Originally published on Medium 05/29/16.
Although lemur populations were not influenced by forest disturbance, we encountered more lemurs (and saw more species) in undisturbed forest.
White-fronted brown lemurs were legion. They would run through our camp, snacking on the fruit in the trees; they would chitter and hoot from the branches above our heads during our lemur surveys. I started to sigh when they were the only things we saw during a survey. I stopped taking pictures.
Then, I read our lemur guide book and got a reality check.
I was sighing at an endangered species. Despite how common they seemed, this social, fruit-eating brown lemur only lives in northeastern Madagascar. Add their limited geographic range to the fact that they are hunted at high rates by locals, and you have an easy recipe for extinction in the near future.
Madagascar: More Magical than the Dreamwork’s Movie (Despite the Lack of Penguins)
By virtue of its size (slightly bigger than Rhode Island), the Makira-Masoala protected area in the northeast is home to hundreds of species. Compared to elsewhere in Madagascar, the number of lemur species in Makira-Masoala is particularly high…as is their extinction risk due to forest loss and hunting.
Despite the number of lemur species found in Makira-Masoala and their threatened status, we had no idea how lemur populations were being influenced by forest disturbance.
We — a research team composed of scientists from the Wildlife Conservation Society, Madagascar program, and Virginia Tech — sought to clarify the lemur situation in Madagascar’s largest protected area.
What Did We Want to Know?
We had two major questions for our study:
- Is lemur density (i.e., the number of lemurs found in a square kilometer) higher in forests undisturbed by logging and hunting, compared to disturbed forests?
- Do we see/detect more lemurs in undisturbed forests compared to disturbed ones?
What Did We Do?
At six study sites spread across the Makira-Masoala landscape, we walked trails day and night, looking for lemurs. Over five years, we walked 500+ miles, saw 12 lemur species, and 1,000+ observations!
We estimated the density for these three species and compared these estimates between our undisturbed and disturbed forest sites. We also determined how many individuals we saw for every kilometer we walked (i.e., encounter rate), and compared these estimates between forest types.
What Did We Find?
Finding #1: There was no difference in lemur density between undisturbed and disturbed forests.
While this wasn’t surprising for eastern woolly lemurs and the small lemurs, which we know are relatively tolerant of forest disturbance, we thought that there would be some difference for the white-fronted brown lemur, because disturbed forests lack the fruiting trees fruit-eaters (like the white-fronted brown) need. We think that this might be due to our undisturbed and disturbed study sites not being that different from each other.
Finding #2: Although white-fronted brown lemur numbers were similar between forest types, we encountered more white-fronted browns in undisturbed forests.
We think that we see less white-fronted brown lemurs during surveys in disturbed forests because they avoid trails due to high hunting pressure. Meanwhile, the small and woolly lemurs, while hunted, aren’t targeted as heavily as the white-fronted brown lemur.
Finding #3: There were lemur species we only saw in undisturbed and slightly disturbed forests.
Although this might be because we did fewer surveys in disturbed forests, we saw twelve species at undisturbed forest sites compared to an average of six species at disturbed forest sites.
We only saw the four critically endangered lemurs — indri, silky sifaka, red and black-and-white ruffed lemurs — at undisturbed and slightly disturbed forest sites.
Finding #4: In really disturbed forest, white-fronted brown lemurs were only seen at night.
At our most disturbed forest sites, we only saw white-fronted brown lemurs during night-time surveys. The white-fronted brown lemur is cathemeral, meaning it can be active both day and night. We think this switch to night-time activity at really disturbed forest sites might be a way to avoid locals, who hunt them.
What Does All This Mean?
Makira-Masoala is Madagascar’s largest protected area and is very important forest for a number of Madagascar’s unique species. Intense hunting pressure and continued forest loss threatens Makira-Masoala’s lemurs. Despite finding no difference in lemur density between undisturbed and disturbed forests, we found differences in which species were present and how often lemurs were seen during surveys.
Our study has answered questions — does forest disturbance affect lemur populations and how? — but it has also birthed new questions:
Is it because of hunting that white-fronted brown lemurs become more nocturnal at really disturbed forest sites?
What do lemur communities look like in really undisturbed forest sites, far from human influence?
What is the threshold in disturbance that causes rare and uncommon species like silky sifaka and red-bellied lemurs to disappear from forests?
In the future, we may learn the answers to these questions. Until then, if you want the best shot at seeing a number of lemurs in the wild, find a patch of undisturbed forest.
In ‘Makira Lessons’, a series in the making, I’ll sum up the main findings of my published Madagascar research — and any bonus unpublishable tidbits— in a way that is accessible to everyone. If you have any questions, feel free to hit me up on twitter or contact me.
The paper that inspired this post is Estimating Encounter Rates and Densities of Three Lemur Species in Northeastern Madagascar (pdf).