Sunday, April 27, 2008

Death from above, 5% alc/vol.

The Bermuda Rock Lizard or skink, Plestiodon ( formerly Eumeces) longirostris has a remarkable sense of smell, and is critically endangered. Many factors contribute to the latter fact, one being the former.

It is Bermuda’s only native lizard, and evolved on a landmass that at one time bore thousands of nesting seabirds, including Bermuda Petrels, known as Cahows, and White-tailed Tropicbirds, which nest within cavities in the layered aeolian sandstone that forms the islands. The skink is attracted to strong-smelling, including foul-smelling, organic material. Presumably this would have been advantageous in a place strewn with the nutritious by-products of rock-nesting sea-birds -- broken eggs, dead chicks, scraps of regurgitated fish or squid …. It wasn’t a tidy place.

Bermuda Skink habitat.

A picnic on a beach such as this can attract skinks, as the smell of tuna salad or peanut butter wafts cliff-ward. Little orange heads pop out, and the skinks plummet down to the beach below. (Head-long freefall is part of the locomotory play-book.)

Bermuda Skinks checking out peanut butter.

Skink unable to believe his good luck. A bounty of sardine.

I don’t know other lizards that are so easily drawn to odoriferous substances. I once gave a talk on this animal to a room of herpetologists who had, collectively, studied all over the planet. I asked if anyone knew of another species that was similarly olfactorily oriented. No one did. There is one herpetological advantage to the behaviour:
Bermuda Skink in pop bottle, again with sardines.

The attraction to the malodorous makes them easy to trap for population and other studies. But it also has cost this lizard dearly, in a relatively small place that has been inhabited by humans for four centuries. A discarded beer bottle can be a very smelly thing, and has an opening large enough for a skink to enter. Like a lobster trap, it’s easy to enter, but difficult to escape, and a skink can quickly succumb to heat stress, especially under the subtropical sun. What makes an attractively stinky beer bottle even more attractively stinky? A dead skink inside, ripening in the heat. I found long-ago discarded Amstel bottles filled with handfuls of disarticulated bones and the cast exoskeletons of the fly maggots that had cleaned away the flesh. I remember one bottle, retrieved from the dense forest above the beach in the second picture, contained twelve parietal bones, the central bone of the roof of the skull. One drunken toss from a boater, 12 dead skinks. Not much wonder the species is critically endangered, when one of the last few decent habitats is a minefield of invisible deathtraps.

If you’ve been lucky enough to visit the island where I worked, you might know where this picture was taken. Judging by the shadows, it’s early, probably breakfast time. I wonder what we were eating that drew them. Something deliciously stinky.

Anyway, here are more pictures of these creatures. Sorry they’re not too sharp; they are scans of prints or slides.

Another post on this species here.

Yet another here.

More on Plestiodon (=Eumeces) longirostris and other challenges it faces are discussed in the following two manuscripts: here and here (both mss written in 1993).

1 comment:

Anonymous said...

shameful the way we toss garbage and the damage it does...