大象传媒

The Winter that Would not Stop 2

• Julian Hector
• 17 Jul 06, 02:03 PM

If the Gulf stream is changing then of course I think we all know the implications for that, and I look forward to studying Snowy Owls in South West England, but how long given current speed of changes do I need to wait to at least see them in the winter? UK owl conservationist and PEuT reporter Chris Sperring has sent this blog to you. Owls could be an important indicator of climate change - these are his questions - And read on: (Chris sending down some pics, so come back!)

1) How far reaching was the cold winter of 2005/6, was it the whole of the northern hemisphere, or just part?

2) How much did our (UK) cold winter have to do with a weakening of the gulf stream from the south west, thus allowing air flow from the east to be dominant (do we know)?

3) Or was this a one off to be repeated once in every few years?

As I'm sat here on what feels like the hottest day this year I'm reminded just how cold and for so long the winter 2005/6 really was.

Certainly Tawny owls had been affected during this last winter, as I had never had so many adults brought to me as casualties or indeed brought to my attention as a public call out. Three of the Tawny owls had been observed by members of the public feeding in the day on their garden lawns. These three were so weak they were easy to catch, and indeed had classic signs around the outside of the beck area that they had been trying to feed by grubbing into the soil. All these casualties brought to my attention showed classic problems associated with low condition and weight.

But the problems of the winter persisted through to what should have been pre-breeding behaviour for the Tawny owl (Feb-March), indeed productivity of Tawny owlet here in my study areas was low to non existent.

For the 2005 breeding season in Goblin Combe woodland, which is a 200 acre deciduous mixed conifer wood in North Somerset, the 6 pairs of Tawny owl that operate in and around the woodland had 14 owlets, however for this year the number of owlets produced is 0, yes that's zero. Indeed this made me search other woodlands that I knew should have good numbers of owlets, the total count of woodland visited is 30 the number of potential owlets that could be produced would be or could be 100, the number found was 5 with ease, others could have been around but I basically kept to the same methods of detection I have kept to for many years.

This level of productivity if repeated in a wider area say all over UK would have a tremendous knock on-effect to the adult population, because if of course we then bring adult mortality into the equation, with low numbers of owlets produced and adults just dying as adults do (naturally) the population level must then be off balanced, so we would see if repeated in a wider area, rapid decline.

Barn owls as adults appear to have faired better through the winter, or so it seems. However this winter has a big sting in the tail for them as well. With the fact that the winter was long, cold and dry seems to be why barn owl has faired better, and that is has simply adjusted to hunting day time as well night. If however the winter had been wet or long periods of with long periods of snow, then the barn owl would have also been badly affected with high adult mortality.

But now here is the sting in the tail. With the long winter came suppressed grass growth in the spring, and indeed the late spring meant production of fresh shoots of grass so vital for the Short-tailed vole (favoured prey item in South-West England of the Barn owl) was late growing, this then knocked on to the Vole population which responded to this by very late breeding.

So in fact what we see happening now is that last year in early July 2005, I had finished my barn owl nest monitoring, with many of the barn owlets on the wing and fledged, but this year 2006, a lot of the nest sites look like that they are almost 10 weeks behind time, with some pairs even now just beginning their breeding season, and this appears to be happening everywhere within my study area of Somerset and Avon.

The additional sting for the barn owl is that of course as they begin the catch up and lay eggs now (July), the timing for the season could not be worse, in that their egg laying will clash with the normal hay and silage cuts, and this will cause failures of these broods in some areas, meaning again low owlet productivity.

Some people are already saying that its just a bad year for Voles. OK this is fine but explain it, as Voles or Mice all over the UK don't just all decide this is bad year lets crash, it must be cause and affect, indeed I have studied this in Voles for many years and I can have one field which shows a massive vole population compared to the next field which show a collapsing population the reason for this is grass growth and the time allowed for the density of grass to build up. So for them all to have a bad year at the same time must be something else governing this and that something must be the weather!

Two weeks ago I was in Cumbria meeting my old friend Tony Warburton, he lives on the south coast of Cornwall, and he wanted me to explain why they had no Short Tailed Voles, turning up in their normal rough grassland areas.

When it came to talking weather during the last winter he explained that they had frost lasting day and night and lasting for long periods so the same as in South-West England, except as Tony said," they just don't normally get frosts in there area of Cumbria as it faces straight into the south west flow from the gulf air stream".

May I now change tack and talk humans, because was it my imagination or did I not hear on the news that China and Japan had record low winter temperatures, and that people were dying because of this.

A friend that works in Germany and Holland also brought home talk of severe cold.

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