The Demise of the Pig-Tailed Squirrel Monkey

This is a story I wrote many years ago, now.  Since I have become a parent, I look at things from the other angle – toddlers can be as entertaining as television and if I didn’t have a television, well, I’d want some more amusement!….

 

 

 

The Demise of the Pig-Tailed Spider Monkey

 

            Ladies and Gentlemen, I will not be giving today a normal seminar with an introduction, methods, results or conclusions.  The facts of my studies are too tragic to be subjected to such objective treatment, and neither my theories nor discussion stem from experiments, for as you will see, such experiments as could be designed are no longer possible.  But the lessons learned from my work may help in other circumstances, and have behavioural anthropological interest in themselves.  

            Ladies and Gentlemen, I have bad news.  The pig-tailed spider monkey is dead.  Though two individuals do still survive, the species is effectively extinct, since they are both male.  It is my duty today to describe the demise of this species.

            This little-known monkey was only discovered in 1968 in a valley of central Brazil.  Three family groups, totalling fifty seven individuals, were found when the valley was opened up for logging by the government.  The population has been studied continually since 1970, when the surrounding valleys were searched unsuccessfully for other groups.  Habitat destruction had presumably been responsible for the expiration of the monkey in other areas.  A small research group with little funding was stationed in the valley to study the existing groups and evaluate the need and probable success of a captive breeding program.  International pressure reduced the logging to 10% of the valley surface, but the truth of the case is that habitat destruction has not been the final straw in the extinction of the pig-tailed spider monkey.  Before I go into that, however, I would like to detail the life history and vital parameters of this unfortunate species. 

            The pig-tailed spider monkey, Ateles colaporcinus is a medium sized new world monkey which usually measures between 70 and 80cm with the tail accounting for half of this.  The tail, which is of course prehensile, is relatively shorter than other spider monkey species and tends to curl up tightly when not in use: hence the name.  It feeds on fruit, some plant shoots and leaves, bird’s eggs, insects, and some small mammals.  The sexes are not very dimorphic in size, which has a bearing on the problems it encountered. 

            All individuals were identifiable – from their pelage markings at first, then later by transponder implanted under the skin of the shoulder.  We had no incidents of trapping related mortality.  The monkeys had quickly grown accustomed to our presence and even proximity, readily accepting bait bananas.  They were perfectly calm while being handled and sedative was not required. 

            We collected all individuals after death and attempted to age them using cementum layer analysis, which proved impossible, and so the age structure of the original population is somewhat sketchy.  All infants have been followed since then, so that in 1980, the complete population structure was available.  As you can see from the graph, there were 20 infants, birth sex ratio being equal.  Mortality in the first year was nearly 50%, mainly due to abandonment and accidents.  Survival thereafter was high, though significantly fewer males survive to age three. 

            Females have been known to live for up to twelve years, males for eight, though the surviving male is now eight and shows no signs of aging: at least in terms of dental wearing, his incisors and canines being still quite sharp.  Females become sexually mature at age two, and normally give birth to singletons every year after a gestation of some five months.  Twins are born in approximately one out of every ten births.  Triplets are unknown, but perhaps occurred occasionally.  Average fecundity from 1980 to 1984 was 71%, but decreased sharply in later years.  Females tended not to bear young after the age of seven, though one eight-year-old did once. 

            The monkey, which had become so accustomed to the researchers, soon became habituated to the handouts of bananas which the guards fed them.  It is a highly intelligent monkey and easily trained to perform tricks, which the Govt. workers insisted on doing, despite our disproval of the practice.  This led to the monkeys remaining near to the guard huts for most of the day, and only retreating at nightfall to the trees. 

            Logging was stopped completely in 1984, when the Brazilian Government made the area a protected zone, in order to negate the need for captive breeding off site.  The valley was patrolled by Park Rangers and soldiers when necessary, to keep out loggers, mining prospectors and also any peasant slash and burn farmers or native tribal Indians.  The guards took a great interest in their subjects.  Unfortunately, it was their very protection which has been the root of their destruction. 

            At this point I must confess to you our culpability in what followed.  We have been deficient: there are excuses but they are not sufficient, and I personally take responsibility for this tragedy.  It was, in one way, advantageous to have the monkeys habituated to the huts and people, since it made the study of their social behaviour easier, and meant that any translocation that should be necessary were the government to rescind protection of the valley (a real possibility) that much easier.

            The first year after the valley was given protection and the government workers arrived, the birth-rate dropped from 77% to 23%.  We were not unduly worried, for there had been years with low births before.  We attributed it to a low fruit mast and allowed the guards to feed them more liberally. 

