Friday, 28 January 2011

Birding by weight....

A truly spectacular afternoon on the Dee Estuary. On an afternoon like the one I've just had it rivals anyplace I've ever been for wildlife watching home or abroad. The pendulum had swung back to clear and blue and the flats shone with a shine that couldn't be rubbed off if you tried.

There was soooooo much about. I don't usually count stuff when I'm out, I just like looking and watching behaviour, but today I had a go. It occurred to me that we define so much about birds on estuaries with numbers. So much so that I sometimes feel that these figures lose a little of their meaning. How else could I describe the vast amount of birdlife in front of me? What about weight?
That was it, I'd count everthing I could see from the beach and work out the aggregate weight of each species to give a different perspective on the Dee's avifauna. So, eye to scope and notebook in hand I was off....

(A little note: I have made a few assumptions with a couple of species. Firstly, where weights differ for male and female I have taken an average of the two values. eg for Pintail males are on average 900g and females 700g, so I have done my maths using 800g. This also assumes that there is a 50-50 split between males and females. This is not always the case, but I thought I'd keep it simple and believe there is today!)

First thing I notice is that there is a lot of Knot. Like a lot a lot. It takes a while but I get a rough figure. I end up spending three full hours on the beach and as the tide starts to dribble in more come in from Caldy. I end up with a huge total. There are big groups roosting in the channel, too far for the conventional camera so I jam the mobile up against the scope for an improvised view, but you get the idea....
If each of the Knot I counted today weighs 140g ( I got the weight values for the birds from the BTO website) then by 4.15pm as the sun was setting I had seen an astonishing 2.52 metric tons of Red Knot!

1.1kg's of female Peregrine Falcon whizzed low over the beach from the cliff top and put at least a ton up, the noise drowning out the 737 coming in to land at Liverpool airport, seriously, it was the stuff of wildlife documentary legends!

The Knot wern't alone, in the channel were 130.2 kg of Black-tailed Godwits including colour-ringed bird YN-RX. This has been seen on the estuary before, but not be me so I was rather chuffed that I connected with all 310g of it.

Diminutive Dunlin were present in big numbers. I estimate that there was 192 kg of them. These birds only weigh in at a tiny 48g apiece and even though they outnumbered the Blackwits by 10:1 they were only 60kg heavier!

Scanning around I settle on a different wader. 240g of Grey Plover is wandering all on its own close to the channel. This makes it the lightest species recorded today!

Just over the channel are 165kg of Curlew. Behind them there are 370.7kg of roosting Shelduck.
They are loafing in small groups on the mudflats, heads under wings. As there is a high pressure and absolutely no wind the tide seeps in around them so slowly that some barely raise an eyelid as they float up and off towards the marsh.

The Pintail, all 248.8kg of them, are a little more animated as the tide approaches. They hoot to each other and join up into little flotillas to drift marsh-wards. The males resplendant in silhouette as the sun sinks towards the Welsh hills. The tide continues to push the birds around and the sights and sounds of so many birds is breathtaking. I don't want the show to end, but it finishes with a glorious sunset and I can return home to dig out the calculator....

1 comment:

  1. LOVE IT!!! A man after my own heart - inspired stuff young fella m'lad :D

    Those knot weighed more than my battered old volvo... BUT I bet they took up a greater volume ;)