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Monthly Archives: October 2010

Silent assassins!

The thing with sharing one’s enthusiasm about the natural world, is that those profound “Wow” moments are often all-too brief and lose something of their impact through interpretation. The mental picture and the associated story may well be vivid and compelling, but as we have all become so accustomed to the privileged insights of programmes such as BBC1’s Life, we need a bit more to really whet our appetite.

 

The great thing about digital photography is that is makes capturing those precious moments more convenient. Not easier, just a bit more expedient. I continue to receive images from local photographers and they stitch a tapestry of incredible natural wonder in my email inbox.

 

A recent stunner once again came from the lens of Peter Vernon, who captured this image of a helpless small white butterfly pupae being attacked by an ichneumon wasp. A moment such as this reveals a grizzly and utterly compelling aspect of natural history and such a vivid image helps bring it into sharp resolution.

The ovipositor can be seen injecting an egg into this butterfly pupa

Ichneumon wasps (pronounced ick-new-mun) are members of the largest insect group the Hymenoptera. Meaning “membrane-wing” the Hymenoptera include bees, wasps and ants and is a group I am very fond of. Ichneumon wasps are typified as parasites, and often possess a gruesome looking appendage which is often misconstrued as a “stinger”. The long, thin needle-like structure is in fact an ovipositor, which is how the female wasp injects her eggs into a host. The term host conjures up images of conviviality and hospitality, in this instance a parasite’s host is a lot less reciprocal in nature.

 

Parasitic wasps with the longest ovipositors use them for injecting an egg into a grub inside a rotting log and therefore have to be very long and very mobile to negotiate their way towards the host. How she knows there is a little white larvae within the rotting log in the first place, I’ll leave to another article!

 

Back to our photo. The shot shows the female injecting a pupa, what looks like a seventh leg there is actually the ovipositor being manoeuvred directly down, positing the ova, or indeed ovum. As it is very difficult to tell categorically which wasp this is caught in the act, it is similarly tricky to say with any degree of accuracy exactly what ecology is being enacted, is one big egg being laid, or a collection of smaller ones? Suffice to say that what happens next is anything but pleasant.

 

The egg or eggs will sit in the soupy gunk inside the pupa as it overwinters. This ingenious use of a host to get your eggs through the worst the British winter possibly hints towards the evolutionary origins of the behaviour? The caterpillar continues to metamorphose and when spring comes and it’s time to emerge, the wasp’s grub leaps into action. Firstly it consumes its fill of semi-butterfly, metamorphoses within the pupa and emerges by eating its way out.

 

If the butterfly was free of the parasite and continued with its development unchecked, the pupa would split along a line of weakness at the front of the case when the butterfly emerged; a parasitised pupa will look discoloured and have a more clumsy escape route; anything from a small hole in the shell, to the entire head end being chewed off!

 

So next spring, keep an eye out for empty or emptying butterfly pupae and perhaps you will be lucky enough to see the results of this fascinating natural history.

 

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Posted by on October 16, 2010 in Insects

 

A consideration couple

Ladies and Gentlemen, drumroll please, I give you Pandion haliaetus the Osprey. What a magnificent bird!

A stunning view from the Seaton Marshes bird hide

This beautiful photograph was taken just last week from the Seaton Marshes bird hide, and it has persuaded me to feature the species in this week’s column even though its a bit late to go out there and see one.

Osprey move through our patch twice a year on their mammoth migration. Wintering in tropical West Africa, and breeding in the North of the UK. Osprey tend to dash through in the spring and saunter past in the Autumn. Young fledglings and failed breeding birds will come through first, as early as late July but more normally August. The parent birds will then follow along on their own familiar route towards the end of August. For several years the Axe estuary has hosted an osprey for much of September, and this year was just such an occasion.

Osprey are huge birds of prey, dark on the back with a pale underside and striped face. Their long squareish wings are rather thin, and with a good view it is hard to confuse them with any other bird in Britain. However, a jolly good view of a wild bird is something of a myth, its seldom the case that the first glimpse you get is anything more than just that, a glimpse. No, more often a snatched silhouette or banking profile is all you can see, and it is often easy to misidentify a diving black-backed gull or even a fast moving buzzard at distance, with a majestic Osprey – as I have found to my embarrassment on a number of very public occasions!

The feet are the business end of an Osprey. They are fish specialists and capture their prey by diving into the water feet first. The big, heavy feet are furnished with very large, long talons which themselves are replete with barbs on the underside to assist in gripping slippery fish. A feet-first plunge will often see the bird totally submerged, and a vigorous shake as the Osprey flies off sheds this water in a boiling haze. If you are lucky enough to see one catch a fish you will notice that they always prefer to carry their meal head first to a favourite feeding perch. In the Axe, they seem to be particularly partial to our huge thick-lipped mullet that cruise so lazily at the water’s surface.

The migration journey is so massive, so unfathomably difficult, its very hard to comprehend just what these birds put themselves through. A fabulous project by Roy Dennis, in the Highlands of Scotland, has fitted Osprey with small GPS units, and the flight of several birds can be followed in real time on Google Earth. Now, normally I am something of a dispassionate naturalist, distasteful of any unnecessary humanisation of wildlife. However, by giving each chick a name and tracking it personally, I challenge any of you to not get emotionally embroiled in this stunning natural drama.

