With thanks to volunteer Phil for his article and photos.
Five years ago I wrote an article for the blog entitled “When the water freezes”. This followed a spectacular early morning at the reserve doing the monthly Wetland Bird Survey (WeBS) following a clear and very frosty January night. The article can be found at this link.
When the water freezes... - Pulborough Brooks - Pulborough Brooks - The RSPB Community
I was reminded of this a few weeks ago at the start of what proved to be a very cold and frosty few days before more winter storms brought much milder air and very strong winds.
The 15 January WeBS followed another frosty night and I had expected to see, as per 5 years ago, many ducks on the River Arun escaping the frozen water on the Brooks. However, it turned out I wasn’t right. The overnight temperature may not have been below zero for so long so there were still many patches of open water as well as some that had duly frozen.
Determined to make it to the riverbank to check for birds on the Arun, the South Brooks WeBS team split and myself and a colleague had a bit of an adventure to reach the riverbank. We just about managed to pick our way through the floods to the top of the bank.
It soon became clear that the ice was not so extensive as expected and that many of the ducks, which might otherwise have gone on the river, were in fact still occupying open water on the Brooks. We had a relatively easy time counting the few birds coming off the river; just a few Mallard and Teal. We also disturbed several Snipe, many more in fact than the other team members achieved from their vantage point.
As with 5 years ago there were some lovely views to enjoy. Here for example is a view of the flooded brooks looking back towards the Wetland Trail at West Mead – not something many people are able to see.
And on the return walk we couldn’t help noticing 2 White-tailed Eagles perched in a prominent tree that I usually find myself checking out from further away at Winpenny Hide.
Meeting up eventually with the rest of the team we discovered they had experienced a less adventurous walk but a much harder task of counting with several hundred birds to survey.
By the time I returned on Friday 19 for ‘Hides and Trails’ duty there had been several much colder nights and the only clear water available was in a few spots where a huddle of ducks had managed to stop the water freezing. On the North Brooks it seemed this clear water was all in a line going from right to left as seen here from Jupp’s View.
Before this I had spent some time in West Mead and Winpenny Hides observing another effect of the freezing water; the Snipe find it much easier to probe into the grassy areas than into the mud on the pool margins which had all frozen. This means that they can be much easier to spot. I surmised that the grass inhibits the frost from penetrating so far into the ground and the sun warms it up more quickly to a temperature where Snipe can feed successfully with their long bills. There were at least 6 Snipe feeding very openly on grass in front of West Mead Hide and a similar number at Winpenny.
Later on Friday I paid another visit to West Mead to see the sunset and there spotted a Snipe now probing into a non-frozen wet patch near the hide and beautifully lit by the low sun.
It seems that Snipe will always prefer to feed in very wet or muddy ground.
Whilst in the 2 hides I noticed a large flock of Teal coming up from the river. They had probably been disturbed by a raptor and this could possibly have been one of the eagles which I noticed perched again in the same tree. A Marsh Harrier also flew downstream on one occasion and may also have been a culprit.
Another interesting thing I realised is that not all our wintering duck species will move onto the river. As per 5 years ago there were certainly Teal and most probably Wigeon and Mallard there, but I have never seen Shovelers or Pintails on the river and it seems that for some reason these species do not feel comfortable there. I have not yet been able to discover why although I have read recently that Pintails tend to prefer larger bodies of open water so would find the river rather restricting. This would certainly explain why we have tended to see more Pintails in big flood conditions. After the autumn rain there were over 400 on the reserve at the time of the December WeBS. Note that several Shovelers and Pintails can be seen in the North Brooks clear water photo above.
I spent some time in Winpenny Hide trying to spot a Water Rail driven out into the open by the freezing water but had no luck despite it being spotted by many other people during the day. I also drew a blank on Water Rail at Nettley’s Hide where I had glimpsed one the previous week being its usual secretive self in less cold conditions.
While at Nettley’s I noticed another effect of the ice. Perhaps 90% of the water surface was frozen but underneath the ice layer the floodwater was still dropping as it ran out through the sluice gates into the river. So the ditch outside Nettley's Hide was not only frozen but it also had a cracked sloping margin which some time earlier had been flat on the surface of the flood.
This reminded me of a day of similar conditions in January last year when every now and again there would be a loud crack as the ice dropped to fill the void underneath left by the receding water.
The freezing weather is of course not so good for the wildlife but it will find ways of coping. As for me I am already feeling rather nostalgic about those very cold sunlit days of last week when everything sparkles and it feels good to be out in such a beautiful place.