A bad year for owls

It appears that 2006 has not been a very good year for our breeding owls. The latest information to have been published by the British Trust for Ornithology’s (BTO) Nest Record Scheme, suggests that many tawny owl nest sites were unoccupied this year. Tawny owls start nesting early in the year, with breeding territories established during the first part of the winter (which is why you may hear them calling now). A combination of food availability and weather conditions will determine if they then go on to breed. It appears that last winter there was simply not enough small mammal food around for many pairs to get into breeding condition and so they gave it a miss.

Barn owls, of which Norfolk holds a sizeable population, fared slightly better, with occupancy rates at monitored sites only down by a small amount. However, high levels of chick mortality and small brood sizes at fledging suggest that even these enigmatic birds were struggling to find sufficient food for their growing chicks. Even so, our barn owls fared somewhat better than those in the southwest of the country, where very few pairs managed to rear their broods of downy youngsters.

Such short-term failures in themselves are not necessarily going to have a long-term impact on the owl population, especially for a species like the barn owl which has tremendous reproductive potential. If 2007 proves to be a good year, with abundant food and good weather, then they should make up their losses. It is for this reason then, that the BTO monitors breeding success each year, extracting long-term patterns which may signal that a species is in difficulty. If a species shows a significant long-term decline in breeding success over many years then the BTO can issue an alert, warning the Government’s conservation advisors that there is a problem. The Nest Record Scheme’s current alert list contains 21 different species. Included in these are familiar birds like kestrel, which has shown a significant decline in brood size (the number of chicks in the nest) since 1990. Also included are the barn owl and bullfinch; the latter has, since 1990, experienced increased levels of nests failing at the egg stage. Could this be due to predation?

While the reasons for the patterns seen in individual species may differ from one species to another, there may also be underlying causes linked, perhaps, to global climate change (we know that many species are nesting earlier now than they did 20 years ago) or to changes in the nature of our countryside. As such, it is essential that we continue to monitor breeding success and to identify those species that need conservation action.

Woody's return

Back in June I wrote about the launch of a new survey, set up to establish the extent to which great spotted woodpeckers make use of gardens during the breeding season. The survey was a collaboration between the British Trust for Ornithology (BTO) and Radio 4’s “Shared Earth” programme (which is back on our airwaves for a second series today at 3pm).

The results of the survey have just been announced and they make very interesting reading. Reports were received from gardens across the country, including a number from here within Norfolk. Collectively, the contributions have enabled researchers at the BTO to build up a detailed picture of just how the woodpeckers change their use of gardens as the summer progresses. Early on in the season, from late June, adult woodpeckers begin to increase their use of garden feeding stations – arriving to tuck into peanuts and fats. The results suggest that males make greater use of this resource than females, something which almost certainly reflects the fact that females typically remain in the nest cavity during daylight hours, tending to their eggs or young chicks. During this period the male brings food to the female so she does not need to visit garden feeding stations. This pattern continues for several weeks and then, from early June, adults begin to arrive with youngsters in tow. These young great spotted woodpeckers can be separated from their parents by the red cap covering the top of their head and by the fact that the area of red under their tail is rather pale, seemingly appearing washed out. The adult male has a small patch of bright red at the back of his head and bright red underneath his tail. The female also has this patch of red under her tail but lacks the patch on the back of her head, all very useful features when it comes to working out just who is visiting your garden. Adults continued to arrive with their young over the following weeks but then left them to visit on their own. Having introduced their young to a suitable feeding opportunity their parenting was done.

Another aspect of the study looked at the extent to which these birds break into nestboxes containing broods of young tits. Many people do not realise thay the great spotted woodpecker is a predator of other birds’ nests but the study showed that many of those participants with a nestbox in their garden had experienced such predation. There are also reports of woodpeckers breaking into the mud nests of house martins to reach chicks.  It seems that the great spotted woodpecker is a resourceful bird, able to make the most of opportunities.

