Rangers in the Democratic Republic of Congo's Virunga park have a new weapon in their fight against poachers. National Park authorities have trained five bloodhound dogs to track elephant poachers after a spate of incidents. The first investigation using the dogs was carried out last week and led to the discovery of illegal weapons. Poaching is one of the key threats to the animals in Virunga, a Unesco World Heritage Site in the war-torn eastern region of DR Congo. The park is also home to gorillas, chimpanzees, okapi, forest elephants and buffalo, among other wildlife. Some 300 rangers protect the park from poachers, rebel groups and illegal miners. 'Effective weapon' Park authorities now hope the bloodhound programme, which was implemented with help from a specialised Swiss centre and volunteers from the German police, will help to protect the vulnerable elephant population from ivory poachers. The dogs and their handlers got the chance to put their training into action on 1 March, when rangers spotted a dead elephant with its tusks cut off on the edge of Virunga.

     The Great Barrier Reef off the Queensland coast is home to a wealth of marine life

A UN team has arrived in Australia to investigate possible damage to the Great Barrier Reef by the mining industry.

Here's a look at just a few of the world's most endangered species:

Greater Horseshoe Bat

Rhinolophus ferrumequinum

IUCN Status: least concern

Population trend: decreasing

There are eighteen species of bat in Britain and all of them are endangered. The greater horseshoe bat is one of the rarest. One reason for their decline is the destruction of suitable roosting sites, such as old buildings and hollow trees. Changing land use from woodland and small fields to large scale agriculture has also had an effect. They have also suffered from the use of insecticides (poisonous chemicals sprayed on to crops to kill harmful insects) which have deprived the bats of their insect food. Due to conservation efforts its population in the UK has stabilized at about 5000.

Siberian (Amur) Tiger Panthera tigris ssp. altaica IUCN status: Endangered Population trend: stable