Friday, 30 April 2010

Little Grebes shy and retiring

Down the road at Livermere the Little Grebes are going about the business of breeding in their usual shy and retiring manner. Familiar to many readers as the dabchick, the Little Grebe is the smallest of our grebes and my own personal favourite waterbird. While the Little Grebe may lack the elaborate plumage ornamentation of the more familiar Great Crested Grebe, there is still something charming about its appearance. It might be the combination of small size and powder-puff rear end that promotes such an endearing character or it might be the sense of understatement, the ease with which the Little Grebe exploits its watery world without any fuss or drama.

Just as they lack the flamboyant headdress of their larger relative, so Little Grebes also refrain from the associated elaborate courtship displays so often shown on wildlife documentaries. Instead, Little Grebes use their trilling calls, with the individual birds duetting to one another at close range and in a highly ritualised fashion. Sometimes a bird will go a stage further and present some waterweed to a prospective mate, a token of affection or a demonstration of their ability to provide for the pair’s future needs? Of course, it is the latter, with the display often progressing to a more purposeful piling up of weeds, the very basics of nest building.

Like other grebes, the Little Grebe constructs a simple nest in shallow water out of fresh and decaying aquatic plants. This mound of vegetation clears the water’s surface and allows the grebe to shape a simple depression into which the eggs will be laid. Positioning the nest in the water like this reduces its accessibility to terrestrial predators but does not necessarily spare it from more versatile ones, like Grey Heron or Mink, and there is also the danger of a sudden rise in water level. The nest site is usually on some small waterbody or on the still reaches of a lowland river, the nest itself placed among emergent vegetation or, as is the case at Livermere, within the branches of a tree that has toppled into the water.

The adult birds are very careful when visiting the nest, approaching quietly so as to avoid attracting unwanted attention to their nesting attempt. The young leave the nest and accompany the adult from a very young age and may sometimes be carried on the parent’s back, although this behaviour is less common than is the case for the Great Crested Grebe. In some ways it is the challenge of picking out the Little Grebe’s nest that attracts me to this bird. You have to work at finding the nest to prove that they are breeding at the site.

Thursday, 29 April 2010

Sparrowhawks display overhead

Our local Sparrowhawks have been much in evidence over the last few days, soaring above the garden with an almost lazy ease. This suggests that these birds are breeding locally, a sure sign of their recovery from the effects of persecution and pesticide residues that saw their loss from much of the east of England just a few decades ago. The return of the Sparrowhawk has not been welcomed by everyone, with letters to the EDP over the years testament to the range of emotions stirred by the return of this native hunter. However, its recovery suggests that we have managed to fix some things in the wider environment and improve the fortunes of previously scarce species.

The presence of this pair of Sparrowhawks above the town unsettles the local doves but the hawks are probably more interested in displaying their ownership of this particular territory than in anything else. You can tell that the two birds are a pair because the female is noticeably larger than her mate, a pattern present in a good number of raptor species and something known as ‘reversed sexual size dimorphism’. It is thought that the size difference stems from the different roles of the two sexes. The male is the hunter and main food provider while the female’s is incubating eggs or brooding young; he needs to be agile enough to catch prey and being small and light allows this. The female has to have sufficient body reserves to cope with the energetics of reproduction so she cannot be as light and, therefore, as agile. The difference in size also allows the hawks to feed on differently-sized prey, the male taking small birds, up to the size of a Blackbird, and the female taking larger prey, up to the size of a Woodpigeon. By preying on slightly different prey the two birds reduce the amount of competition between them. Reversed sexual size dimorphism is more pronounced in raptors that pursue difficult to catch prey (like birds) than it is in those species that take more slowly moving prey (like small mammals) or which scavenge.

Food availability has a tremendous influence on Sparrowhawk breeding success. Males can only successfully attract and retain a female if they can prove that they are a good hunter. The male feeds the female at the future nest site and she will only hang around if she is well-provisioned. If not, she’ll leave to find a better male. Once the birds are paired, then food supply becomes all important for the resulting chicks and breeding success will be determined by how much food the parents can ultimately provide. The presence of Sparrowhawks here suggests a healthy population of their prey.

