Stone & Henderson: Nominated Pilot Study On Monkeys
The dental students Geoff Stone and Iain Henderson to our knowledge are the first ever scholars to examine the teeth of Barbary macaques. Their efforts were rewarded: The Glasgow University nominated them for a dental award on their thesis: "A Pilot Study to Investigate the Bacterial Load (Streptococcus Mutans and Lactobacillus) and the Buffering Capacity of Saliva from Barbary Macaques (Macaca Sylvanus) Found at Gibraltar's Ape Den and The Middle Hill".
This summer the Gibraltarian Henderson and the Scotsman Stone compared the saliva of the isolated monkeys from Middle Hill to the saliva of the monkeys in Ape's Den. Being vegetarians by nature the Barbary macaques in Gibraltar are fed daily with a total of 125 kilograms of fruit and vegetables and additional barley grains. Yet, the monkeys in Ape's Den have also become used to sweets, crisps and fast food provided by tourists with the bene volens of tour operators, while the monkeys in Middle Hill live isolated from the public and thus follow their natural eating habits.
Stone and Henderson tried to establish whether the unhealthy diet of the pack in Ape's Den has a negative impact on the health of their teeth. Albeit existing, their findings show that the difference is less significant than they had expected. They pointed out though, that due to limited resources they were only able to scrutinise preliminary findings of a total of nine animals and that a broader spectrum of samples would be needed in order to truly determine the impact.
As methods of obtaining the saliva, Stone and Henderson used a sort of sugar free raspberry-flavoured chewing gum, a 'pledgelet'. Ms Kate Henderson, an anthropologist from Notre Dame University, USA, delivered it to the monkeys with a sterile gloved hand. These pledgelets had the purpose to collect the plaque and bacteria from the teeth and had to be chewed on for a minimum of five minutes for validity. After the monkey spit the gum out, it was immediately collected with a sterile gloved hand, put into a test tube and tested in a laboratory.
Stone and Henderson wrote, they observed that only young and sub-adult monkeys were willing to treat the pledgelets as possible food source, while mature and old macaques automatically dismissed them as inadequate nourishment. As a consequence they said that regrettably only the teeth condition of young macaques could be examined.
As a by-product of their study Stone and Henderson could distinguish differences in the behaviour of the troops in contact with tourists and those living out of touch: The isolated monkeys in Middle Hill were both harder to approach and had a lower acceptance rate of the pledgelets. They were more suspicious of humans than the monkeys in Ape's Den, who according to Stone and Henderson are approached by more than 1,000 tourists per day: The tourists "look to entice the macaques with food in order to get that perfect photo moment. However, this non-provisioned food tends to be of a more cariogenic nature, counting for 51.7% of all food consumed at this site. Furthermore, their contact with large numbers of tourists was causing the integrity of the macaques' social groups to break down, as they began to become dependent on humans. This induced them to foray into the town, resulting in damages to personal property such as buildings, clothing and vehicles. For this reason, feeding the macaques in Gibraltar is an offence punishable by law. Anyone caught feeding the monkeys will incur a penalty fine of up to 500 Pound Sterling. However, it is a known fact that since this law was introduced in the early 1930's, only one individual has ever been charged with this crime. To this day, we still see tourists feeding the monkeys and them venturing into the town area to raid the bins for additional food."
As an another line of research Stone and Henderson thus recommend to further examine behavioural differences between the two troops "by noting the time it takes for a macaque to accept a pledgelet from offering to taking. This would enable a greater understanding of habituation of primates and their confidence in interacting directly with humans."
We congratulate Stone and Henderson on their remarkable thesis and hope that more research about this subject will follow. If you wish to find out more about their study, contact us and we will forward your details to the researchers.