Remote sensing and geographic information systems (GIS) technologies are being used to inform conservation efforts for Brazil’s bearded capuchin monkeys, who use stone tools to crack nuts, an extremely rare behavior in the animal kingdom.
Scientists concerned that the capuchins will lose critical habitat as industrial agriculture rapidly expands and intensifies in northeastern Brazil have taken the first step by characterizing the optimal conditions under which the monkeys find stone hammers in the forest and use them to crack the hard shells of palm nuts to get at the meats.
The new study of the behaviors and habitat of these monkeys, “Remote sensing and habitat mapping for bearded capuchin monkeys (Sapajus libidinosus): landscapes for the use of stone tools,” appears in Volume 9 of the Journal of Applied Remote Sensing.
Allison Howard of the University of Maryland Department of Biology and the University of Georgia Center for Geospatial Research, with coauthors at both schools and NASA Goddard Space Flight Center, said the team started by observing capuchins in the study area, a flat, wooded plain punctuated by steep vertical scarps and plateaus.
For three months in 2013, observers tracked one individual monkey at a time for nine and a half hours a day, using a tablet computer with GPS to record that monkey’s activities (foraging, locomotion, social behavior, remaining stationary, self-grooming, etc.) and the animal’s location on a georeferenced satellite image. The geographic coordinates and behaviors of individual capuchin monkeys were recorded 8611 times over 27 days.
Next, a multispectral satellite image of the study area was used to identify land-use and land-cover elements relevant to the movement of capuchin monkeys, such as vertical scarps and areas of human influence.
Spatial distribution of random points visited for field validation in area of study. A true-color composite of the multispectral WorldView-2 image is shown as background.
By developing a normalized difference vegetation index, researchers were able to map the density of vegetation in the study area. Other factors incorporated in the habitat model included elevation and percentages of green vegetation, bare soil, and shadow from spectral mixture analysis.
The study concluded that the most important landscape characteristics for modeling capuchin use of space were distance to areas of human influence (e.g., agriculture and residential areas) and distance to vertical scarps, with elevation and distance to roads also of high importance. The monkeys spent significantly more of their time foraging in dense vegetation, probably because of the abundance of food there, but also possibly because the vegetation provides protection from aerial predators.
The small-scale subsistence farming that has taken place in and around the capuchins’ home range for generations apparently has had minimal impact on the local nonhuman primate populations.
Industrial agriculture, in contrast, involves the clearcutting of large areas of the wooded savanna, application of chemical fertilizers and lime, and intensive irrigation. It is likely to dramatically impact the low-elevation savanna landscape that capuchins prefer.
What’s more, the study found that the capuchins’ most unusual behavior — finding stone hammers and using them to crack open the palm nuts — typically takes place in areas of low elevation and green vegetation.
“These results are important since the rapid increase in large-plot agriculture (involving clearcutting and conversion to monoculture) of the area near our study site and other similar areas in the region may have dramatic effects on the habitat choices of the bearded capuchin monkeys in the near future,” the authors write. While palm nuts are abundant throughout the monkeys’ range, stone hammers are rare, they write. “Previous work has demonstrated that vegetation and terrain are important predictors in finding sites of stone tool use.”
The National Science Foundation and the American Society of Primatologists funded the study.
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