Terence Blacker: To the Lord Howe rat I take off my hat

If ever there were a place on earth which proves that natural conservation requires human ruthlessness, it is the small, apparently perfect Lord Howe Island, off the east coast of Australia.

Lord Howe, which is run by a board of local families working with the state government, offers the world a lesson in environmental micro-management. Since the island was declared a World Heritage Site in 1982, the number of visitors permitted at any one time is 400. More controversially, the resident population is also controlled. The same hard line is applied to animals. Feral cats, pigs and goats have been culled for environmental reasons, and islanders are banned from owning them.

An altogether more formidable enemy is the black rat, which has been on the island since swimming ashore from a stricken ship in 1918. Rats are held responsible for the extinction of several bird species and are said to be an increasing threat to those that survive.

When I visited Lord Howe Island at the end of 2008, there was talk of a great poison assault on the rat population. The plan, brutally radical, has now been submitted and, if accepted by local and national government, will be put into effect in 2012.

This is the latest battle in an age-old war. Just over a century ago, the French bacteriologist Léon Calmette wrote a paper entitled "Declarons la guerre aux rats" and, since then, the human obsession with rats and their effect on the environment and health has become almost pathological. Mankind may have won a few skirmishes, but there is little doubt which species is winning the war.

The black rats of Lord Howe Island will survive the poison-bomb campaign. There is a large population there, and the island is hilly and wooded with plenty of alternative food sources. Large-scale campaigns of environmental intervention tend to prove that nature resists human manipulation invariably responding in a way which is unpredictable and unwelcome. Even modest attempts to tip the environmental scales are likely to go wrong. The first assault on the Lord Howe Island rats involved importing hooded owls from Tasmania. The owls quickly developed a taste for seabirds. Cats, when introduced, also preferred to snack on young birds.

It is arrogant to believe that mankind can, with an airborne toxic assault on a rare, fragile eco-system, control the way an environment develops. Shock-and-awe rarely works in the natural world, particularly when the enemy is that superb survivor, the rat.

terblacker@aol.com