The fifth Howler Monkey census at the Smithsonian's Barro Colorado Island research station in Panama, organized by Katie Milton, professor in the department of Environmental Science, Policy & Management at the University of California, Berkeley, revealed that monkey numbers have not changed significantly since the first census 33 years ago.
Long before dawn on March 19 and 20, Katie Milton and a group of stalwart volunteers, each armed with flashlight and compass, spread out into the jungle to find 35 predetermined listening stations marked on their maps of the island.
Just before sunrise, howler monkeys launch into a chorus of howls, roars and barks. From 5:15 am until 6:30 am, each volunteer recorded the time and direction of these vocalizations and estimated the distance to each group that they could hear from their stations. As they walked back to the lab in the early morning light they noted locations of any monkey groups they saw.
"It amazes me that volunteers want to get up at 4 am to walk through the dark forest alone for an hour or morebut it is a thrill when they hear that first howl and know the dawn chorus is beginning," said Katie Milton.
Lines drawn on a map from each station toward the compass angle of the observed sounds intersect, marking the estimated location of each group. Based on this technique called triangulation Milton estimated that there are 60-70 groups on the island. By multiplying the number of groups by the average number of individuals in a groupbetween 17 and 18 monkeys she concluded that there are roughly 1200 individuals in fairly evenly spaced groups.
Census volunteers always include internationally known ecologists: Smithsonian staff scientists and visiting scientists as well as current students and fellows. Barro Colorado's game wardens and two Panamanian national forest police manned some of the most inaccessible listening stations. Eight highly-motivated students
|Contact: Beth King|
Smithsonian Tropical Research Institute