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Count trees, not lemurs, study says

Counting endangered lemurs has been a crucial but painstaking task in the fight to save the species, but could now become much simpler. 

Instead of tallying individual lemurs, researchers can count something far less mobile: trees. This technique—detailed in a paper published by Duke researchers Aug. 30—is a more straightforward method of determining a species' endangered status and can be applied to other plant and animal species potentially facing endangerment. 

“These results are useful as a baseline to monitor species and predict changes in population sizes in the future,” wrote James Herrera, lead author of the paper, in an email to The Chronicle. “For example, with continued deforestation, hunting, and climate change, we can make forecasts of how population sizes may change in the next 50-100 years.”

Herrera, a postdoctoral research associate in evolutionary anthropology at Duke, explained that 16 of the 19 species studied had population sizes greater than the threshold of 10,000 for being at threat of extinction, according to the International Union for Conservation of Nature. The study documented remote areas in Madagascar that had not been previously surveyed. 

Ninety-five percent of all lemurs are currently at risk of extinction. 

Because nocturnal lemurs have been historically difficult to count, the study also shed light on the abundance of previously unstudied species.

However, the field research itself was no simple matter. Herrera explained that a typical schedule involved waking up around 4:30 or 5 a.m., trekking around the Madagascar forests, stopping to rest and repeating the hikes at night.

“Searching for lemurs at night is extremely tough in this environment, with steep muddy slopes and vine tangles to trip you up, while searching with flashlights for the tiny glint of eye shine that reveals the 30 gram house lemurs 30 meters high in the canopy,” he wrote.

The team slept in camps and went without electricity and running water for months. Herrera mentioned that sometimes, they would go hours without seeing a lemur—even in typical lemur habitats.

Despite the difficulties, the model for counting lemurs is an improvement over those employed in the past, he said. Researchers have attempted conducting a “total census”—or simply counting all the lemurs—but this method is difficult due to the rarity of some lemurs and the large scope of regions to be covered.

The results helped determine the threat status of nocturnal species, which had been so difficult to count in the past that scientists were unsure if they were threatened. 

Several species' large observed populations—about one million dwarf lemurs and white-fronted brown lemurs and roughly 500,000 ring-tailed lemurs—surprised Herrera. 

“These numbers suggest good news for the conservation of some lemurs, but that doesn't mean they aren't at risk due to habitat loss, hunting, and the pet trade,” he wrote.

Herrera also added that similar methods could be applied to a variety of plants and animals, from rosewood trees or amphibians to birds and rodents.

As for how Herrera endured the intense nature of the fieldwork, his secret is rooted in his fascination in the relationships between lemurs and their mutualistic food trees. 

“[Small mammals like rodents and tenrecs] are especially important because they are rare, nocturnal and tend to spend much time burrowing through dense undergrowth and underground, making them very difficult to study,” Herrera wrote.

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