National Zoological Park' Smithsonian Institution' Washington, D.C. 20008 
Creating the Nation's first BioPark 
Letter from the Desk of David Challinor 
April 1992 
From 26 February to 1 March, twelve members of the Zoo's National 
Council visited Panama where they viewed many of the facilities 
of the smithsonian Tropical Research Institute (STRI). Mike 
Robinson, who worked at STRI for 20 years before coming to the 
Zoo, and I were the joint leaders, and we and the Council members 
observed many fascinating aspects of the research underway at 
STRI. 
Following an evening arrival on Wednesday 26 February, we left in 
a STRI bus about 6:30 the next morning to drive north to Gamboa, 
a road-head town on the Panama Canal about 17 miles from the 
Pacific entrance. At Gamboa we boarded STRI's passenger boat for 
the ten mile trip north to the well-known Barro Colorado Island 
(BCI) in Gatun Lake. BCI and the adjacent mainland peninsulas 
make up the 12,000 acre Barro Colorado Nature Monument 
administered by STRI for the Republic of Panama. 
The Zoo group split into two sections; Mike led one and I the 
other into the forest where both parties saw a multitude of fauna 
and flora. Mike's group visited the huge Kapok tree (Ceiba 
pentandra), the largest tree on the island, and saw the only 
troop of tamarins on BCl. These small monkeys are rare on this 
island because they prefer secondary growth and BCI is now 
virtually all primary growth. Mike's tour group glimpsed the 
small forest-dwelling Red brocket deer, which is secretive, 
solitary and seldom seen. My group was rewarded with clear views 
of a troop of black howler monkeys, agoutis and coatis, plus 
scores of birds, many of which were "lifers" for George Didden 
and myself. 
The next morning, Friday, we drove to the edge of a forest on the 
outskirts of Panama city where Alan Smith, a STRI botanist, 
demonstrated how he studies the forest canopy from a 4-person 
gondola attached to an 80-foot high T-crane, a building 
construction device adapted for research by STRI. Those who 
chose to ascend to the top of the forest in the gondola with Alan 
were able to see how trees and woody vines compete for sunlight. 
Both need sunlight to grow, but trees have to support themselves 
structurally. Vines do not, and thus they concentrate their 
energy on longitudinal growth using the host tree for support. 
The vine cannot be too successful and kill its host by completely 
blocking access to light, because if the tree dies and falls, the 
vine is lost, too. 
1889-1989 
.....for the advancement of science and 
the education and recreation of the people." 
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April 1992 Page 2 
Some tree species were conspicuously devoid of vines, and using 
the gondola as an observation platform, Alan and his colleagues 
analyze the mechanisms by which some trees are able to keep vines 
from growing on them. Trees have several strategies to compete 
with vines. For example, in certain species the tree itself is a 
host for arboreal ant colonies. Whenever vines start encroaching 
on the tree's crown, the ants nip off the vine tendrils, thus 
preventing the invader from gaining a foothold. Other tree 
species seem to produce chemical compounds that discourage vines 
from coming into contact with their leaves or bark. 
From the forest canopy we went to STRI's new research facility 
where we met with scientists who patiently described their 
research. One colleague, Stan Rand, has been studying frogs for 
most of his career . He described how on a given local pond, 
shortly after the start of the rainy season, there could be as 
many as 15 different frog species whose males would each call 
females in their own distinctive way. To human ears the mixed 
chorus sounds cacaphonic, but to the frogs the sounds are 
orderly. By recording the calls of each species and displaying 
them on a sonagraph, Stan found very little overlap in the 
intensity and frequency of the different species' calls. Thus a 
female frog could easily isolate the courtship call of her 
conspecific male. 
Stan also described one frog species that has a standard 
monosyllabic call when a single male calls from a pond edge. 
However, if more than one male of this species calls, then each 
adds to its regular call an extra syllable that sounds like 
"chuck." The more "chucks" added up to a maximum of six, the 
more likely the frog is to lure a female. But at what a cost! 
The more chucks, the greater the likelihood that the 
extravagantly serenading male will be caught by a frog-eating 
bat, which echolocates with particular accuracy on the "chuck" 
sound. As most of us know, every success has its price. 
