Saturday, 11 October 2014

A question of time

Many of conservation’s headline figures, which underline pronounced population declines for various plants and animals, come from monitoring datasets that extend back over just a few short decades. Declines in our farmland bird populations, for example, which are evident from a dataset that extends back to the 1960s, pick up the impacts of agricultural intensification that began in the late 1970s. Such declines are alarming, illustrating how the changes we make to the landscape can quickly impact on other species.

There is, of course, a wider context to these changes and it is important to realise that the headline figures do not always tell the whole story. Still using farmland birds as an example, it is apparent that our countryside is no longer suitable for a range of species, their populations now at much lower levels than they were before the Second World War. Go back a century beyond this, however, and things would have been different again, though not necessarily in the ways that you might expect. Some of our ‘farmland’ birds are species that benefited from the development of arable systems, their numbers increasing as new opportunities emerged. Now those opportunities have gone, their numbers have fallen back. The barn owl provides an example of a species whose population increased as farming systems developed – it used to be more common than the tawny owl – but which then declined from the late 1800s to the numbers we see today.

This does not mean that we shouldn’t be worried about the declines we have seen over recent decades. If anything, we should be more concerned because of the speed of change that is taking place. All of the changes that humans have made to the landscape – extending right back to when we first arrived in Britain – have had some impact on other species but it is the scale of the current impacts that is particularly alarming.

The increasing tendency to focus the conservation debate within economic arguments, giving wildlife and the ‘services’ it provides a measurable economic value, is a particular concern. It removes the moral responsibilities we have to consider how our activities impact on the other species with which we share this land. Taking more for us leaves less for them, no matter what the timescale.

Friday, 10 October 2014

Weather delivers a good run of migrants

The beginning of October can prove either incredibly exciting or very frustrating if you happen to be a birdwatcher. While it is the time of the year when most of our migrants are on the move, the prevailing weather conditions ultimately dictate where and when they might turn up. If the winds are from the west then Norfolk’s east coast is unlikely to turn up anything unusual. If, however, the wind is from the east and there is overnight rain or fog on the coast, then huge numbers of migrants may make landfall, delivering a veritable feast for the birdwatcher.

This autumn has got off to a good start and there have been some good numbers of migrants reported from across the county. Most have been familiar and expected species, like wryneck, yellow-browed warbler and red-backed shrike, but there have been one or two less common species. More of the action has been taking place further north, however, particularly in relation to rarities, and it has been the Northern Isles, Shetland and Orkney that have hosted the best birds so far. Included in these have been a number of American species, transported across the Atlantic within the fast-moving tracks of autumn storms.

October is traditionally the month when many birdwatchers head west, journeying to Cornwall and on to the Isles of Scilly. These small islands provide the best opportunities for catching up with some of the rarest vagrants and they also provide the added benefit of some late season warmth, extending the summer for a few more weeks. For the more hardcore birdwatchers – those seemingly more interested in the number of species they have seen – the autumn migration becomes a bit of game. Should they remain on the mainland, ready to dash to Norfolk or head to Scotland, or should they base themselves on the islands, where a rare bird might only make a fleeting visit before disappearing, never to be seen again?

As someone who is more interested in watching the birds on my local patch or in engaging with a bird within its wider landscape, autumn is a less pressured, more enjoyable affair. I can savour what happens to come my way and if it does come? Well, then it doesn’t matter.

Thursday, 9 October 2014

Brown trout ready to spawn

I tend to think of this as the ‘otter bridge’. After all, for a while this was the place to come and watch for the Thetford otters. I’ve not seen the otters here for some time, although I occasionally stumble across them elsewhere on the rivers that skirt the margins of town. Perhaps that’s a good thing now that several sizeable brown trout have stationed themselves upstream of the bridge, where a bed of gravel lips a deeper pool.

It seems likely that the trout will use the gravel bed for spawning and one individual in particular appears to have already claimed his patch. From the bridge you can watch him as he lunges at those tempted to trespass. It is perhaps a little early for the trout to have started spawning but it will not be long before the gravel hosts many hundreds of eggs, each just a few millimetres in diameter. Peak spawning in UK waters falls during late October or early November but, since it is influenced by the weather and by water conditions, it may continue well into the New Year. Depending on when the eggs were deposited and the temperature of the water, the eggs are likely to hatch from mid-March. Since the proportion of eggs successfully fertilised tends to be high, large numbers of fry emerge, most of which will fall to predators.

All of our native populations are descended from colonisations that occurred soon after the end of the last glaciation and most of our rivers and streams host brown trout populations. This is a pattern repeated across much of Europe and western Asia. Some of those trout that inhabit our lakes make an autumn migration into feeder rivers and streams, seeking out pure, fast-flowing water running over the deep gravel beds used for egg-laying. It is the female trout who makes one or more scrapes within these gravel beds, each of which is known as a ‘redd’. Spawning is a stressful time for trout and many will be taken by predators, die from exhaustion or succumb to the effects of disease. It would be nice to see the otters but I suspect that the trout would make easy pickings while they remain so focused on spawning.

