Friday, 1 April 2011

Dartmoor's most elusive mammal...

Have you ever walked the blanket bogs of Dartmoor? They can seem like an empty, open, drear place with little wildlife and an apparently limitless expanse of Molinia – a Chameleon-like grass which changes in character from purple-tinted green in summer to winter white. You may have heard the bubbling trill of Skylarks, the 'sweet-sweet-sweet' calls and songs of Meadow Pipits and perhaps, in the loneliest and most remote areas, the dry trilling calls of Dunlin. Other than these hardy birds and a specialist invertebrate fauna, you could be forgiven for thinking the place was pretty empty. Not so: take time, walk quietly and spend some time looking carefully at those bog pools – some are the home of a very special mammal: the Dartmoor Pygmy Sperm Whale. Known scientifically as Microkogia devoniensis, this is not only the sole freshwater European cetacean, but is also the world’s smallest whale; and it is a shy endemic resident of open bog pools on the blanket mires of Dartmoor.

Dartmoor Pygmy Sperm Whale - a rare glimpse in summer in an exceptionally well-vegetated pool. The flat back with dorsal fin just out of the water is characteristic of logging behaviour like this. They are easily disturbed, though, and an unwary footfall will result in nothing more than an expanding ring of ripples on the surface. This animal may be a lone bull, perhaps an adolescent feeding in the rich waters until he is of sufficient size to be capable of competing for a mate.

The Dartmoor Pygmy Sperm Whale is a fraction of the size of its better-known relatives - which include the world’s largest animal (the Blue Whale, Balaenoptera musculus). Measuring a maximum of 16cm from nose to tail, this is a unique creature in many different ways.

Much remains to be discovered about the biology and ecology of these diminutive specialities of the Dartmoor uplands. They appear to spend much of their time feeding in amongst the fringes of the Sphagnum moss which grows into the pools, perhaps hunting small invertebrates or even freshly-hatched tadpoles. There has been speculation that they even burrow their way into the mats of Sphagnum, though there is as yet no evidence of such behaviour. Their whereabouts in winter are also a mystery, although there have been reports of sightings at the ice fringe in the hardest weather, suggesting they probably remain faithful to their summer haunts throughout the year. It seems likely that they are able to live off their fat reserves through the tough winter conditions.

The clearest image yet obtained of this elusive species: the characteristic humped back and stubby projecting dorsal fin of a whale about to make a deep dive to the submerged vegetation. This appears to be an exceptionally large bull; the cows are more frequently seen, and are significantly smaller.

Your best chance of seeing one of these remarkable beasts is to find a bog pool, sit quietly and scan the water’s surface for the telltale ‘blow’ the animals make when they come to the surface. Their diminutive size means they surface rapidly, and even in a light wind, the ripples on the water’s surface can be sufficient to hide them. They rarely lift any part of their body far clear of the water, although tail-slapping and fin-beating are not unknown during their spring courtship period. However, other typical cetacean behaviour such as breaching is as yet unknown in the species.

Keep a close eye on the water when you're out there...

No comments: