Trip reports

Indoor Meeting - The history and natural history of Ascension Island

Friday, 12 October 2012

Ascension Island is over 1,000 miles from the African coast and over 1,200 miles from the South America. The island is volcanic and has a stark beauty. Although it was discovered in 1501 no country claimed it until 1819. The British garrisoned it as they were worried the French might use it as a base to free Napoleon from St. Helena. The island came to prominence in the Falklands war when it was used as a base for Vulcan bombers.
The land birds have been mostly introduced and include the waxbill, common myna, canary, red-necked francolin and house sparrow. The Ascension rail was endemic to the island but is now unfortunately extinct.
Green turtles lay eggs on the beach and there may be 5,000 females. After breeding they go west to the coast of Brazil returning every three years. Experiments have been carried out into how they navigate across the ocean. The turtles are tracked using satellites. There is some evidence that they may detect the smell of the island. One experiment that involved attaching magnets to the turtles seemed to suggest that turtles did not use magnetic field to navigate. However, another experiment that used turtles in a tank and manipulated the magnetic field was carried out. This suggested that magnetic fields did have an impact.
The Ascension Island frigate bird is an endemic species. Frigate birds have the lowest wing load of any bird; this is worked out by comparing the weight of the bird to the size of its wings. This allows it to cover vast distance in search of food. They have the longest care of young with it taking six months to fledge and another four to six months at sea. They have the longest life expectancy for a wild bird of thirty years.
The island contains a wide range of seabirds. Due to predation from introduced rats and cats most species were confined to breeding on rocks and islet surrounding Ascension. In the last ten years a feral cat eradication project has taken place and all domestic cats must be neutered. This has been a success, by November 2005, 726 pairs of five species returned to breed on the mainland. These were brown boobies, masked boobies, brown and white capped noddies, and the red-billed tropic bird. With the cats under control rat numbers are now increasing so money will be needed to conduct an eradication programme.

Huw Moody-Jones