Wednesday, 8 October 2014

Kestrel no longer so commonplace

Writing in early 1917 and far from home, the poet Edward Thomas noted how the sight of four or five planes ‘weaving and wheeling overhead’ reminded him of the kestrels that he used to see over the Shoulder of Mutton Hill near Petersfield. Such recollections rekindle my own memories of days spent near Petersfield and of the kestrels that would haunt the skies, scanning the ground below for small mammal prey.

Throughout my childhood the kestrel was regarded as our most commonly seen bird of prey, a familiar species that I was certain to see from a car journey of any distance. Long-term monitoring data from the British Trust for Ornithology (BTO) support this, showing the kestrel population of the mid-1970s to have recovered from the effects of organochlorine pesticides and to be at a peak not since matched. This peak was, however, short-lived and there was a substantial decline over the following decade, which left numbers well below the level that had been achieved. This new decline has been driven by a period of agricultural intensification that left our farmland much changed. The loss of many thousands of miles of hedgerows and field margins brought about a decline in the numbers of small mammals and large invertebrates upon which our kestrels depend.

We are not alone in having lost so many kestrels; it is a pattern repeated more widely across Western Europe, underlining how the changing demands we have for cheap food, produced in ever increasing quantities, have changed the landscape fundamentally. With less space for wildlife it is inevitable that those species at the top of the food chain will show pronounced changes in their numbers and abundance. The pattern of change seen in our kestrel populations shows some regional variation; for example, the species benefited during the period of afforestation, where many hundreds of hectares of coniferous plantation were established. However, as these new forests developed so they shaded out the swards of rough grassland between their ranks and with this loss went the field voles and their kestrel predators. The kestrel remains common enough to remain familiar and to haunt the texts of today’s nature writers. Let’s hope it remains a living part of our countryside and not one consigned to our literary heritage.

Tuesday, 7 October 2014

Making a splash

Rain this heavy seems out of keeping with the season, catching me unexpectedly as I make my way home. A dry towel and a change of clothes, quickly followed by a warming mug of tea, soon restore inner warmth that had been lost through soaked clothes. As I drink my tea I watch the rain continue to fall. From the kitchen window I can see the heavy drops splash onto the surface of the patio, which dances under the deluge. It is then that I spot the first frog, sat with its head slightly raised amidst the downpour. It soon becomes clear that this frog is not alone and that there are several on the patio, with others emerging from under the shed or from inbetween the flowerpots. Can there really be this many frogs using this small part of the garden?

I am interested that the rain should have tempted them out in such numbers. I have seen the occasional frog on damp summer evenings but they have not seemed that common in the garden this year. That they should be here in such numbers takes me aback but it does remind me that there is plenty of food here to support them – the garden is on chalk and over-run with slugs and snails – even though it is in the centre of town.

The common frog is one of the few amphibian or reptile species to penetrate our larger conurbations. There is, however, good evidence that much of this penetration has been achieved with outside assistance. The fondness that we have for sharing frogspawn with friends and relatives may explain how frogs have been able to cross the ‘concrete jungle’ to colonise newly-created ponds. While the ponds are the focus for breeding activity, for much of the rest of the year these urban frogs will be living a terrestrial existence, largely out of sight. During the day they hide up in sheltered corners, such as under the shed, before emerging at night as the humidity increases. A sudden rainstorm and the associated drop in temperature may bring them out earlier, much as it does the molluscs and earthworms upon which they feed.

Monday, 6 October 2014

Garden spiders enjoy a good summer

There is every indication that the garden spiders, hanging head down and motionless in the centre of their orb-webs, have had a good summer. I am not alone in noting just how many there seem to be around this autumn, the topic forming on the lips of many a conversation over recent weeks. From the patio I can count a dozen or more webs, each with the corpulent form of a female garden spider, Araneus diadematus, at its centre. Each of these females has reached maturity and will have gone through eight moults, shedding the patterned exoskeleton to grow in size. The smaller males, which sit separately within their own triangular webs, undergo fewer moults.

The garden spider is a common and widespread species, found across Britain and within a range of habitats beyond the gardens with which it is most often associated. A closer examination reveals bold patterning and a white cross, carried on her back. The presence of the cross made this spider an object of veneration during the Middle Ages and may be one reason why this is the spider that features most often in book illustrations.

As with many other spiders courtship is a rather dangerous affair for the males, each of which has to convince the female whose web he has entered that he is a suitor and not a meal. The male approaches the female with great caution, playing the threads of her web to signal his approach. More often than not the female will lurch towards the male, prompting him to let go of her web and drop away, his fall broken by the safety line that he will have anchored to the edge of her web. After several attempts the male will either have successfully tamed and mated with the female or been taken as prey. The female will remain in the web over the coming days, receiving more suitors, before leaving in October to lay her eggs nearby. These are protected with a dense covering of silk, slightly yellow in tone and with the appearance of cotton wool. Her work done, the female will remain beside the eggs. No longer feeding, her life ebbs slowly away and the cycle begins over again.