Impacts of the wet year on Britain’s birds

2012 preliminary UK Nest Record Scheme (NRS) results from BTO

Full news report and tables from BTO here

Reed warbler. Photo by Mick DrydenThe BTO publishes preliminary results each Autumn to provide an initial assessment on the UK’s bird breeding season prior to the publication of the annual BirdTrends Report the following year. Producing results so soon after the breeding season is only possible thanks to NRS participants’ speedy submission of data.

Record-breaking rainfall

To say it was a wet spring and summer this year is an understatement. UK Met Office rainfall totals for England & Wales in two months were the highest on record, with four times the average falling in April and twice the average falling in June. If the adverse weather affected nesting birds, it also made life difficult for volunteers, resulting in many cancelled field sessions and missed nest visits. However, thanks to the dedication of the nest recorders, over 25,000 records were submitted in time for the preliminary report and 2012 breeding performance figures have been produced for 25 species.

Early breeders advance, late breeders delay

Conditions in February and March were actually warmer and drier than average, and many of the early resident breeders, including tawny owl, song thrush and long-tailed tit, commenced nesting significantly earlier than the five-year average. In contrast, long-distance migrants travelling northwards from their African wintering quarters the following month had to contend with a succession of severe weather systems across Europe and were greeted by cold, wet weather when they finally returned to their breeding grounds. As a result, laying dates of all six species for which preliminary results are produced were significantly delayed relative to the average for the preceding five years. Laying dates of short-distance migrants, blackcap and chiffchaff, which winter in the Mediterranean and therefore return to breed earlier, were no later than average.

Caterpillar-dependent residents struggle

Chaffinch. Photo by Mick DrydenFeedback from lepidopterists suggest that 2012 was a very poor year for moths and species that rely heavily on caterpillars as a source of food for their nestlings experienced a sharp drop in productivity. The average number of fledglings produced per breeding attempt for both blue and great tit was significantly below average, the latter experiencing the second worst season on record. This poor performance was influenced by small clutches and high failure rates during incubation, as well as by a reduction in brood sizes, suggesting that adults were in poor condition when breeding commenced. The number of chaffinch fledglings per nest was at its lowest level since records began in 1966, by some margin. Losses during incubation were high and heavy rainfall may have had a direct impact, wetting the eggs when the female left the nest to feed.

A poor vole year

Common kestrel. Photo by Mick DrydenMany of the lowland owls and raptors feed primarily on volves, which anecdotal evidence suggests were in short supply during 2012, although the extent to which this paucity was influenced by the adverse weather conditions is not yet clear. However, heavy rainfall almost certainly affects the accessibility of these prey items, making it difficult for birds to hunt. Fledgling numbers of all three species for which preliminary trends are produced (kestrel, tawny owl and barn owl) were below average, although this difference was significant only for kestrel.

Flooding and water-logging

Exceptionally high levels of rainfall directly impacted on those species whose nests are vulnerable to flooding. Reed warbler is the most obvious example, demonstrating a significant reduction in every aspect of its breeding success as a result of rising water levels in ponds and lakes, leading to a fall in fledgling production of almost 36%. Increased river flow may also have contributed to the increase in failure rates of dipper nests during incubation.

Poor prospects for fledglings?

Long-tailed tit. Photo by Mick DrydenThe results of the preliminary NRS analyses are broadly consistent with those of the BTO’s Constant Effort Scheme (CES), which calculates breeding success by comparing the numbers of adult and juvenile birds ringed each year at 120 sites across Britain & Ireland. However, there are some species (long-tailed tit, willow warbler) for which CES records a much more marked reduction in productivity during 2012. This difference suggests that young birds may have continued to struggle after leaving the nest, their lack of experience and relatively poor quality plumage making it much harder for them to cope with extreme weather conditions, leading to a drop in survival rates post-fledging.

Long-term impacts

Many of the species for which preliminary trends have been calculated are capable of producing large numbers of offspring each year, and so have the potential to bounce back rapidly following a poor breeding season provided conditions improve. However, the extreme conditions in 2012 resulted from a shift in the jet stream and it is difficult to predict how its position may be influenced by future climatic warming and the melting of the Arctic icecaps. If wet summers become more frequent, then we may witness long-term changes in the numbers of some bird species.

Now avian pox threatens our songbirds

Just when you thought things could not get worse, a new strain of avian pox is taking its toll on garden birds in Britain.

Great tit. Photo by Mick DrydenReport from Birdguides

A new report published this week online in PLOS ONE reports on the impact that avian pox is having on great tit populations. Avian pox has been recorded in British bird species such as house sparrows, blackbirds, dunnocks and wood pigeons for a number of years. However, the emergence of a new strain of this viral disease in great tits is causing concern amongst vets and ornithologists.