Wednesday, 28 April 2010

First 'proper' spring butterfly on the wing

Like me, you have probably seen a few butterflies on the wing over recent weeks. These may well have included Peacock, Small Tortoiseshell, Comma and Brimstone, all of which overwinter as adults. Just possibly, you may have encountered a Red Admiral, a species which has recently demonstrated its ability to overwinter here as an adult, but which is likely to have struggled this particular year because of the severity of the weather.

Orange Tip, by MIke Toms

Our other butterflies overwinter at different stages of their life-cycle, with some spending the winter as caterpillars, others as eggs and some as pupae in a chrysalis. The Orange-tip is one of the species to spend the winter as a pupa, overwintering in tall vegetation somewhere close to the foodplants upon which it will have fed as a caterpillar; these include Cuckoo flower (Cardamine pratensis) and Garlic Mustard (Alliaria petiolata). Other foodplants are sometimes used, including garden favourites like Honesty (Lunaria annua) and Dame’s Violet (Hesperis matronalis), although the survival of the caterpillars on these plants is thought to be poor. One of the most striking things about the Orange-tip life-cycle is that although most adults emerge from pupae come spring, some are thought to delay their emergence by one or even two years. While this unusual behaviour has been recorded in captive-reared stock it has not yet, as far as I am aware, been demonstrated in the wild. One could imagine how the ability to delay emergence might be a useful survival strategy if faced by unfavourable springtime conditions.

While I am always keen to record my first Peacock or Comma of the year, I tend not to think of them as this year’s butterflies because they will have been on the wing since last autumn, visiting late season food sources to lay down the fat reserves needed to get them through the winter. This is why it is the sight of the first Orange-tip of the year that really gives me a buzz, a butterfly signal that spring is well and truly with us.

Many readers will only be aware of the male Orange-tip butterfly and will have never knowingly seen a female. This is because it is only the male that sports the orange, fingerprint smudges of colour on the wing tips that are so characteristic. Females are more subdued in their appearance and resemble our other whites, though the strongly patterned underside of the hind wing, with its grey-green splodges, is a very useful feature to look out for. Large Whites and Small Whites are also on the wing from April, so do take a closer look at any ‘small’ whites that you see in case they turn out to be a female Orange-tip.

Tuesday, 27 April 2010

A special treat

The other weekend I was treated to a very special sight. I’d been lucky enough to go out into the forest with a couple of nest recorders, specially trained and licensed individuals who monitor bird nests for the British Trust for Ornithology (BTO). Nest recording is an extremely important component of the BTO’s work, providing information on those changes in breeding success that might result in population decline or flag up the worrying effects of human activities. It was nest recording that highlighted the impact of organochlorine pesticides on the breeding success of birds of prey like Sparrowhawk and Peregrine.

As well as helping to locate nesting birds, I was taken to see two rather special nests, both of species whose nests I had never seen before. The two species were Siskin and Crossbill, both of which are very early nesters and their breeding attempts were now well advanced. There seem to be very good numbers of both species in the forest this year. Crossbill numbers in particular tend to rise and fall, with increased numbers breeding here in years when we have had a good influx of birds from Scandinavia during the previous winter. We were certainly treated to excellent views of both species as they fed, perched and called in the firs.

Although Crossbills are fairly ‘tame’ when nest building and appear to disregard the observer, they are rather furtive when they have eggs or young in the nest. Visits to the nest to feed are rather infrequent and the birds are very careful in their approach. The nest itself is also rather hard to spot, placed on a branch high in a conifer. We had to strain our necks to spot where the nest was located, the slight bulge of material silhouetted above the branch on which it was placed. The same was true for the Siskin nest which, though placed lower down in this instance, was rather more compact. We managed to get a good view of the Siskin nest from slightly below the horizontal, standing well back but using our telescope to good effect.

Conditions must be difficult for these birds, nesting so early in the season, and even though the day of our visit was a warm and sunny one, there were still the remnants of the gusty winds that had been present over previous days. One of the Crossbill nests that we went to check on had been blown down by the wind, a small amount of debris left in the tree, with nest and eggshell remains scattered across the forest floor. There was a good chance that the birds from this failed attempt would have another go so all was not lost for them.

