Tuesday, 5 May 2015

Counting Birds

Garden Warbler
by Phil Smith.
Our annual breeding bird survey season was supposed to start last Sunday but the weather was predicted to be dire and so we moved the count to the Bank Holiday Monday morning at 6:45. It was definitely a good decision.

The Survey consists of two counts, one on the first Sunday in May and the second a month later in June. The theory is that, by putting in the same amount of effort on the same dates each year, we can compare results from year to year and make some assumptions regarding the rise and decline of various species. However, there's always the English spring weather to throw in some randomicity! If both visits have bad weather many, if not most, birds will be missed and the exercise will be pointless.

Good weather definitely gives us a better chance of counting most of the breeding activity going on, and so it proved on Monday.

Willow Warbler
by Phil Smith.
I arrived early beneath a clear blue sky and heard a nightingale as soon as I opened the door of my car. The territory in the Fishermen's Car Park is occupied again. Every year a willow warbler sings from the power cable there and a lesser whitethroat nests on the mound. All of those birds were back and all singing. Meanwhile a silent pair of bullfinches fed on the ground. There was a cuckoo calling across the meadow and garden warblers all around. This was going to be a good count without any doubt.

The day's counters assembled in our car park where Ray Matthews handed us our maps and paired novices with old lags. Some people's routes are much longer than others because we try to cover the entire site, including the A1 pits and the new workings. The total area is about three miles long by half a mile wide.

Ann Scott and I work on the Meadow Trail together because I am losing my hearing and hers is amazing. I have to tell her to only call out the birds that she can hear that are actually in Cambridgeshire! I can hear the loud birds with relatively low pitched voices, so I have the Canada geese covered but not the grasshopper warblers and gold crests. Fortunately I have excellent long sight and can still pick up distant birds while they are tiny specks in the sky. Unfortunately, that's not much use for a breeding bird survey where you are only interested in those birds that are nesting and not those that are migrating over.

by Phil Smith.
After two hours in the field, my map was thick with pencil marks that indicated every bird that we saw or heard and what it was doing. I'm sure the other counters had similar results with birds packed tightly in all the scrubby, woody, rushy and reedy patches and more sparsely in open areas.

Our chances of getting a really accurate picture of breeding activity are definitely increased if the weather is good, but it would also help if we could increase the number of visits. This year, we are supplementing the two Breeding Bird Surveys (BBS) with two more Sunday sessions that aim to get a handle on the real number of nightingales that are singing on the entire site. Last year's total of 24 came from just the two BBS counts so I believe there were probably a few more than that.

The full results will not be available for quite a while, but early observations suggest that our resident small birds like dunnocks, robins, wrens and tits had a good winter because we heard loads of them. Ray tells me that the number of nightingales recorded was 14 and I'm sure we will find more.

Drainage men.
Ray Matthews and Matt Hall return from Pumphouse Pit,
 by way of the Amazon Jungle?
If you regularly watch the birds on the Sailing Lake you will have noticed that there are almost no terns or gulls there. Usually they make a huge din all day ling that can be heard from the visitors'  centre. Have  they been scared off? Has the habitat become unsuitable?

The answer is that they have moved to Pumphouse Pit which is deep within the quarry where visitors are not allowed. These birds like to nest in tight colonies for defence purposes and so they either all move or they all stay. The wardens of RSPB reserves know all too well that you can spend a lot of time and money maintaining suitable safe places for terns to nest only to find that they prefer the car park!

The move to Pumphouse Pit is no accident. That lake was designed to have a host of islands of different sizes to allow gulls, terns and waders to sort out their turf. After the gravel company moth-balled the site the area flooded and it has taken a huge amount of work to create new drains that allow us to get the water levels back down to as near the river-level as possible. This year, we achieved it and all of the islands are exposed and occupied. We hope that the population will grow to the point that all of our islands are used every year.

In any population there are always a few pioneers or loaners who go their own way, for whatever reason. Amongst our terns there a few conservatives who might have found the move to Pumphouse too much to take. They were possibly hatched on the Sailing Lake or they reared young there last year and so think of it as a safe bet, maybe even as home. Another completely different theory is that the loaners are first time nesters who were pushed out to the edges of the new colony and gave up trying to fight their way in.
This year's lodgers. Photo by Phil Smith.

What about the terns on our rafts in Heronry North? My theory is that the first pair to arrive were the ones that bred there last year. They waited around on the mooring buoy until we launched the platforms and immediately settled in to nest on the older of the two rafts. My theory us that they were hatched on a similar platform somewhere else and therefore prefer rafts to islands.