After a delightful lunch with some of the STRI scientists, we 
visited the breeding facility for pacas established by Nick 
Smythe. Pacas are the size of a very large rabbit and are 
nocturnal, solitary, forest-dwelling rodents. Their coats are 
dark red with parallel rows of white spots on their flanks. 
Unlike its diurnal equivalent, the agouti, the nocturnal paca 
lacks a strong scent and therefore makes for declicious eating. 
Hunting pressure has made pacas rare locally. until recently 
attempts to breed them for domestic consumption have failed 
because pacas normally live only in pairs and are aggressively 
territorial. When placed together, pacas often fight to the 
death. After more than a decade of work, Nick Smythe has 
overcome this aggressive action of the pacas, and we saw pens 
full of these rodents lying together like rabbits or guinea pigs. 
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April 1992 Page 3 
Nick's project is part of a long-term STRI effort to find ways of 
exploiting the tropical forest for useful local products without 
at the same time destroying it. 
We spent the afternoon at STRI's marine laboratories on Naos and 
its adjacent islands, which are connected by causeways to the 
mainland. There we met John Christy, who told us about his 
studies on fiddler crab courtship and mating. The male's large 
claw is used for courtship and for fighting other males for 
burrows ("nests") to which females come for mating and breeding. 
Fiddler crabs see tall objects on the horizon very well. They 
rapidly detect predators and, if they are away from a burrow, run 
to grass or roots that provide cover. They see objects on the 
ground very poorly. Crabs find their way back to their own holes 
by memorizing the steps they took in each direction. This memory 
map is of little use to females when they wander in search of 
mates . In Panama's tidal flats, courting males of some species 
build little towers of mud next to their holes. These towers are 
very attractive to females both when they are searching for mates 
and when they are escaping predators. Even females of other 
species that do not build towers will run to them for protection. 
Courting males benefit from building towers because females are 
attracted to them as they are to grass and roots when females run 
from predators. I wish that I could inclUde in this letter all 
the other fascinating research accounts we heard, but space 
precludes this option. 
On Saturday, our last full day, we cruised in the Bay of Panama 
on STRI's R/V Benjamin. We circled Taboga Island about six miles 
offshore where we hoped to visit the pelican rookery. The birds 
had not yet started to nest, however, because the southwest trade 
winds had not blown hard enough to push the Bay's nutrient-rich 
deep water to the surface. The rich water in turn triggers an 
explosion of the fish population which provides the pelicans 
plentiful food to enable them to start nesting. Instead of 
hiking to the empty rookery, we swam at the beach below the small 
fishing village on Taboga. 
This trip to Panama was such a success that I am planning one for 
interested members of the Zoo's Council next year. At the end of 
March I go to Mt. Hopkins in Arizona, a 9,000' mountain in the 
Coronado National Forest, about 40 miles south of Tucson. The 
Smithsonian operates the United States' second largest optical 
telescope on the summit of this peak. We could visit the 
telescope as well as the surrounding 4,000 acres which the 
Smithsonian manages; it is full of wild turkeys, javalinas, 
coatis, and a host of birds inclUding trogons. If arrangements 
April 1992 Page 4 
can be made for a trip in March 1993, I will notify all members 
of the National Council and the Director's Circle well in 
advance. 
Before closing this letter, I must clarify a clause in my March 
letter: "chimpanzees share 98% of our [human] genetic 
material .... " Those portions of the human and chimpanzee genes 
that have been studied so far have shown a surprisingly similar 
identity (about 98%). However, only a very small part of the 
total human genome (maybe 5%) has been mapped, and work on the 
chimpanzee genetic code is even less complete. ThUS, if these 
very preliminary mapping results of human and chimpanzee genes 
are sustained by further analysis over the next few decades, my 
statement about the closeness of the genetic relationship between 
these two primate genera will be more supportable. 
The Spring meeting of the National Council will be at 9:30 a.m. 
on Friday, April 24, 1992 in the Board Room of the Zoo's 
Education and Administration Building. Please note the agenda 
attached. I look forward to seeing many of you then. 
David Challinor 
Science Advisor to the secretary 
(202) 673-4705