The tuneful Snipe

A crisp and bright November morning proved ideal for watching the flocks of duck and waders on the pools at Cley. Shoveler, wigeon and teal were busy bathing, while godwits and redshank probed for food, and gulls loafed about on the exposed mud. Only occasionally was this tranquil scene disturbed by the noisy arrival of another flock of brent geese or by the passing attentions of a hunting marsh harrier. The good light enabled me to spend some time studying one of the less obvious users of the pools, a snipe. These stunning little waders have dark, richly patterned plumage and are most often encountered by chance. Flushed from beneath your feet in some patch of wet meadow, they explode into the air with a hoarse call. A low zig-zag flight takes them away before the bird rises steeply up into the sky. Such brief views do not provide the time to appreciate the stunning plumage, so a bird feeding in the open at Cley is an opportunity to be savoured. It is worth noting that snipe sometimes perch on fence posts during spring and early summer – an even better opportunity to see them.

The most striking feature has to be the snipe’s bill. Long and straight (proportionally, it is the longest bill of any European bird), it is perfectly suited to a life spent probing the wettest margins of pools and the dampest of wet meadows. Here it feeds on earthworms and other soil-dwelling invertebrates. The loss of such habitats, through long-term drainage and changes in habitat management, has caused breeding populations to decline at an alarming rate. Norfolk’s breeding population has certainly declined, by 86% between 1992 and 2000 according to one set of figures, but the winter population is larger, swelled by the arrival of birds from further north and east.

The snipe, like its relative the woodcock, is known for its breeding display. Descending rapidly from a high flight, the bird produces a bizarre sound. Lasting for only a few seconds, the sound is best described as a fluting bleat. The noise itself is made by the air passing over the outer pair of tail feathers, which are held out away from the rest of the tail. The slightly opened wings help direct air over these tail feathers, which then vibrate to produce the sound. At the beginning of the last century there was much debate among British ornithologists as to how this sound was made. However, in 1912, Philip Manson Bahr, lecturing to the British Ornithologists’ Club, inserted two outer tail feathers into a cork, attached to a length of string. By whirling this around his head he was able to recreate the noise and halt the debate.

Heron drops by

We had a new bird in the garden last week - a grey heron. Although not the most popular of visitors for some, we were delighted to see such an impressive bird. The heron was perched on a wall; stiff and erect, it was alert to any danger but seemed uneasy within such urban surroundings. It must have been attracted by the presence of three ponds, one in each of the neighbouring gardens. At least two of these are free of fish, designed as they are with wildlife in mind, so it seemed unlikely that the heron would find them quite as attractive as they may have appeared from the air. Perhaps sensing this, the heron laboured up into the air after a few minutes to disappear behind neighbouring houses.

Herons have done well in recent years, their numbers increasing thanks to a run of mild winters. Cold winters, leading to frozen waterbodies, can spell disaster for herons, isolating them from their feeding grounds and increasing mortality levels within the population. The influence of winter weather on the heron population has been documented thanks to the British Trust for Ornithology’s annual Heronries Census. The study has been carried out annually since it was launched in 1928 by the late Max Nicholson, making it the longest running study of a bird population in Britain (and possibly the world). Although many heronries contain just a few nests, some can contain dozens or even hundreds. I used to live next door to a small heronry at Wolterton Park, to the north of Aylsham. Each spring, the ekk ekk ekk calls of the young herons could be heard, as they demanded food from their parents. The ground beneath the colony was splattered with droppings and pellets, the latter containing the coughed-up hard remains of unfortunate fish, eels, voles and amphibians.

Nowadays, I tend to see herons on the coastal marshes or along the river valleys well inland but, as my recent sighting shows, they will also visit garden ponds, a habit that can cause consternation for some. Discouraging herons from taking fish is not straightforward. A net covering the entire pond is the only truly effective deterrent.  Plastic herons, sold on the notion that having one by your pond will discourage a “real” heron from visiting, are useless since herons are not territorial and will often feed communally. Intersecting wires, placed a foot or so off the ground around the pond, may work because herons do not like stepping over objects. Of course, you could just add more cover within the pond itself, accept that you may lose the occasional fish, and enjoy the sight of such an impressive bird.

