves slated for bat guano extraction.

Photo: Piotr Naskrecki, Ph.D.

Balancing resources

An essential food source for various invertebrate species, bat guano is also a popular fertilizer. One challenge for BCI and its partners is determining the rate at which bats produce guano versus the rate at which it is being extracted and how its removal influences a cave’s temperature and humidity. The two “hot caves” identified during the study were excluded from the extraction to protect the bats that use those caves. The caves would likely be impacted by guano extraction since the process may increase the size of the cave’s opening. Once extraction has begun, staff from Gorongosa will visit the caves regularly to check monitoring equipment and any impacts of guano extraction on the caves.

The opportunity to monitor these particular caves presented itself when the guano mining company GuanoMoz requested assistance in implementing scientists’ recommendations for minimizing the impact of the extraction operations on bat populations.

One challenge for Bat Conservation International (BCI) and its partners is determining the rate at which bats produce guano versus the rate at which it is being extracted and how its removal influences a cave’s temperature, humidity, and, thus, bat populations.

“As far as we’re aware, this is one of the first times it’s been attempted to figure out if there is such a thing as sustainable guano harvesting,” says Isabella Mandl, Ph.D., BCI’s Regional Director for Africa and South Asia.

Sustainable guano extraction

Determining how much guano can be sustainably removed without affecting the cave ecosystem is critical. “There have been no trials, no studies on this before, so our suggestion would be to go with half of the guano layer first,” Weber says. “Then we’ll see if this works for the bats and everyone. In an ideal world, we would have had 12 months of monitoring data even before the first extraction because we can also expect seasonal patterns.”

“If you take out loads of guano, there’s always a risk of knocking the ecosystem out of balance. We don’t know to what extent. It’s a unique opportunity, but we have to be very aware of the reality that guano harvesting will have an impact. This project allows us to figure out what the impact could be and how we could potentially minimize it.”
—Isabella Mandl

Leaf-nosed bats (Hipposideros caffer) emerging from a cave.

Photo: Piotr Naskrecki, Ph.D.

Mandl points out that trying to define sustainability within this context is a challenge. “If you take out loads of guano, there’s always a risk of knocking the ecosystem out of balance. We just don’t know to what extent,” Mandl says. “It’s a unique opportunity, but we have to be very aware of the reality that guano harvesting will have an impact. This project allows us to figure out what the impact could be and how we could potentially minimize it.”

Ultimately, the goal is to establish standards for sustainable guano extraction in caves. “We want to make sure that the conditions to allow for recovery of the guano deposits would be protected,” Weber says. “That means we need the bats. We need other organisms that can survive in the caves even though extraction is happening so that the ecosystem stays healthy and intact.”

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