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Where have all the birds gone?

Posted on December 2, 2011 | 5 comments

There are virtually no birds in my garden at the moment, and they have been conspicuous by their absence all through the autumn. This appears to be a more widely observed phenomenon as reported on BBC’s Countryfile, and the RSPB have been seeking to reassure people who are concerned by the apparent dearth of birdlife visiting their gardens that it’s simply due to the abundance of suitable food still accessible in the countryside, and whenever possible that’s where the birds prefer to be.

I can vouch for the disappearance of the small birds from gardens. Apart from the occasional blackbird and blue tit (and a jay last week – the first one I’ve ever seen in my garden!) very few birds are availing themselves of my feeders. If this is happening in your garden the best thing to do is to keep your feeders clean and put a small amount of feed in so any passing birds recognise your garden as a source of food and can stop to refill if they need to. But it looks as thought the cold weather is starting to arrive here in Cambridgeshire so garden bird numbers may well increase in the near future.

So last weekend I ventured to the fields on the edge of Histon to see if they are still in residence. The hedges and fields were well populated with goldfinch (Carduelis carduelis, Dansk: stillits) and chaffinch (Fringilla coelebs, Dansk: bogfinke), great tit (Parus major, Dansk: musvit) and long tailed tit (Aegithalos caudatus, Dansk: halemejse) and green woodpeckers were abundant too. I don’t know if the numbers of green woodpecker (Picus viridis, Dansk: grønspætte) I see are representative of national trends but they seem to be numerous here in Histon, also where I work on Cambridge Science Park and today I was at the RSPB reserve at Fen Drayton near St Ives and there were good numbers there too. Two birds that I haven’t seen recently in the numbers I’d expect are dunnock and greenfinch – I hope that’s because they’re out in the countryside and it doesn’t reflect a decline in overall numbers.

I talked in my post a couple of weeks ago, Forests and Fungi, about how I’ve been inspired to look for other ways of photographing nature rather than simply taking traditional portrait shots. Rowleys Meadow which is on the edge of Histon, has mature ash trees (Fraxinus excelsior) on the periphery which are laden with ash keys and as a result there are thousands of young ash saplings:

Brown grass stems merge with the taller, thicker, silver stems of the ash saplings

And this presented a good opportunity to capture some abstract nature images. I like the way the low, bright sunlight creates a vertical pattern of silver and shadow as it illuminates hundreds of young ash trees

Back to birds, as well as our regular winter residents migrants from Scandinavia are much in evidence, redwing (Turdus iliacus, Dansk: vindrossel), and fieldfare (Turdus pilaris, Dansk: sjagger):

A lone fieldfare perched in a tree after gorging on a blackthorn bush laden with sloe berries

Small flocks of fieldfare can be seen and heard making there distinctive and diagnostic call, and the flocks will get bigger if the weather does turn wintry. Last winter, which was brutally cold here and in Scandinavia, huge numbers of waxwing (Bombycilla garrulus, Dansk: silkehale) arrived in the UK from Norway, but due to the much warmer weather I don’t think we’ll see them here in quite such abundance this year, which is a real shame because they are indeed spectacular:

Waxwing – it’s around the size of a starling and the colours are amazing

Histon has a resident rook colony (Corvus frugilegus, Dansk: sibirisk allike) who have their rookery in the tall trees adjacent to the church and are a constant source of aerial entertainment. They were feeding in a field along Guns Lane, which runs from Histon to Ely, as I wandered along it and this one took exception to my presence and flew over squawking at me as it went,

I took the hint and moved on, heading home. But a little further along Guns Lane I paused when I heard the quiet and delicate song of a flock of long tailed tits. So I stood still and they went about their routine in trees about 10m away. I really like these diminutive, gregarious, birds and I love trying to photograph them, which can be challenging as they are very small and they never settle in any one place for very long. But I managed to get this series of shots which I’m rather pleased with:

Even though the weather is pleasantly mild at the moment, I prefer winter when it’s cold, so I’m hoping it will start to behave as it should and these delightful little birds come back to feed in my garden!