Monday, 26 April 2010

Kites flying high

A recent trip to Oxford by car revealed just how well the English Red Kite population is now doing. Persecuted to extinction within the country by the end of the 19th Century, the species hung on only in Wales and the current population stems from a great deal of high profile conservation work.

For me, as a child with a growing interest in birds and birdwatching, the Red Kite remained a tantalising bird, wished for but never seen on holidays to Wales (we were in the wrong part of Wales). Even though most of the persecution that had previously harried the species had ended, the conditions in Wales were such that the population found it difficult to prosper or to recolonise former haunts. It was for this reason that a decision was taken to reintroduce the Red Kite to England and Scotland, using birds from elsewhere in Europe (Spanish birds for the English releases and Swedish and German birds for the Scottish ones). These began in 1989, with young birds released to a site in the Chilterns, operated under carefully supervised and controlled conditions. Over the next five years 93 young were released from this site and the offspring from these birds provide the backbone of the population that can now be found from Oxford south to Didcot and beyond. Such has been the success of the reintroduction that you cannot drive up the M40 in daylight hours without seeing a good number of kites on your journey. The other day we saw three dozen, with 11 birds in the same field of view at one point.

Other releases have followed, including one in Central England and one in Yorkshire. These populations are also doing well and the species is becoming an increasingly common sight across much of the country. I now see Red Kites fairly regularly in Norfolk and at least one bird has been haunting the same bit of the Brecks over recent weeks, perhaps an early indication that we will soon have them established here as a breeding species.

Nesting kites suffer from the unwelcome attentions of egg collectors and birds are sometimes also targeted by a minority of landowners who, incorrectly, assume them to be a threat to game or livestock interests. The kite is an opportunist, taking advantage of whatever source of food is available locally and is happy to scavenge scraps. In parts of Didcot the birds are attracted to bird tables where some householders provide meat scraps specifically for the kites. Now, there’s a bird that would make an impressive entrance at your garden feeding station. It’s certainly good to see them on the wing, a sign that our attitudes are changing for the good.

Saturday, 3 April 2010

The long journey north

It’s a long way to Inverness and, with the first glimpses of spring in the south, I wonder whether my journey will deliver me back to the last remnants of winter. There is something special about long distance train travel through open country and it always makes me re-evaluate the beauty of the British countryside. Trains take you to parts of the landscape removed from roads; they follow contours and cross wide floodplains. Of course, this is no substitute for actually being out there; immersed in the landscape with its smells and sounds, being buffeted by a chill wind or bathed in the warmth of the sun’s rays.

To my mind, travelling by train is very different from travelling by car. Whereas a train journey through open country is usually bordered by nothing more than a thin wire fence, that on a road is hemmed in by banks and barriers and you rarely get the chance to look at the landscape in any detail.

This particular journey is one of contrasts; from the open landscapes of the fens, with their endless fields of deep and dark peaty soil, it cuts north through England before finally reaching the towering mountains of the cairngorms, covered in the last remains of the winter’s snow. My favourite part of the journey is the last leg, a two-hour haul from Perth north to Inverness. Here the train passes through some of the most striking scenery to be found in Britain, a mixture of raging upcountry rivers, steep hillsides and high peaks. Patches of snow remain in the deeper gullies but the volume of water in the rivers underlines just how recently much of the snow has melted. Herds of Red Deer graze close to the railway, shuffling uneasily at the train but no doubt used to the steady stream of passing machinery.

One reason that I find train travel so engaging, in terms of the way in which it connects me to the landscape, is that these long journeys give you plenty of time to think. By watching the landscape you can shut out your fellow passengers and really take in the detail of what is scrolling by outside of the window. You can follow the lines of rivers, wonder at the contents of dark patches of woodland and seek out signs of the larger wildlife that lives in the landscape through which you are passing. And when the train passes through some of the more dramatic parts of the countryside you can question your place in the wider scale of things. While train travel enables you to look outward, car travel seals you into a bubble and shuts you off from the world around you.

