Our winter wildfowl numbers at Paxton Pits can be absolutely amazing, or they can be really disappointing, despite conditions being more or less the same here, year on year. After visiting the Welney Washes on Saturday (see my photos) I had the following thoughts:
There are global factors that influence the numbers of migrating wildfowl in the UK and local conditions influence bird movements within the UK. So, if the Washes hold loads of widgeon, Bewick swans or pochards, then why don't we? The answer is that, if these very mobile birds come to the UK, they seek the very best feeding sites at that particular time. In mild winters, many ducks congregate in Denmark and Holland and just don't bother to hop the North Sea. That's why we have not seen many smew or other diving ducks this year. However, the bigger wildfowl such as swans and geese are pretty traditional about where they go because the parents teach the youngsters the routes.
Not all ducks eat the same food and so a site that provides a lot of grain may attract many pochards and mallards, but less gadwall and goldeneyes. The Washes are seasonally flooded pastures, so they provide a lot of invertebrates and seeds from the fields, but almost no fish. The pits at Paxton Pits are always full of water so a proper freshwater ecosystem has built up with stable water levels and a good variety of natural foods. Goosanders are attracted to us because we have lots of fish in the lakes, and the river. Water levels play a crucial part in determining where wildfowl will feed. If Icelandic widgeon arrive before the Washes flood, many of them come to Paxton first. If the Washes are flooded too deep, then dabbling ducks can't reach the bottom and so they leave while the diving duck numbers increase.
It's not all about feeding either. Water birds like to roost and loaf about on dry land so, if a flood covers all of their fox-free sand-bars and islands they will leave, even if there is plenty of food. They can be driven off by disturbance too.
This week we are experiencing a drop in temperatures that may herald the first big freeze-up of the year. If our ponds freeze for several days some birds will move to the river which should not freeze, others may leave the UK altogether. Kingfishers can't feed through the ice and if the river is swollen and murky they can't feed there either.
Sadly, a few days of freezing weather can seriously deplete the numbers of our resident goldcrests, long-tailed tits and wrens, all of which are plentiful at present.