            When the following year, births were even lower at just 10%, we sounded the alarm.  The adult males were re-trapped and sperm samples taken, but all were normal.  The food was checked and seemed fine, though to be sure females were not beneath the threshold weight for conception, we added more fats.  We were reluctant to capture the females in case stress might further lower their fecundity. 

            The next year, no young were born, and females were weighed, but body weights were not significantly different to those recorded in 1980 when transponders were inserted.  In fact, the mean body weight was non-significantly higher, probably due to the food additives and the lack of active foraging.  We hypothesised that a protein deficiency may have been causing prenatal mortality, as fewer birds-eggs and small mammals were eaten since the monkeys spent so little time foraging in the canopy.  There were many insects around the camp, but nevertheless, we provided dog food and insects caught during fumigations for species diversity work in other areas. 

            The birth-rate did not recover next year and we were aware that we were in crisis, but for various reasons, we found ourselves powerless to alleviate the situation.  After eliminating other possibilities, we came to the conclusion that the reason, Ladies and Gentlemen, thought it may be startling, perhaps difficult to believe and definitely the first recorded case of its kind, for the loss of this species was due to lack of sufficient reproduction as a result of exposure to television. 

            I hope that you will bear with me for a few moments while I explain how we have come to this very surprising conclusion. 

            Their interest in television was startling.  At first we presumed they were merely imitating the guards, while waiting for handouts, and that may indeed have been the case initially.  However, when we insisted the monkeys be fed outside the shelters, they remained inside when not actually eating, and even began to take food directly from the outside feeding trays to the television set.  Since we could not force the guards to stop watching television, and preventing the monkeys from entering the shelter (open on three sides) was practically impossible, we had no choice but to allow the situation to continue. 

            I won’t go into the viewing habits of the monkey, but it was noticeable that music programs and chat shows were watched most attentively.  Offers of food were more frequently rejected during these than during films or the news.  Females seemed more interested than males: another fact that has great bearing on proceedings.

            The fact that television might be the root cause was so astounding that it was scarcely considered at first.  We had witnessed matings before, but not many.  We presumed that most occurred in the canopy at dawn, before the monkeys descended to the camps.  Thus we did not believe that mating could have actually ceased.  Nevertheless, we did ask the guards to turn off the television, but they refused.  We appealed to the government, but nothing was done until 1990, by which time the population had fallen to just five individuals: comprised of one young female, two old females and two males.  To test if the television did in fact have an adverse affect, we undertook an intense re-examination of behaviour in relation to the monkeys’ increased use of the area within the camp.  All age-groups and both sexes interacted quite similarly to before the guards’ arrival.  All individuals seemed active, besides their interest in television.  Infants did not play amongst themselves as much as previously, but they were not obese nor had any problems functioning in group social activities, most of which continued as before, but which now were centred around the TV.  Social activities, such as grooming, in fact increased, as a direct result of the decrease in time spent foraging, due to the supplemental feeding. 

            Sexual activity was examined also, both in the camp and in the canopy, by following the families as they went to roost and watching from before dawn using night-vision telescopes.  We found that sexual activity of the monkeys had plummeted.  There were literally no recorded incidences of matings, though there was a slight increase in male – male sexual interaction and harassment of younger males by adult males.  Females were just not interested in males even during oestrus: they allowed themselves to be groomed, but always maintained visual contact with the television and didn’t allow males to mount them, as it distracted their viewing.  The males were physically unable to force themselves upon the females, due to their similar size, especially as females ganged together to repel males who were intent on mating, as it also interrupted their viewing. 

            This brings us to the anthropologically interesting side of this sad course of events.  The monkeys of course, despite being clever, have not made the connection between mating and giving birth.  They didn’t know that their numbers would dwindle without sex: something that humans do.  The observed decline in births, and thus presumably sex, which occurred after the invention and spread of television was not nearly as drastic, though the slow rate of its spread and the initial low coverage also affected this.  It is of course, well known that even now, there are increases in birth-rates after blackouts and power cuts, when the TV is obsolete.  There might have been a more visible reduction in births after the television’s invention, had men not been able to reason that the family relied on sex for its self-propagation. 

            Getting back to the pig-tailed spider monkey, however: the young female only bore two offspring: a male who is still alive and a female who died during her first year.  The mother died last year, having spent her final days watching Brazilian Big Brother and Jerry Springer in Portuguese, without which she resorted to pulling her hair out and other stress related activities.  Nevertheless: we have stored the ova of this female and her daughter and hope to be able to artificially fertilise these with the sperm from the two surviving males and implant the embryos in a related species, although the funding for this has yet to be obtained.  This is the only hope for this species, though we believe that at least, our experience of the demise of this species may serve to help prevent a similar fate happening in other monkeys.  Thank you….

            Now.  Are there any questions from the floor?