Wildlife vet Dr Becki Lawson from ZSL says: “Infection leads to warty, tumour-like growths on different parts of a bird’s body, particularly on the head around the eyes and beak. Although the disease can be relatively mild in some species, great tits suffer severe growths that can prevent them from feeding and increase their susceptibility to predation. Whilst a range of tit species are susceptible to this novel form of the disease, detailed monitoring of birds in Wytham Woods by scientists at the University of Oxford show that great tits are by far the most susceptible.”

“Although recovery from infection can occur, our results show that this new strain of avian poxvirus significantly reduces the survival of wild great tits and has particularly large effects on the survival of juvenile birds. Based on the numbers of affected great tits that we have observed at Wytham Woods, our models do not predict that this new disease will cause an overall population decline of the species. However, pox-affected populations have lower yearly growth rates. Hence, they are likely to have greater difficulty in recovering from other environmental factors that might reduce their numbers,” says Dr Shelly Lachish of the Edward Grey Institute at Oxford University.

With help from the public, scientists at the RSPB and ZSL have tracked the disease, which has spread rapidly in five years from southeast England to central England and into Wales. The annual seasonal peak of observed cases occurs in the early autumn months and incidents continue to be reported at this time of year. Genetic studies on the virus show that it appears to be the same strain seen previously in Scandinavia and more recently in central Europe, and is unlikely to have originated within Great Britain. BTO data on bird movements confirms that great tits rarely migrate outside the country. The spread of the virus to Britain is, therefore, thought to have occurred through the arrival of an infected vector, such as a mosquito.

Great tits are a particularly obvious bird at this time of year as many of them visit bird feeders. Numbers of great tits and blue tits do migrate into the Channel Islands in winter, especially during very cold weather on the continent. Please look out for any with obvious raw looking lesions and abscess-like growths often on the legs and face. There may be obvious lumps too under the feathers. If you see any birds that are affected please let the Société Jersiaise Ornithology Section know and information will be sent on to the authorities. It is unlikely that anything can be done for individual birds but it will be useful to monitor the disease’s progress in Jersey.

Two separate reports are available as downloads from PLOS ONE

Emergence of a novel avian pox disease in British tit species  download here

Epidemiology of the emergent disease Paridae pox in an intensively studied wild bird population download here



44 million birds lost in the UK since 1966

including an average of 50 house sparrows every hour…

Report from British Birds

Since 1966, the UK has lost breeding birds from the countryside at an average rate of a nesting pair every minute, say conservationists in The State of the UK’s Birds 2012, published on Monday 19th November.

House sparrow. Photo by Mick DrydenThe report estimates that there are 166 million nesting birds in the UK, compared with 210 million nesting birds in 1966. The house sparrow has seen one of the greatest losses of any bird in the UK. Although since 2000 house sparrow numbers have started to increase, the UK still has 20 million fewer sparrows than it did in 1966. The current population is estimated at around 10 million.

One of the report’s authors, Dr Mark Eaton of the RSPB said: “It is shocking to think that we’ve lost one in five of the individual birds that we had in the 1960s, especially when you think that the 44 million birds we have lost since 1966 is equivalent to the current adult human population of England and Wales.”

There have been many changes in the UK which have affected birds, most notably changes in the land use and the management of the countryside and seas – these can change the amount or quality of key resources needed by birds, such as suitable places to nest or a shortage of food in summer or winter. However, for some species, including the house sparrow, the precise reasons behind these declines aren’t fully understood.

Turtle dove in St Ouen's Bay. Photo by Miranda CollettThe changing fortunes of two, related species further highlight the changes to the UK’s birds: the turtle dove and the collared dove. In 1966, the turtle dove was still a widespread bird with about 140,000 breeding pairs, whilst numbers of the collared dove were very low, as the species only began nesting in the UK in 1955. Today there are only thought be around 14,000 pairs of turtle dove nesting in the UK, whereas the collared dove had exploded to around one million pairs.

Collared dove. Photo by Mick DrydenCold weather is thought to have had a startling effect on bird numbers too. The wren, for example – still the UK’s most numerous bird – has lost an average of 835 individuals a day since 2000. But another garden bird, the chaffinch, has increased at a rate of 150 individuals per day.

Dr Andy Musgrove of the BTO, who worked on compiling these figures, said “We have learnt a great deal about bird numbers in the UK and, particularly, how they have changed through time. Amongst individual species, whilst there have been some winners, the number of losers is greater and the long-term picture is sobering. There is still more to learn though, and we need the continuing support of ever greater numbers of volunteer birdwatchers, on whose efforts all of these numbers are based”.