A couple of years ago two chicks from a nest site in the eastern highlands set off on migration. One made its way through central England and passed through the Axe Valley. I saw the young female Osprey in the afternoon and watched her trace on the GPS that evening.

What a thrill!

She eventually made it to The Gambia, safe and sound. Her brother was not so fortunate, bearing south west from Scotland he flew down the Irish Sea and out into the Atlantic, never in sight of land. Possibly confused, possibly disorientated, this young male’s trace stopped after an ominous period of circular meandering in the open ocean. For more information visit http://www.roydennis.org

 

A fortuitous pair

Two godwits, but don't look at the tail!

As well as the glorious Osprey image, Tom also sent though a brilliant comparison shot of two wading birds that are often confused, godwits. On our estuaries at the moment, we have two species of godwit, a medium large wader with a long straight bill. Black tailed godwits and bar tailed godwits.

Now, all too often people tend to rely on the names of the wader to complete the identification, waiting patiently for a glimpse of the rear end before committing themselves to a decision. But as this photo so elegantly shows, there is a deal of difference between the birds when seen side by side.

Bar tails are much shorter in the leg, and have a conspicuous upward bend in the beak. Their plumage is also a pale version of the speckled colouration of a curlew.

Black tails on the other hand are longer and slimmer, with a dead straight bill and a plain grey plumage colour. Keep an eye out for these features, and you will be able to clinch identification of a godwit with certainty, without the need for them to take off!

Of course, bear in mind you might be looking at a North American vagrant Hudsonian godwit, but I’ll save accidentals and rarities for another column.

 
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Posted by on October 16, 2010 in Birds

 

Rich rewards for vigilance

Sometimes there is occasion for me to look over the border, outside the beloved District, when something really significant occurs in the natural world about which I can pen an article. Last time it was an American man with a germinating pea plant in his bronchiole, this week we’re a lot closer to home and a far more exciting news story.

Red backed shrikes have bred in England for the first time since the early 1990s!

What’s more they bred at a secret location on Dartmoor, and so have ended a drought of over 30 years for these birds breeding in the County.

 

Red backed shrikes make a welcome return, image rspb

 

This news was released last week by the RSPB, which has been co-ordinating a 24 hour vigil on the nest site, in collaboration with the Dartmoor Study Group and Forrestry Commission to ensure that no human interference could hamper this momentous occurrence.

The bird

Red backed shrikes are a charasmatic little bird, slightly larger but slimmer than a house sparrow; a bird whose elegant plumage belies a gruesome behaviour that has earned the bird the moniker “butcher bird”. Even though this is a passerine, a perching bird like blue tits and thrushes, its sharply hooked beak is a clue to its preferred food – shrikes are rapacious carnivores!

Red backed shrikes will take all manner of animal species, from crickets and grasshoppers, small lizards and even small birds. When a large prey item has been successfully snagged by the shrike’s needle-like talons, it often impales the corpse on a thorn, or barb and feeds on it at its leisure. Its this behaviour of hanging meat up to dry which led to the nickname.

A pale grey head, with a cops ‘n’ robbers black mask, gives way to a pale cheek and belly and a rich rufous back which gives this species of shrike its name of red back.

The history

50 years ago it was a fairly frequent breeder throughout the UK, but over that period numbers have dropped catastrophically, a decline exasperated by the illegal collection of the bird’s eggs, until by the early nineties none were breeding in England and only tiny breeding numbers at individual sites were recorded in Scotland and Wales.

Until this year it has only been recorded as a migrating bird in England, with singles turning up at migration hot spots along the South and East coasts most years, en-route between Northern European breeding sites and the winter destination of tropical Africa.

The significance

It was known that numbers were on the decline in France too, however Normandy populations were bucking this trend and doing very well. So conservationists were living in hope of the bird making a return one day.

Birders in the know in Devon had been keeping tabs on a few male birds seen in previous summers, however until this year none of these hopeful chaps had been joined by the all-important female. Then, in Spring 2010 a male on Dartmoor was seen with a female and the dream looked to be coming true.

Amazingly, or perhaps sickeningly, people who did not have the bird’s best interests at heart found out about the location of this population and so a round-the-clock vigil was put in place to ensure the brood’s safety from these maliciously selfish individuals. Egg collectors.

Its something which makes my blood boil. I hate the secrecy with which bird conservationists are forced to operate around some key species. Its my job to eulogise about Devon’s wildlife and its a terrible shame to only be able to bring you this news when the three chicks and both parent birds are far across the Channel on their way to West Africa. However, if that is what it takes to ensure the brood’s safety, then so be it.

With any luck, one successful breeding year will lead to another. Perhaps one or two of the chicks will also return to their birth County and attempt to expand the population, who knows? There are still a million and one disasters which could befall any of them before they reach an age to breed, both natural and man-made. However lets be optimistic: a link in the local food chain that has been missing around here since before I was born is back, and I for one hope I get a chance to see it myself as a breeding bird in Devon sometime very soon!

For anyone who is keen to see a red backed shrike in Devon, keep an eye on www.wildlifeindevon.org.uk for information about migrant bird sightings over the coming months. At the time of writing a single bird is being seen at West Charlton Marsh in the South Hams, and a trip to attempt to spot this charming little chap is highly recommended. Its unlikely to be one of the Devon breeders, as they moved out some time ago, but it will give you an idea of what we are missing and what, hopefully, will be returning to a heath, woodland or common near you in the next few years?

 
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Posted by on October 12, 2010 in Birds