5 Comments

Posted in Birds, Countryside walks, Garden birds, Ornithology, Walks around Cambridge and Histon

Tagged absence of garden birds, Aegithalos caudatus, ash, blackthorn, bogfinke, Bombycilla garrulus, Cambridge Science Park, Cambridgeshire, Carduelis carduelis, chaffinch, Corvus frugilegus, Countryfile, Fen Drayton Lakes, fieldfare, Fraxinus excelsior, Fringilla coelebs, goldfinch, grønspætte, great tit, green woodpecker, Guns Lane, halemejse, histon, long tailed tit, musvit, Parus major, Picus viridis, redwing, rook, Rowleys Meadow, RSPB, Scandinavian birds, sibirisk allike, silkehale, sjagger, sloe berries, stillits, thrushes, Turdus iliacus, Turdus pilaris, vindrossel, waxwing, winter migrants

The balance of nature

Posted on November 8, 2011 | 2 comments

At the end of May this year the BBC screened an episode of Countryfile in which John Craven interviewed a member of the scientific staff at the Game and Wildlife Conservation Trust (GWCT). Taking things literally I’d assumed the this was a trust who’s aim was the conservation of game and wildlife. However, as the interview progressed I began to question this assumption as the discussion centred around a study to be carried out by the GWCT in which magpies were to be eradicated from a specified test area to assess the local effect on songbird populations. I don’t think that removal of a native species such as the magpie by trapping and killing them is an ethical way to study predator/prey relationships. But is it scientific?

The magpie – villain of the piece – apparently

The interviewee from the GWCT, Dr Jeremy Stoate, justified the cull on scientific grounds suggesting that increased predator numbers result in significant reductions of prey populations and the species they identified as being largely responsible was the magpie.

Magpies are bold, brassy, ubiquitous, and are generally percieved as being a tad raffish. They undoubtedly predate songbird nests, but I struggled to understand how this could justify slaughtering them. Numerous other species of bird and mammal such as sparrowhawk, kestrel, owls, great spotted woodpeckers, rats, stoats and probably the biggest killer of small birds, domestic cats, all predate songbirds and some raid nests to poach eggs and chicks.

So why was it only magpies that were to be exterminated?

The action was being justified on a scientific basis, and whilst I’m no ecologist, I am a scientist, and the whole thing seemed unscientific, so I decided to do a little research of my own on the subject. Interestingly, since I did my initial research in June, it appears that references to the study on the GWCT website have been taken down. At least, I couldn’t find any.

However, what I did find out was that the study was commissioned and financed by another ‘conservation’ organisation called Songbird Survival. Whilst I believe that GWCT do have a genuine interest in the countryside as a whole, the same cannot be said for Songbird Survival. It is a registered UK charity whose statement of activities on UK Charity Commission website is this:

THE PRINCIPAL OBJECTIVE OF THE CHARITY IS TO IMPROVE, PROTECT AND PRESERVE FOR THE BENEFIT OF THE PUBLIC THE POPULATION OF SONG AND OTHER SMALL BIRDS BY THE CONSERVATION AND RECREATION OF HABITATS, BY SUITABLE EDUCATION OF THE PUBLIC AND LOBBYING MP’S AND THE HOUSE OF LORDS, TO EFFECT CHANGES IN THE LAW WHERE WE FEEL IT IS NECESSARY.

However, the details on the Charity Commission website also list the trustees, and that makes interesting reading too…

LORD COKE, MR CLIVE PATRICK SHERWOOD, MR FRED VALENTINE INGRAMS, MR JOHN RICHARD PUGH, LORD MICHAEL RICHARD RANKEILLOUR, MR ROBERT JOHN MIDDLEDITCH, MR DAVID GRIFFITH, MR NICK FORDE, LORD JOHN HADDINGTON, MR HUGH VAN CUTSEM, MR COLIN STRANG STEEL

All of these trustees are big landowners, or relatives of landowners, some with shooting estates, and they all support hunting and shooting. Lord Coke is the owner of Holkham Hall in Norfolk and he and several of his gamekeepers have been prosecuted for killing birds of prey by shooting and poisoning. So I’m struggling to believe that these people really have the best interests of songbirds at heart when they are funding ‘scientific’ destruction of a single predator species which has been implicated in taking gamebirds. And via the titled gentlemen listed as trustees they would be ideally placed to carry out their stated aim of ‘lobbying MP’s and the House of Lords‘.

