Monday, 11 April 2011

Ravens hmm

"Ravens are one of the decade's real success stories. Once reduced to around a thousand pairs due to persecution, they have spread right back across Britain. In the last fifteen years numbers have increased by a whopping 134%. There are now over 12,000 breeding pairs.

I've been fascinated by these birds ever since I worked with them at the Tower of London and subsequently met my wife because of them (she was the Tower press officer at the time). So, I'm delighted by the species' recovery after centuries of persecution that saw them banished to our countries most remote and wild locations.

I've made a short film for tonight's Springwatch about one very special pair that have nested on the White Cliffs of Dover in Kent, the first birds to breed in the county for over 120 years. Their arrival is symbolic of the fact that, as a species, they've pretty much done it.

You can watch the film here:
Broadcasted on BBC June 2010.

Until recently they were imprisoned in the mountains of the Wales and Scotland. The White Cliffs are about as far south and east as they can reach from these north western hideouts. There were some initial suggestions that this special pair arrived from over the English Channel from France just 22 miles away. But they don't have ravens in that part of France, so it can't be a French invasion, these must be British birds.

Common Ravens are widely distributed and are not currently in danger of extinction. In some parts of their range, there have been localised declines due to habitat loss and direct persecution. Compared to many smaller Corvus species (such as American Crow), ravens prefer undisturbed montane or forest habitat or rural areas over urban areas. In other areas, their numbers have increased dramatically and they have become agricultural pests. Common Ravens can cause damage to crops, such as nuts and grain, or can harm livestock, particularly by killing young goat kids, lambs and calves. Ravens generally attack the faces of young livestock, but the more common Raven behavior of scavenging may be misidentified as predation by ranchers.

In the western Mojave desert, human settlement and land development have led to an estimated 16-fold increase in the Common Raven population over 25 years. Towns, landfills, sewage treatment plants and artificial ponds create sources of food and water for scavenging birds. Ravens also find nesting sites in utility poles and ornamental trees, and are attracted to roadkill on highways. The explosion in the Common Raven population in the Mojave has raised concerns for the desert tortoise, a threatened species. Common Ravens prey upon juvenile tortoises, which have soft shells and are slow-moving. Plans to control the population have included shooting and trapping birds, as well as contacting landfill operators to ask that they reduce the amount of exposed garbage. A hunting bounty as a method of control was historically used in Finland from the mid-18th century until 1923. Culling has taken place to a limited extent in Alaska, where the population increase in Common Ravens is threatening the vulnerable Steller's Eider (Polysticta stelleri).

Ravens can mimic sounds from their environment, including human speech. They have a wide range of vocalizations, which remain an object of interest to ornithologists. Gwinner carried out important studies in the early 1960s, recording and photographing his findings in great detail.

Fifteen to 30 categories of vocalization have been recorded for this species, most of which are used for social interaction. Calls recorded include alarm calls, chase calls, and flight calls. Non-vocal sounds produced by the Common Raven include wing whistles and bill snapping. Clapping or clicking has been observed more often in females than in males. If a member of a pair is lost, its mate reproduces the calls of its lost partner to encourage its return.

The brains of Common Ravens count among the largest of any bird species. Specifically, their hyperpallium is large (see avian pallium). For a bird, they display ability in problem solving, as well as other cognitive processes such as imitation and insight.

Are ravens a problem?Questions are now being asked about large numbers of ravens becoming a problem. There are reports of gangs of juvenile ravens numbering in their hundreds swooping across moorland and decimating wader nests, taking eggs and chicks alike. Just as with the return of so many top of the food chain predators, like otters and pine martens, is the return of the raven going to cause its own dilemmas for the conservation world?

Ravens are astonishing birds, with over 50 different vocalisations, intelligence that rivals primates and a role in our history and folklore that few other species can match.

How to identify a raven
There are eight distinctive members of the corvid family in Britain: the raven, carrion crow, hooded crow, jackdaw, rook, jay, magpie and chough.
Of these birds, five are black and it can be confusing telling them apart, especially from a distance.

•Choughs are the easiest to identify as they have a bright red bill and legs.
•Jackdaws are small, with a faintly silvery head and piercing grey blue eye.
•Rooks have a distinctive white mantle at the top of their bill.
Distinguishing carrion crow and raven is where it starts to get a little harder. I find the easiest method to separate the two is to listen to their call. The raven has a very distinctive "cronking" call (have a listen here) that couldn't be mistaken for any other bird. If the birds aren't calling then look for the very wedge-shaped tail in flight of the raven, crows don't have it.

Finally, there is size. Ravens are much, much bigger birds than crows and if you can see the two together you'll notice it immediately. Ravens actually have a bigger wingspan than a buzzard... that's how big they are.

Close-up, the raven's most distinctive feature is its bill. Needed it to pull apart raw flesh, it's a vital tool for a bird which scavenges on dead animals.

Across its range in the northern hemisphere, and throughout human history, the Common Raven has been a powerful symbol and a popular subject of mythology and folklore.

In many post-conversion Western traditions, ravens have long been considered to be birds of ill omen, in part because of the negative symbolism of their all-black plumage and eating of carrion. In Sweden, ravens are known as the ghosts of murdered people, and in Germany as the souls of the damned. In Danish folklore, valravne that ate a king's heart gained human knowledge, could perform great malicious acts, could lead people astray, had superhuman powers, and were "terrible animals".

As in traditional mythology and folklore, the Common Raven features frequently in more modern writings such as the works of William Shakespeare, and, perhaps most famously, in the poem "The Raven" by Edgar Allan Poe. Ravens have appeared in the works of Charles Dickens, J. R. R. Tolkien, Stephen King,and Joan Aiken among others.

It continues to be used as a symbol in areas where it once had mythological status: as the National Bird of Bhutan, Official Bird of the Yukon territory, and on the Coat of Arms of the Isle of Man (once a Viking colony).

If you're still stuck the RSPB have a really good online bird identifying tool."

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