The State of the UK’s Birds report is a great example of ‘citizen science’ in action. Most of the information upon which the report is based is derived from the efforts of a network of skilled, volunteer ornithologists who contribute to national monitoring schemes like the UK’s Breeding Bird Survey and Wetland Bird Survey. Such schemes provide a high quality evidence base underpinning the work of government, conservation organisations and land managers in their joint efforts to conserve the natural environment and its wildlife. Here in Jersey we too rely on volunteer observers sending in their sightings to the Bird Recorder at the Société Jersiaise Ornithology Section. We in turn compile an annual Bird Report each year (copies are available from The Museum in St Helier and from the Durrell Visitor Centre). The Ornithology Section also takes part in most of the UK’s bird monitoring schemes such as the Breeding Bird Survey and BIRDS ON THE EDGE includes a bird monitoring project. Channel Islands bird numbers are not included in The State of the UK’s Birds 2012 but the current status of Jersey’s bird populations can be seen in our own report Conservation Status of Jersey’s Birds: Jersey’s bird populations in the 21st Century.

The State of the UK’s Birds 2012 is produced by RSPB, British Trust for Ornithology and the Wildfowl & Wetlands Trust – and the UK Government’s statutory nature conservation. The report also includes the latest information on the number of ducks, geese, swans and wading birds spending the winter in the UK and an update on the internationally-important birds, including albatrosses and penguins, on the UK’s overseas territories.

The State of the UK’s Birds 2012 can be downloaded from the British Trust for Ornithology.

Chough report: October 2012

Report from Liz Corry

Captive choughs at Durrell

The two breeding pairs now in the display aviary appear to have settled in well. Arthur and Gwinny still come down for insects before the other two birds when keepers are present, but Tristan and Issy are by no means going without. There are four food bowls distributed around the aviary so everyone gets a chance to eat and enrichment food is also spread out.

During the heavy rains at the start of the month it was noted that Arthur and Gwinny were roosting out in the open. There is a large area of shelter at the back of the aviary, but the concern was that Tristan and Issy might have been defending the entire shelter. With that in mind keepers built two small shelters that were positioned either side at the front of the aviary. Food bowls were placed inside to encourage the birds to use the new areas. Occasionally keepers observe chasing between the pairs but this is to be expected.

Benvenuto Gianna

Gianna in quarantine. Photo by Liz CorryThe start of the month was an exciting time for Durrell staff as a new addition to the chough cohort arrived all the way from Italy. Staff at the University of Turin’s Faculty of Veterinary Medicine contacted Durrell during the summer regarding a juvenile chough they had hospitalised and wanted to re-home. They believed, through her very tame nature, that she had been taken from the wild as a young chick and kept in captivity and for this reason they could not release her back into the wild. They had, however, heard about Durrell’s captive breeding programme for choughs and wondered if she could be of use to the re-introduction project whilst also gaining a better quality of life.

Gianna, named by the staff in Turin, arrived on the 1st of October and stayed in the Les Noyers quarantine facilities until she had cleared her quarantine period. She weighed 260g upon arrival, slightly low for a female but expected after an overnight journey all the way from Italy. She was eating and drinking immediately and showed no signs of stress.

The Durrell Veterinary Department took blood samples and conducted a general health check during the first week in quarantine followed by weekly faecal screening. Once Gianna has cleared quarantine she will be moved to the display aviary to join the other choughs

NOTE it is presumed that Gianna is a different subspecies (P. p. erythrorhamphus) to the other birds (P. p. pyrrhocorax) and will not be allowed to breed with them. She will, however, be an invaluable asset to the flock.

Radio-transmitter trials

Attaching dummy radio tag. Photo by Harriet WhitfordAll of the choughs being released on the north coast this year will have radio-transmitters attached so their movements can be closely monitored. Standard tail-mounted tags supplied by Biotrack will be fitted to each bird once they move up to the release aviary. Tail feather attachment means that the tags will fall off naturally when the birds moult, thus reducing stress. In order to assess if the tags have any impact on the birds’ health and/or Attaching dummy radio tag. Photo by Harriet Whitfordbehaviour once attached we are trialling dummy tags on two choughs in the Wildlife Park. This trial also allows us to test the durability of the tags, especially important considering the inquisitive nature of the choughs!

B6975 (♀) and B6976 (♂) were taken to the vets to have the tags attached and then released straight back into their aviary. Upon release, B6975 was observed preening and Attaching dummy radio tag. Photo by Harriet Whitfordtaking an interest in the antennae of the tag, but soon lost interest. She was caught up four days later to check her health and the condition of the tag. The tag was still intact although there had been extensive pecking at the glue used to attach the tag to the feathers. Her health and that of the other bird seem at present to be unaffected by the tag.