Back to the science though. I recently attended a lecture in which Dr Mike Toms of the British Trust for Ornithology (BTO) talked about garden birds and how gardens are becoming an increasingly important sanctuary for increasing numbers of songbirds, and therefore predators, such as magpies, great spotted woodpeckers and sparrowhawks. In the course of his lecture Dr Toms talked about the decrease in songbird numbers and how magpies were being blamed but said that magpie predation was not the cause of the decline in numbers but habitat destruction and current agricultural practices were the primary reasons. I emailed Dr Toms and he was kind enough to send me several links to published work by the BTO into bird predation. This list included this publication: ‘Population changes of avian predators and grey squirrels in England: is there evidence for an impact on avian prey populations? Journal of Applied Ecology 47: 244- 252‘ describing a collaborative study between the BTO, GWCT and the University of St Andrews in which the impact of 2 groups of predators, those which predate adult birds and fledglings and those which predate nests (including the magpie) were analysed for 29 prey populations. Quoting directly from this paper:

‘For 22 avian prey species, there is no evidence that increases in common avian predators and grey squirrels are associated with large-scale depression of prey abundance or population declines‘.

Then:

‘Unexpected was a large number of positive (my italics) associations between predators and prey, particularly for native avian nest predators, which largely exonerates these predators as driving declines in passerine numbers‘

And:

‘Analyses of large-scale and extensive national monitoring data provide little underlying evidence for large-scale impacts of widespread avian predators and grey squirrels on avian prey populations…‘

The paper also describes negative correlations between the remaining seven prey species and predator numbers, and accepts that some of these may be causally related. Although e.g. the relationship between sparrowhawk and tree sparrow is probably significant, that between buzzard and goldfinch almost certainly isn’t. However, in an email from Dr Toms to me he indicates that the GWCT study showed negative causal relations on a local level but, crucially, not at a population level.

This last point is key to the argument. In a study of population dynamics, if conclusions are to be drawn about overall depletion of numbers in response to a specific influence small local studies cannot be extrapolated to enable conclusions for the population as a whole, and to do so is erroneous at best, misleading at worst.

Incidentally, I also found a publication on the website of Songbird Survival entitled ‘Detecting an impact of predation on bird populations depends on the methods used to assess the predators’, (Methods in Ecology and Evolution (2010),1,300-310, Nicoll M., Norris K.). This is an interesting paper because rather than analysing actual population data it investigates the methods used to analyse the data. And in the summary the last point recommends: ‘…the findings for studies which use opportunistic data, for a limited number of predator species, should be treated with caution and that future studies employ bespoke census techniques to monitor predator abundance for an appropriate suite of predators.’

This is interesting because it argues that the methods used to analyse opportunistic, observational data must be carefully optimised to ensure that conclusions drawn from the data adequately reflect the observations.

None of the publications suggest that slaughtering the predators is a rational scientific way to assess the negative impact on prey species. And I’m inclined to think that culling is poor science, particularly as the latest evidence suggests predator numbers don’t reflect negatively on songbird populations and in some instances there is actually a positive correlation between predator and prey, presumably because the predators remove the sick and the slow before they can add their DNA to the genepool.

I think the notion that predators destroy prey populations is bizarre because I was taught, and importantly, I believe it to be the case, that prey abundance determines predator numbers, not vice versa. If prey numbers decline then shortly afterwards so do predator numbers. Taking the reverse of this theory to it’s logical conclusion, if predator numbers determine prey numbers, all prey species would eventually become extinct and then the predators would also become extinct and the balance of nature which has prevailed for the last few billion years would be turned on its head. Which is absurd.

So population studies which are centred around the slaughter of predators seem to me to fly in the face of all current theory and are therefore morally indefensible aswell as being scientifically unsound, especially when commissioned and financed by such obvious vested interests as Songbird Survival.