Saturday, 16 December 2006

A touch of the winter blues

I always find this time of year rather difficult; the damp clinging cold and drab skies do little to lift my spirits. As a morning person I resent the way in which the dark of night intrudes into my routine and limits the time that I can spend out before work. While crisp, bright winter days invigorate me, the still, overcast, rain-sodden days of late provide little in the way of cheer as I trudge along the river on my way to work. The moorhens skulk about in search of food, hunched forward as if they too are weighed down by the cheerless weather. There is, however, a spot of colour in this flat and featureless scene – a kingfisher which frequents this stretch of the river.  A dazzling, darting streak of electric blue that whirls away from me as I near its favourite perch; this kingfisher must nest nearby, remaining on its territory throughout the winter months. I remember reading somewhere (perhaps in David Boag’s wonderful book on the species) that only the righteous may witness the kingfisher. It is certainly true that, despite its bold colours, this bird is often overlooked. One reason may be its size – the kingfisher is about the size of a greenfinch, a fact that will surprise many who would imagine, never having seen one, this to be a larger bird.

I have been fortunate enough to see kingfishers in the hand, since we sometimes catch them in our nets when out bird ringing. With their short, waxy, orange feet, orange-brown underparts and electric blue-green upperparts they are incredibly beautiful. They are also very docile when being handled and move their head very slowly (like some kind of automaton) to view the proceedings. The colourful plumage once proved popular with milliners and the feathers would appear incorporated into hats. Other birds were shot for taxidermy and many were stuffed by Victorian taxidermists.

The kingfisher population has flourished over recent decades on many stretches of river. Improving water quality is likely to have played a part but it is the run of mild winters that will have had the greatest impact on the population. Very cold winters, during which the slow-moving lowland rivers favoured by kingfishers may freeze over, can spell disaster. During the winter of 1962/63, the severe cold resulted in the complete loss of kingfishers from some areas and in many others the population fell by 85%. Fortunately, kingfishers are able to produce two or three broods of young a year and so populations can bounce back quickly. While I might favour the crisp chill of a proper winter’s day, I will tolerate the damp, gloomy weather for the sake of this wonderful bird.

Friday, 15 December 2006

The sound of the countryside

For me, being out and about in the countryside is not just about what you see. It is also about what you hear, feel, smell and taste. The churring of a nightjar in the still of the forest, the rough texture of bark or the scent of fungi on a damp autumn morning. You should be able to engage with nature and immerse yourself in the world around you through all of your senses. But what if you are unable to use one or more of your senses; does this diminish your experience of nature? For most of us the answer is unknown, although we may experience some degree of loss as we age and our eyesight and hearing begin to fail. It has been calculated that roughly one in every seven people suffers from some form of hearing loss and many older birdwatchers comment on how they can no longer hear the high pitched calls of goldcrests or the echolocation of feeding bats. As I age, I wonder if I too will reach a point where I can no longer hear (and enjoy) these subtle sounds.

In an attempt to help hearing-impaired visitors engage more fully with wildlife, Norfolk Wildlife Trust has recently added a ground breaking new hearing support system to one of the hides at its Cley Marshes reserve on the North Norfolk coast. Two microphones positioned on the reserve pick up the sounds of the waders and wildfowl that use the many pools. These sounds are then fed back to the hide, where they can either be heard on headphones or via a hearing loop. Although similar systems have been employed elsewhere, the one at Cley is unique in that it is powered entirely by a combination of solar and wind power; a suitably green solution.

The system was developed by Dennis Furnell, who was himself partially deafened as a result of a car accident. Thanks to a grant from The Heritage Lottery Fund, plus equipment donations, Dennis has been able to install the system as part of Norfolk Wildlife Trust’s “Access for All” project. This also involves the production of large print leaflets for all their major reserves and an audio trail around Cley Marshes itself. Such developments are a welcome addition to what is already one of the country’s premier places to engage with a diversity of wildlife. Wildfowl and waders can be noisy birds, particularly when present in flocks several hundred strong. More people will now be able to enjoy the sights and sounds of this part of the Norfolk coast and, hopefully, feel that they have truly engaged with the birds and other wildlife that make the countryside such a special experience. 

