Wednesday 27 March 2013

Topsham Harriers - not a football team...

Topsham Recreation Ground - 10th March 2013

I popped down to the River Exe at Topsham Recreation Ground on midday Sunday for some fresh air, exercise and a quick look at the low tide gulls. A few minutes later the dog was wondering which stone she would carry home today (no, I don’t know why), I was trying to turn a large darkish Herring Gull with an interesting primary pattern into an argentatus when everything got up and flew off. Typically this means a raptor in the vicinity. Sometimes it’s a hunting Peregrine but can often be just a distant Sparrowhawk – not really much threat to a large gull – but today it was a harrier quartering the reed bed across the river.

I’d found a Marsh Harrier here two days before and only managed distant shots so, thinking I might get something better today, I started shooting away with my Nikon in burst mode. The I noticed the bright white rump – excellent, now I’ve got a Hen Harrier. At that point, with the bird flying ever closer, the camera battery died. I had a spare, quickly changed it and looked up expecting to see a tiny speck disappearing across the river. But it was still there, floating at near stalling speed over the reeds. After a few more shots I realised I was photographing a Marsh Harrier after all and I began to wonder if I’d hallucinated the white-rump.

Photographic evidence was conclusive and I’m relieved to report that my faculties are not yet that damaged. In hundreds of hours at this site over 13 years I’ve seen exactly one Marsh and one Hen Harrier (and the last was on the Exminster side). Now I get one of each within a minute, and perhaps, but for a battery, I might have got them in the same frame. Now I wondered if harriers are like buses, wait for ages and then three turn up together. I hung around awhile confidently expecting a Pallid Harrier but no luck.

I like to try to get maximum value from photos so I thought it would be fun to see if it was possible to decide the age and sex of each bird. First the Marsh Harrier (all ID criteria based on Forsman, 1999).

From my previous distant views and photos it was quite clear that the Marsh harrier was a male. Easy enough, the distinctly blackish outer primaries contrasting sharply with the paler greyish inner primaries and secondaries are diagnostic of males. The broad darker trailing edge to the wing, visible on both surfaces, is not an adult feature so this is a young bird. A bird in it’s second year should, in March, still be carrying it’s juvenile flight feathers, uniform in colour but now quite worn and faded. So what about an older bird? In March a third year should have moulted it’s wing feathers to a more adult-like set, which is what this bird seems to show. Another indication is the large amount of black on the outer primaries, an adult would typically show rather less than this.

And the Hen Harrier? That’s a bit trickier and the choice here is between adult (or adult type) female or second spring immature; it’s obviously not an older male as even a third year bird would look basically pale grey with black wing tips. Juveniles have narrower and more pointed wings than adults but I really don’t see Hen Harriers regularly enough to feel confident about judging this. However, there should be some plumages features which would help to age it. Juvenile Hen Harriers appear to moult few feathers (and certainly no flight feathers) until their first complete moult starting in late spring of their second year. Adults have a complete moult finishing in September-October. So, in March, a first spring bird should look quite worn and faded compared to a much fresher plumaged adult. I don’t think this bird looks particularly worn or faded, there are obvious pale tips to the secondaries, inner primaries and tail feathers and probably also the upper greater coverts,  indicating third year at least. One thing bothers me though, on some of the photos the secondaries seem quite a bit darker than the primaries which is a juvenile feature.

So which is it? Well, to be honest, I’m not sure. I think I’ll have to put this one down as probably an adult female. On the other hand, there’s always the chance it’s still around and I can get better photos.

Forsman, D. (1999) The Raptors of Europe and The Middle East. Poyser, London.

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