Harlequin poses threat to natives

Over the last few days I have spotted an increasing number of harlequin ladybirds. Normally I would be delighted to see a ladybird but the harlequin is not one of our native species. Instead, it is a potentially troublesome and invasive addition to our fauna, reaching our shores because of our own actions. Let me explain. The harlequin ladybird is a native of eastern Asia but it has been introduced to a number of countries as a biological control agent. Scientists, looking for an alternative to pesticides, have used the harlequin to control crop pests, such as aphids and scale insects, by introducing them into glasshouses, crops and even gardens. Unfortunately, as has been the case for a number of species used in this way, the harlequin has gone on to become a pest in its own right. It first established itself here in Britain in 2004, with individuals arriving from the Continent (where they had been introduced) thanks to their remarkable powers of dispersal or by gaining assistance in shipments of plants and other foodstuffs.

The harlequin ladybird is pretty catholic in its choice of habitats but does seem to favour deciduous trees like sycamore and maple. Here it feeds on aphids, scale insects, the eggs of various moths and a range of other insects. This species has a clear competitive advantage over most of our native ladybirds because it has a much greater breeding potential. The pre-adult stage lasts just 20 or so days (although this is temperature dependent) and, once they reach adulthood, the females can begin to lay eggs after just five days. This means that a single female can produce more than 1,000 eggs during her lifetime.

At the moment, the numbers of harlequins in Britain have not reached the pest proportions seen elsewhere in the world. In North America, many tens of thousands may overwinter in a single home and, given their tendency to bite, they are not the most welcome of lodgers. They are also a threat to our native species, especially when aphid numbers are low, as the species is likely to feed on other ladybirds and their larvae. Even wine production could be threatened. Harlequins are attracted to soft fruit, like grapes, and may occur in such numbers that they taint the resulting wine production with the alkaloid chemicals they carry to deter potential predators.

Fortunately, the Government has provided funding to the Harlequin Ladybird Survey Project (see www.harlequin-survey.org) to collate information on sightings and to undertake research to assess the level of the threat. It is also hoped to determine how the species may be controlled to prevent it becoming a pest. Let’s hope the research comes up with a solution.

Autumn storm forces Little Auks south

The start of November saw strong winds in the North Sea. Combined with the high tides, these brought flooding to parts of the east coast and a flight of little auks, pushed south from their more normal wintering haunts on the northern oceans. Reports of these tiny birds, no larger than a starling in size, came from along the north and east coasts of Norfolk. Most were seen passing close inshore but a few were found on coastal waterbodies or downed on the beach. One birdwatcher, who I met at a talk I was giving in Lowestoft, told me about one unfortunate individual taken by a great black-backed gull; the gull took several attempts before managing to swallow the auk whole.

The little auk is possibly one of the most numerous seabirds in the world, with a breeding population numbering many millions. The species breeds in the high arctic, nesting on rocky scree slopes on islands like Svalbard, Bear Island and Greenland. Individuals leave the breeding colonies in August, just as the sea ice is beginning to form. The birds then spend the entire winter at sea, where they form very large flocks which feed on small crustaceans and fish. These flocks can be found from the edge of the pack ice, south to the Gulf of Maine in the west and the northern North Sea in the east. Only when strong winds and sea conditions work against them do they get pushed further south to reach the Norfolk coast. In some years, very few little auks are seen off the coast of Norfolk – for example just seven were seen in 1994 – but in other years many thousands may be reported. The years when very large numbers are forced south are known as “wrecks” and it is during such events that individuals can be blown inland. In 1895, a huge “wreck” resulted in reports as far inland as Thetford and, across the county, some 250 were said to have been stuffed by taxidermists. Many of these storm-blown birds appear underweight and it is thought that poor feeding conditions may also drive the birds southwards.

I will never forget the first little auk that I saw, some 15 or so years ago. This wind-blown individual was swimming about in one of the channels that run at right angles to the east bank at Cley. The small, dumpy bird moved about as if it were a clockwork toy. The head and tail ends of similar shape reinforcing this image and suggesting that it might swim equally well backwards as forwards. Mind you, it is worth remembering that this tiny bird can survive a winter spent in the middle of the vast northern oceans.