Thursday, 14 December 2006

A Christmas tune

The dark gloom of these December mornings is softened somewhat by the wistful tunes of singing robins. While all our other songsters have fallen silent, the robin continues to sing in defence of its territory right through the winter months. Holding a territory is incredibly important for a robin and it is only during the most severe of winter weather that the pattern of territories may break down altogether. Even the females may set up their own winter territories, often close to where they will breed the following season, and proclaim ownership of these through song.  The winter song contains certain phrases that denote territory ownership and these also appear in the subtly different breeding season song. What are missing from the winter song though are the sexual phrases used in establishing a bond with a mate.

There is a strong tradition associating this confiding and popular bird with Christmas and it is always interesting to see how many Christmas cards arrive with a robin on their cover.  In fact, robins first appeared on cards soon after the custom of sending them at Christmas first took off commercially back in the 1860s. David Lack, writing in his famous book ‘The Life of the Robin’, noted that the use of the robin on Christmas cards probably stemmed from similarity of the robin’s red breast to the bright red uniform worn by Victorian postmen; many of the early card designs showed a robin with an envelope in its mouth.

Despite its confiding nature, and our enduring affection for this bird, it is worth noting that the robin can be a particularly quarrelsome species. The territorial song and red breast are important components of a display used to deter other robins from trespassing on an established territory. While the song proclaims “this is mine, stay away”, the red breast is used in more direct encounters. During a territorial dispute two robins will begin by singing at each other, with the territory owner attempting to sing from a higher perch than the intruder. This enables him to show off his red breast to maximum effect. If, for some reason, the territory holder finds himself positioned below the intruder he will throw his head back, again to maximise the amount of red breast on display. Such displays are usually sufficient to see-off the intruder but, if not, a ferocious fight may break out. The red breast is so important in this pattern of behaviours that a robin will even attack a bunch of red breast feathers. So, as the season of goodwill approaches – with the robin as its symbol – it is worth remembering that our beloved national bird has another side to its character.

Wednesday, 13 December 2006

Who rules the roost

Now that the birds are beginning to return to my bird feeders, I am reminded of the hierarchy that exists within this avian community. As tits, finches and the occasional house sparrows jostle for position at the feeders, it soon becomes clear who are the bullies in this outdoor dining room. Size plays a role; great tits oust blue tits from favoured perches and, in turn, the blue tits see off the smaller coal tits. In fact, the coal tits seem to prefer to sneak in, grab a sunflower heart and then beat a hasty retreat to eat their meal elsewhere; a sensible strategy for a bird at the bottom of the pecking order. Not so the greenfinches who dominate the feeders, each one seemingly picking through the hearts to select the plumpest seed. These aggressive birds force their way onto the perches and then turn noisily towards any birds that try to usurp them.

Even within a species there exists a clear hierarchy. Top of the tree, so to speak, are the adult males and it is to these that the females and younger individuals defer. The hierarchy is maintained by a series of threats and displays and only rarely does a dispute turn physical. From a biological perspective it makes sense for two individuals to settle their differences in a non-physical manner. In the harsh reality of the natural world, any injury that results from conflict has the potential to be life threatening and, with such high stakes, it is better to resolve a dispute without bloodshed. Birds and other animals use display to warn a potential opponent of their strengths. As such, an inferior individual can assess if it has bitten off more than it can chew by facing up to an individual that is likely to win a physical contest.

One of the interesting results of such dominance hierarchies is that individuals from lower down the pecking order may be forced to feed in circumstances that are less than ideal. Work carried out a number of years ago illustrates this point rather well. Researchers put up a number of bird feeders in different locations within a garden, with some feeders positioned in cover provided by thick shrubs and others placed out in the open, where the risk from sparrowhawk predation was much higher. The researchers then watched to find out how the feeders were used by great tits of different ages and sexes. While the dominant adult males chose to use those feeders placed by cover, younger individuals were forced to use those positioned in the open. The same thing will be going on in your garden so spend some time watching and all will be revealed.

