Peter and Martha’s Excellent Aldabra Adventure, Part IV: Tortoise Tickling

Yep, you read that right. In 1976 my parents flew halfway around the world, then survived passage on a rickety freighter to be marooned on a tiny coral atoll in the middle of the Indian Ocean in order to…tickle tortoises?

Y’know, I can’t possibly explain it better than Peter. So once again…it’s all yours, Dad.

17 December

This day was devoted to tickling tortoises.  Meg had called our attention to the fact that the huge tortoises (similar to those on the Galapagos Islands) would respond to the presence of a flightless rail approaching from behind by rising up on all fours.  A similar response would occur if one took a straw and gently tickled the inside of a hind leg.  There is a controversy here as to whether this is to be viewed as a sexual response, or whether it is akin to the behavior seen among cleaner fish and their hosts, or crocodiles and the birds that clean food particles from between their teeth. Ectoparasites on the skin of the leg have been noted, so this is not unreasonable.  However, it is also possible, that the response is purely defensive.

[Ohhhkayyy…]

In case you suspect I might be making this up: here’s my mom, tortoise-tickling.

Our plan was to determine whether both males and females respond similarly, reasoning that if this was a sexual response, only females would display it.  So, Martha spent several hours tickling hind legs of mature individuals.  The first problem was to approach them without causing alarm, which leads to their withdrawing within their carapace altogether.  A second was to avoid having fingers rasped by their sudden movement, the solution to which was a longer tickling stick.  Finally, we had to determine the animal’s sex.  Males have a larger and fatter tail, and a more concave lower shell, presumably to aid in balancing on the the female’s back.  But, these traits are relative and, among the smaller, younger animals, not pronounced.  Many of the animals had identification numbers engraved ventrally, with their sex, as determined by tortoise specialists, entered in a log, but most of the animals were too heavy for us to invert so their sex remained a mystery.  However, given the proportion that responded to her tickles, we surmise the behavior is not sex-dependent.

[Aha! Science!!]

Visualize this ancient coral as you read the next paragraph. Ouchie!

Moving across the coral is hazardous, though the old-timers do develop a remarkable facility, so with time we, too, have become more more daring and are able to move fairly rapidly across the uneven terrain.  Just how competent we have come may be gleaned from the fact that last night we caught several goats for ear-tagging, which is done by cornering the animals on coral ledges overhanging the ocean.  These ledges are several meters above the shark filled ocean, and are composed of razor-sharp coral, with narrow pinnacles separated by deep, foot-grabbing crevices.  This is done in the dark, of course.  We survived unscathed, and scored a total of a half dozen goats, marked and measured.

[Oh, right…goats! The real reason for their long journey was goat study. So, tune in next week when we actually get back to goats.]

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