Saturday, 27 June 2009

Finding Field Voles

Under the square of roofing felt, I found a pair of tiny, baby voles. I watched them and worried for their safety, as they stumbled blindly around. They had fur, so they must have been at least 9-10 days old, but their eyes were squeezed shut and they looked incredibly vulnerable. Not wanting to disturb them too much, I took a quick photo and gently replaced the roof of their home.

The rough grassland that they were living in suggested that they were baby field voles, as opposed to bank voles, which look very similar, but prefer more wooded habitats. I wanted to be sure though, so I searched for more clues. I followed one of the well-trodden vole runs through the grass and discovered a feeding station - a pile of neatly cut grass and plantain, nibbled at the ends to form a distinctive 45 degree angle. Next to this was a latrine of fresh, green-brown droppings. All of these signs indicated that the babies were field voles.

The next day, I was eager to see how the little voles were growing and I hurried back to the tile. I peeled back the felt very slowly and gently, but my heart dropped at the sight of one of the baby voles, lying still and lifeless on the bare ground. The other one was nowhere to be seen. Sadly, I laid the tile down again, wondering how the youngsters had died. Did they fall victim to a predator – maybe even a shrew? Or had their mother died, before they were fully weaned and able to fend for themselves? I would never know.

A field vole’s life is fraught with danger and is always short. It has many different predators, including kestrels, owls, foxes and stoats, which all kill huge numbers of voles. However, field voles breed prolifically; the young females are able to mate at 6 weeks old and between March and December, a female may have 4-5 litters, each containing 2-7 young. So, despite being apparently helpless in the face of so much adversity, it is a highly successful species and at a count of about 75 million, it is the only mammal species in Britain to outnumber humans.

Now you do it
Field voles are common and their signs are easy to find, once you know what you are looking for. Search at the base of grass tussocks, or under pieces of corrugated iron for their nests - balls of grass, very loosely woven together. You may also find their feeding stations, which are piles of grass and other plants, cut into similar sized lengths with the ends usually having an angle of 45 degrees. It used to be thought that different vole species cut vegetation at specific lengths, but there is so much overlap between the species, that this is not a reliable method of identification. A more reliable method of identification is by their latrines; field vole latrines contain oval, greenish droppings of approximately 5mm in length and 2-3mm in diameter. Bank vole droppings are blacker and water vole droppings are larger (8-12mm in length and 4-5mm diameter). See the ARKive website for more information on field voles and some fantastic videos.

If you live in Sussex, why not take part in the Sussex Mammal Group’s field vole survey? See the Sussex Biodiversity Records Centre website for more information.

Live trapping, using Longworth traps, is also a good way of getting closer to field voles, but make sure that you know what you are doing first. The Mammal Society has a Longworth trap loaning scheme and runs courses on small mammal survey techniques. If you do carry out trapping, be aware that you are likely to catch shrews and will therefore need a shrew license from the relevant Statutory body (e.g. Natural England).

Tuesday, 16 June 2009

Ghostly Goatsuckers

It was once a widely held belief that nightjars sucked milk from the teats of domestic goats. A nasty cattle infection, caused by the warble fly, was also attributed to nightjars, which were thought to attack young calves with their beaks and infect them. As a mysterious bird of the night, equipped with a haunting song, nightjars were often considered with suspicion and bestowed with a host of colloquial names, including goatsucker, scissor-grinder and churr owl. It is these intriguing creatures, so surrounded by folklore, that I set out to find.

It was early evening when I arrived at Aylesbeare Common in East Devon, a known stronghold for this summer visitor, and I strolled around the reserve through a mosaic of dry and wet pebblebed heath, woodland, ponds and grassland. The only sound was the clack of stonechats, singing from the tops of gorse bushes. As the sky darkened and the moon rose, the pale orchids and sheets of cottongrass began to glow and I watched bats circling below planes stacked at Exeter airport. A tawny owl flapped slow and low over the heather.

Then, everything was still for a long time. As the air chilled and I started to wonder whether I should try my luck in a different part of the reserve, or perhaps just give up and go home, I heard a faint churring sound. I turned my head, struggling to identify where the sound had come from and scanning the bushes for some movement that might give the bird's location away. But there were no other clues, so I started to walk aimlessly, deeper into the darkness. Suddenly, a bird with white indicator patches on its wings swooped in front of me and landed on the branch of a dead tree. I stopped in my tracks. A nightjar. The white wing bars and tail spots gave its sex away – it was a male. From its prominent perch it began its moody percussion song, an exotic sound that seemed far more suited to its winter home in Sub-Saharan Africa than southern England. I listened, entranced, to the low, two-tone trill, which reverberated around the heath. Then, out of nowhere, another male nightjar appeared and chased the original bird from its place. With a loud clapping sound, the pair flew off, taking their territorial dispute out of sight.

As I walked back towards my car, I stumbled across another nightjar, which was churring from a tree. The bird’s song was periodically interrupted by noisy, wing-clapping circuits as the bird hawked for moths, slapping its wings together above its body. The nightjar's mouth is adapted to catching insects on the wing, with jaws that can move from side to side, as well as up and down and fringing bristles, which are probably used in food detection and are regularly groomed by the nightjar, using its serrated middle toe. It also has a highly sensitive palate, which means that its jaws snap shut at the slightest touch, rather like a Venus Fly-trap. But, it is the nightjar's large eyes, complete with a tapetum and special cells that are thought to increase the nightjar’s ability to see contrast, which allow it to hunt by night.

Unfortunately, my eyesight was not a patch on the nightjar’s and soon I was unable to make out the bird in the gloom. I tore myself away, knowing that, just like the nightjars, I would definitely be back next year.

Now you do it
Nightjars start to arrive in Britain in April and begin to leave in mid-July, so you still have time to see them this year. Your best bet is to head to an area of heathland or moorland in southern Britain, either just before dawn or at dusk. Choose a nice warm day, as Nightjars are less active in cool, wet weather.

For a list of places to see Nightjar, check out The Forestry Commission website and if you would like to hear the wonderfully unique churr of a Nightjar, visit the RSPB website.

Conservation Status
The nightjar is listed on the RSPB Red List, which means that the species is of high conservation concern and it is a UK BAP Priority Species. The number and range of Nightjar has been declining for much of this century and reasons for the decline include reduction in the amount of suitable habitat (e.g. heathland), disturbance (e.g. recreational activities which can lead to disturbance of nesting and roosting nightjar) and the use of pesticides, which reduces the amount of insect prey available. Climate change may also be playing a part in its decline. The Nightjar is afforded legal protection under Schedule 1 of the Wildlife and Countryside Act 1981, which (amongst other things) makes it illegal to disturb a Nightjar or its young at a nest, or whilst it is nest building.