Tuesday, 12 December 2006

Bedding down for the winter

The mild November weather had its effect on our wildlife, with very late sightings of certain butterfly species and reports of hedgehogs still on the go. Most hedgehogs build their winter nests during October and are safely tucked-up by mid-November. However, winter hibernation remains a flexible option for our hedgehogs and many will continue to remain active if conditions (both in terms of temperature and food availability) are suitable. It is a common misconception that hibernation is an extended form of sleep, during which the body is rested. Instead, it is a complex behaviour used to conserve energy during periods when the animal may be faced with highly unfavourable conditions.

Since keeping warm is an energetically expensive strategy during winter, the hibernating hedgehog abandons this, allowing its body temperature to fall. This controlled reduction in body temperature, typically brings the animal’s temperature down to within a couple of degrees of the ambient temperature. If the ambient temperature falls to dangerously low levels, which would cause the hedgehog to literally freeze to death, then the hibernating hedgehog will burn off more of its body fat to generate the heat needed to keep the body temperature at a safe level.  This controlled reduction in body temperature results in a fall in oxygen consumption, heart rate and breathing rate, together with a restriction in the amount of blood flowing to the major organs. While an active hedgehog may have a heart rate of 250 beats per minute (bpm) this falls to just 5bpm during hibernation. Research has shown that hedgehog hibernation is most efficient at 4ºC and one of the features that helps the hedgehog operate at around this temperature is the winter nest itself. Made predominantly from leaves, pushed up against a larger object, the nest provides protection from the worst of the winter weather. Temperatures within the nest typically remain between 1 and 5ºC, ideal for hibernation.

Hibernation is not continuous and a hedgehog will “wake-up” every 7-10 days. This takes between three and four hours and the hedgehog will normally remain within the nest for a short period before re-entering hibernation. Very occasionally, individuals will venture outside, perhaps to establish a new winter nest. These periods of arousal are energetically demanding, collectively accounting for 80% of the energy expended during the entire hibernation period. As such, they must be important for the hedgehog. Fat reserves fuel hibernation and these are laid down prior to hibernation and need to be sufficient to last the winter. Any young or undersized hedgehog weighing less than about 1lb (450g) is unlikely to survive more than the briefest period of winter weather, so should be rescued to a hedgehog rehabilitation centre.

Monday, 11 December 2006

Red signals danger for our crayfish

With the recent rain it is hardly surprising that the river is running so high. Still, it is a bright start to the day and I am optimistic that we will catch up with some crayfish, thanks to our trap and a punctured tin of cat food. We have just one native species of crayfish here in Britain, the white-clawed crayfish, but our chances of seeing this species are pretty slim on this stretch of river. Instead we are likely to see a good number of the larger signal crayfish, a menacing introduction from North America. While our native is a relatively small species, usually less than 10cm in length, the signal crayfish can reach 30cm. Bigger, aggressive and able to produce more young, this American interloper poses a real threat, something that is made worse by the fact that it can carry a virulent disease called crayfish plague. This disease seems to have little effect on the signal crayfish but it has contributed to drastic losses of native crayfish from many of our rivers.

A number of non-native crayfish species have been farmed here since the late 1970s and, perhaps inevitably, they have broken out and established themselves in the wild. Here they can occur in such incredible densities that their burrowing activities undermine river banks and flood defences. The threat from these alien crustaceans has now been recognised; the white-clawed crayfish has been listed as being globally threatened and research is underway to establish how the non-native species can be controlled and removed.

The Brecks Countryside Project is coordinating the research work being carried out locally. This work examines ways by which introduced species can be controlled through trapping; exploring different types of traps and bait, and looking to see if regular trapping has any impact on the size or structure of the crayfish population. The traps that we were on our way to examine the other morning were part of this project. Hauling them out of the water, it was clear that the signal crayfish were still very active at the site even this late in the year. The two traps held 29 crayfish, all signal. Each individual was sexed and measured, and then notes were made of the water temperature and flow rate. The mild conditions overnight had prompted the crayfish to venture out in search of food and the cat food would have proved highly attractive. This local scheme is a partnership between the Lark Angling & Preservation Society, the Brecks Countryside Project and The Environment Agency. Just coming to the end of its first year, the project has already generated some very useful information and it seems likely that more will follow next year.