The Barbary Apes of Gibraltar

For many years zoologists and others have commented on the mystery of Gibraltar’s Barbary Apes – the fact that members of the ape colony on the Rock appear and disappear unexpectedly, sometimes showing up in the company of new apes never seen before – despite the fact that there are no known hiding places on this landmark site.
The speculation is that an age-old subterranean tunnel exists, beneath the Straits, connecting Gibraltar with the North African coast, and that the apes have been using this tunnel for transit since time immemorial.
Author-iconoclast Charles Hoy Fort, a well-known collector of reports on strange phenomena, wrote about this theory in his book Lo! (1931):

...In the London Daily Mail, July 1, 1920, a correspondent expresses an idea... as to mysterious appearances and disappearances of the Barbary apes of Gibraltar, conceiving of a submarine tunnel from Gibraltar to Africa. “All these creatures were well-known to the staff of the signal station on the Rock, many of the apes being named. The numbers sometimes change in the most unaccountable way. Well-known monkeys are absent for months, and then reappear with new, strange, adult monkeys of a similar breed. Those who know Gibraltar will agree that there is not a square yard on the Rock where they could have hidden.”

A few pages later in the same book, Fort cites another press report on the same topic:

In the New York Sun, Feb. 6, 1929, Dr. Raymond L. Ditmars tells of an “old legend” of a tunnel, by which apes travel back and forth, between Africa and Spain. No special instances, or alleged instances, are told of. In Gilbard's History of Gibraltar, published in 1881, is mention of the “wild and impossible theory of communication, under sea, between Gibraltar and the Barbary coast.” Here it is said that the apes were kept track of, so that additions to families were announced in the Signal Station newspaper. The notion of apes in any way passing across the Mediterranean is ridiculous to Gilbard, but he notes that there are so many apes upon the mountain on the African side of the Strait of Gibraltar that it is known as the hill of Apes.

Although commonly referred to as “Barbary Apes,” these primates are actually Barbary Macaques, part of a species of true monkeys (Macaca sylvanus), not apes. Apart from man, they are the only primates that live freely in Europe.

The Gibraltar macaques are in fact descended from North African – Moroccan and Algerian – populations of Barbary macaques that today can be found mostly in the Middle Atlas mountains. The macaques have been known on Gibraltar since the British first captured the Rock in 1704. DNA studies have shown that in addition to their Moroccan and Algerian origins, the Barbary apes of Gibraltar have a third DNA source, probably from an extinct Iberian population.
According to conventional wisdom, the Gibraltar apes were imported by the Arabs and Berbers who conquered Spain and ruled substantial parts of the Iberian Peninsula from 711 to 1492. The macaques were said to have been kept as pets by the wealthy.
The belief in a subterranean passage under the Straits of Gibraltar survives to this day. A Gibraltar tourism website discusses St. Michael’s Cave, a geological structure linked to the legend of the tunnel:

St Michaels Cave has interested visitors to Gibraltar ever since the days of the Romans. The cave was long believed to be bottomless. This probably gave birth to the story that the Rock of Gibraltar was linked to the Continent of Africa by a subterranean passage over 24 km long under the straits of Gibraltar.
Pomponious Mela, one of the earliest writers on geography who lived about the beginning of the Christian era named the cave after a similar cave in his home city in Italy.
It was at one time believed that when the Spaniards first tried to retake Gibraltar from Britain in 1704, a party of 500 of their troops spent a night in the cave after climbing the East face of the Rock. Next morning, however the alarm was given and troops of the garrison surprised and overpowered the raiding party. Many other small caves are linked to the main chamber.

In 2001, a Canadian traveler, James Smith, posted some interesting observations on the Gibraltar Barbary Apes on the Epinions website:

One of the most well known attractions of Gibraltar, second only to the famous rock itself, are the bands of semi wild apes that live there. The Barbary Apes of Gibraltar are the only wild primates in all of Europe. There are approximately 200 apes in several extended families or packs scattered among the higher reaches of the "rock" mainly near the Upper Siege tunnels and at the "Apes Den" near the cable car station. The later is a regular stop on all the tours.

Candy stealing aside, the apes are used to humans and tolerate the daily procession of tourists who come and watch them play. They will allow you to get close and feed them and even pose for pictures. Some of the older ones will even ham it up for the cameras as long as you treat them. Although they are wild animals, there are only two things to be careful of, as the tour guides point out.
First never try to get too close to the baby apes. Like most animals, the mothers are very protective. Secondly, as in the case of the candy lady, be careful of anything in your hands especially food and/or shiny objects. As far as the apes are concerned anything they can grab they will, and they'll keep it. Somewhere in the crevices on the side of the rock it is rumoured there is a cache of sunglasses, jewelry, cameras, and other items that used to belong to tourists who didn't heed their guides warnings.
No one is quite sure of how the apes came to Gibraltar in the first place. One theory is that they arrived with the British soldiers and sailors as pets. There is however no records to support this idea.
Another theory is that they may have migrated from Africa perhaps through a subterranean tunnel under the Mediterranean Sea. This theory may not be as far fetched as it seems. It is only fifteen miles across the straight to Morocco and the only other known colonies of Barbary Apes are found in the Middle Atlas Mountains of that country and neighboring Algeria.
Not only does no one seem to know where the apes come from, but no one is quite sure where they go when they die. No one has ever found the remains of any of the colony's deceased apes. It appears that they seem to know when it is their time and disappear into the wilds of the mountain to some undiscovered ape graveyard.

Needless to say, the existence of a subterranean tunnel beneath the Straits of Gibraltar has never been confirmed. The mystery of the Barbary apes of Gibraltar remains unsolved.