Now We Know Where the Monkeys Are!

One of the greatest challenges in saving small and shy endangered species is to discover how many there are out there and where.  Without that simple statistic it’s virtually impossible to design and evaluate an effective conservation program.  We’re thrilled to say that our Brazilian partner organization, Associação Mico-Leão-Dourado (AMLD) recently made great progress in learning where golden lion tamarins (GLTs) are—and are not. 

The attached figure shows the remaining forest fragments in the São João River Basin, Rio de Janeiro State, Brazil, geographic scope of AMLD’s work and home to virtually all remaining wild GLTs.  Although the area of this watershed covers only 1,630km2 (630mi2), the forest is dense and the terrain is either swamp or steep hills.  Tamarins that are not accustomed to the presence of humans—and may have been hunted or trapped—are impossible to count using standard visual methods.  To solve that problem AMLD’s Metapopulation Team (Meta, for short) and colleagues from Norte Fluminense University designed a method to determine GLT abundance using playbacks of tamarin vocalizations.  GLTs respond to and investigate “long calls” from other tamarins in or near their home territory - click here to listen to a long call!  The Meta team played recorded GLT long calls along 200m transects (sections) in every forest fragment larger than 50ha throughout the São João River Basin.  And they used a GPS to map the locations of all detections. This exhaustive and exhausting survey took over a year to complete but was well worth it!  We now know that there are GLT populations in all 7 of the largest remaining forest fragments. 

Using density figures (number of tamarins per ha) for monitored GLT populations it will be easy to estimate the number of tamarins in each forest fragment—with one caveat:  if the Meta team detected GLTs at a particular point it’s pretty certain that a group lives there.  However, if tamarins we not detected at a point it may either be because they chose not to reply, or because they aren’t there.  Using some fancy arithmetic it’s possible to get around this too.


São João River Basin, Rio de Janeiro State.  Colored rectangles show the results of a survey using playbacks of GLT long calls.  Red dots indicate GPS points marking additional sightings of GLTs.