Friday, March 26, 2010

Scene of the crime.

Pseudo-skink, attacked by night-heron.

Yellow-crowned night-herons were intentionally introduced to Bermuda in the 1970s. They were meant to be an ecological replacement for a closely-related species that became extinct some time after human arrival in the 1600s. That bird preyed upon the multitudinous land crabs, which, released from the pressure of at least one predator, eventually became a pest on golf courses, etc. (they burrow).

The yellow-crowns were taken from a population in Florida known to prey on crustaceans. It was hoped that they would, in addition to replacing a lost element of Bermuda's fauna, help with the land crab problem.

Young birds were hand-raised on the nature preserve, Nonsuch Island, and over the years many breeding pairs established nests there. They ate land crabs, as intended, but like other herons also showed more catholic tastes.

Uh-oh. Nonsuch Island is one of the last strongholds of the highly endangered Bermuda Rock Lizard ( a skink, genus Plestiodon), Bermuda’s only extant terrestrial endemic species. As the heron colony grew and thrived, the skink population declined. This was in part due to predation on young skinks by introduced Kiskadee Flycatchers and Jamaican Anoles, but there was suspicion that the herons might also have been preying on skinks.

Jamaican Anole, Anolis grahami, introduced to Bermuda in 1905.
In the 1990s, when I was on the island studying the skinks, I made a quick & dirty experiment with lumps of skink-coloured plasticine. I made faux-skinks and placed them on a beach where the herons foraged.

The first picture shows a typical result. Not shown are the heron tracks that surrounded the scene of the crime. The heron bit the faux-skink behind the head, and also at the base of the tail. There thus was evidence that herons were willing to explore skink-shaped models, perhaps identifying the shape as a known food. Eventually another biologist caught a heron red-handed, er, -billed. He saw it catch and eat a skink.

Restoring an ecosystem is a lot more difficult than messing one up.


Carol said...

We do have a way of mixing things up! Too bad! Lovely bird and lizard though. ;>)

PSYL said...

Very interesting post. Can't believe there's an island called Nonsuch Island!

Humans mess things up more often than clean them. Just the ways of creatures with an over-sized brain.

Anonymous said...

Cute anole, -love the red tail! :-)