Friday, 2 April 2010

Mistle Thrush well into breeding season

The local Mistle Thrushes have been singing for some time now. Indifferent to the wind and rain of last month, hence the local name of ‘storm cock’, their song has been heard on and off for many weeks. I suspect that they are now incubating a clutch of eggs or, possibly, feeding young chicks. Mistle Thrush nests are either placed up against the trunk of a tree, in the crook where branch meets trunk, or further out in a fork on a horizontal branch.

The nest itself, like those of certain other thrushes, has several distinct layers to its construction. An outer layer of loosely woven grasses and roots is held together by a layer of mud and rotten wood. Finally, the nest cup is lined with finer grasses and, occasionally, pine needles, the latter possibly serving as an insect repellent against nest parasites. In my opinion the nest is less tidy than those of Blackbird or Song Thrush and sometimes incorporates bits of paper or plastic.

Mistle Thrushes seem to do well in suburban areas, as does the Song Thrush, though both species have undergone significant declines in their populations since the 1970s. They are, however, often overlooked and many casual observers regard the two species as being just one – the thrush. While the Song Thrush (smaller than a Blackbird) is a bird of warm tones, the Mistle Thrush (larger than a Blackbird) tends to show colder tones, with pale greys and browns. One of the best features to use when separating the two species is the shape of the spots on the upper part of the breast. On Song Thrush these are shaped like upside-down arrowheads, though they become more rounded and slightly elongated on the flanks. In Mistle Thrush the spots are round in shape and they often coalesce to form darker patches on the flanks.

Later into the year you may well see family parties of Mistle Thrushes feeding together. These small groups of birds remain wary around humans and will often fly away at your approach, uttering an alarm call that sounds like an old football rattle. Perhaps surprisingly, given their wary nature, Mistle Thrushes can be rather noisy around the nest, giving its location away to human observers and potential predators alike. Mind you, the Mistle Thrush is a formidable bird and pairs will not hold back when attempting to drive potential predators away from the nest. You should also keep an eye out for adult Mistle Thrushes feeding on open areas of short turf and then carrying food back to hungry young. Although the young remain in the nest for just two weeks, the adults will undertake more breeding attempts throughout the summer.

Thursday, 1 April 2010

Diving beetles on the wing

Making my daily journey to and from work on foot means that I sometimes come across interesting insects and plants along my route. The other morning, for instance, I came across a freshly dead Great Diving Beetle by the side of the path. This diving beetle is one of our most impressive species, measuring in at a staggering 36 mm in length and quite chunky with it. I guessed that a passing car had hit this one sometime during the night. Great Diving Beetles are strong fliers and having spent the winter at the bottom of a suitable waterbody, this one had clearly emerged to search for a mate. Dispersal of these wandering adults mostly happens during the night and they can sometimes turn up at lighted windows (or moth traps) attracted by the light. Once the male finds his mate the pair will copulate – a process that can last for several hours – some time after which eggs will be laid.

Because this particular individual was dead there was no problem in handling it. A living diving beetle, however, can inflict a painful nip and the needle-like spurs on the legs can draw blood if the beetle is not handled with care. The beetle also has one other means of defence up its sleeve and this is a chemical one. In response to being handled a Great Diving Beetle will not only turn out the contents of its rectum onto your hand but it will also produce a milky fluid from glands on its prothorax. This fluid smells unpleasant and, remarkably, is made up of a cocktail of compounds which include certain steroids more commonly associated with vertebrate animals. For many would-be predators, notably fish, the compounds are distasteful and the fish will quickly release a beetle it has grabbed. It has also been discovered that some of the compounds act as neurotoxins and are sufficiently strong as to kill a number of would-be amphibian predators. Perhaps most surprising of all is the quantity of some of these vertebrate steroids in the beetles. It would, for example, require the adrenal glands from several herds of cattle if you wanted to extract a similar dose of the steroid cortexon to that found in a single beetle.

This particular beetle is the most widespread of the seven big water beetle species (those over 20 mm in length) and it can be found in many different types of waterbody. However, it has a preference for still or slow-moving waterbodies, so had probably emerged from the river, just a few yards away, or one of the lakes that are located a little further upstream.