A Counting Time

I seem to have been out counting birds a lot in the last few days. On Friday morning I was on the shore of Portsmouth Harbour near the Roman fort of Portchester Castle watching a flock of brent geese. Unfortunately they did not do very much, although this did not mean it was a waste of time. This particular flock of over 500 birds included just seven juveniles, two pairs with a single gosling each, one pair with two and one pair with three. This illustrates that although lots of geese may go up to Siberia to nest, quiet often very few actually rear any young. Long term studies have shown that many birds, even though they may live a good few years, will never produce any young, whilst others will produce broods year after year. The important part of any population is that section that contributes to the next generation, this is the effective population, so knowing which birds these are and where they prefer to be, is important in developing a conservation strategy. The birds I was watching were feeding on sea lettuce, a kind of bright green seaweed that grows on the mudflats.


Brent geese near Portchester Castle

Brent geese, in common with a number of other Arctic nesting geese and swans migrate as a family and will stay together all winter, allowing the juveniles to learn where the best feeding areas are. From studies of ringed birds we know that birds will come back year after year to exactly the same feeding areas as they did with their parents in their first winter. So staying with your family is important and family members can be seen and heard calling to one another whenever they are on the move so that they don’t get lost in the mass of birds.


A brent goose family. Dad is on the lookout and the youngsters are behind, you can tell them by the pale bars across the closed wings.

If you look at brent geese feeding on grass you will generally find a far higher proportion of juveniles than you will see in flocks feeding on intertidal areas. Feeding on grass allows them to feed more continuously and to get more food and, of course, the tide does not come in and cover your dinner. For this reason grassland feeding areas are particularly important for the effective population. What all this means is that just counting the birds to find out where the largest numbers are does not necessarily tell you were the most important sites are, for a successful conservation strategy you need to go into things in a bit more detail.

Today we were counting wildfowl at Blashford Lakes, this should have been done last Wednesday, but fog intervened and almost no birds could be seen! Today I arrived at first light to find things not much better, but luckily the mist cleared and a count was possible in the end. The ducks at Blashford do not stay together as families, so I have no idea if they birds I count are champion breeders and major contributors to the next generation of biological dead-ends, probably some of both. So we just count the number of birds on each lake, this gives an indication of the relative importance of each lake and allows us to see trends in numbers.

Blashford Lakes is internationally important for the number of gadwall that winter here, this accolade goes to any site that regularly holds 1% or more of the west European population. Today’s count of gadwall, at a total of 762, was comfortably above this threshold. It was notable that most of them were on just two of the lakes, which shows how conditions can vary even between lakes that are beside one another.

The highlight of the day was at the end when locking up I saw two bittern from Ivy North hide, one sitting up high in the reeds to the left of the hide and the other out in the open under the trees to the right. Standing up high in the reeds is something they seem to do quite often, they can even walk along, gathering bunches of reeds using their neck until bunched enough to be grabbed in their large feet. In this way by alternately sweeping one way and then the other they can proceed at some speed a meter or more above the water. I got this shot of one standing up in the reeds at dusk on Friday evening, when I visited the hide on a walk with our volunteers.


Bittern standing up in the reeds