Curlews- the long and the short of it

As you've probably noticed, I'm no photographer. Record pics only. If I get a hundred metres from the house before realising I've left my camera behind, I carry on regardless, I'm out to bird. I do sometimes regret it.

The other morning I was cursing at the Curlews for catching me out. Some had clearly just changed behaviour. In the hour after dawn, small groups were coming off of the roost fields around Ham Green and flying low, to the south and inland, over Windmill Hill.

I'm no scientist... so my mind immediately went 'migration?' Mid-winter readjustment, birds moving south? Couldn't be. Most studies have shown this species migrates directly and quickly between breeding grounds and wintering sites. They don't re-adjust. It took me a minute or three to recall the actual behaviour I was seeing.

Some Curlew change their feeding behaviour as the winter progresses. For a few weeks now, bang on time, further east along the estuary more and more Curlews had been found feeding routinely on the fields of Raspberry Hill. Their main prey in the mudflats, ragworms, are a lot harder to find around now, and earthworms become more important in their diet.

It is not because the estuary food is running out. Yes, the ragworms are somewhat depleted, but they become harder to locate as they bury themselves deeper in the mud in colder weather. In very rough terms, the longer-billed females can still find enough out on the mud, but shorter-billed males find the going tougher and it is mainly these males that switch to the fields.

So, there should a drop in numbers feeding out on the mudflats during the low tide cycle in mid-winter as birds head for the fields in daylight hours. And there is, with peaks of 'inland feeding coming during late December. Easy to see around Raspberry Hill, grassy fields are close-by the flats. Travel west, between Upchurch and Lower Halstow, and flocks are often encountered around Green Farm and Holywell Farm. But on the inner estuary, where exactly do commuting Curlews go? And as more fields are lost, can males cope? Just how far are they prepared to fly inland to feed before the Medway begins to look unattractive as a wintering site?

Ortstreue. Another of those lovely German ornithological terms that you stumble upon in textbooks as you try to find answers to such questions. 'Ort' + 'streue' =  'Place' + 'scatter'. "Winter ortstreue of Curlews is probably strong", says volume III of 'The Birds of the Western Palearctic'. Fidelity to a territory, at both ends of the migration route- Curlews stick to a home territory and a winter territory. Makes sense, why many Curlews do not feed as a flock but claim a wintering territory on the flats and then defend it against others. A wintering short-billed bird, that has found both mudflat and grassland in one winter, will probably head straight back for that area the next year.

The day after I'd failed to get the pic was Boxing Day. Out the front door 20 minutes before sun up, no commuter traffic noise, the Medway Towns were sleeping. Turning into Otterham Quay Lane, first birds heard? Curlew, south. Lost the cries towards Meresborough, probably went beyond. (And, yup, the camera card had been back in my PC.)

How much surrounding development can an estuary take before short-billeds find the going too tough? The texts hint at a maximum distance Curlews seem willing to try being around 15 miles.

Tonight I got the chance to watch that Windmill Hill flightline back. They came back in one large group about ten minutes after sunset, quiet, fast, and low, dropping into Otterham Creek on the flats near the sewage farm. (And, yup, I'd already put my camera away. Civil twilight and all that.)

I really am no photographer, but I do want a shot of the behaviour locally now. For this blogpost I've had to make do with a snap from three winters ago, when these Otterham Curlews could still be lazy and fly all of a hundred metres onto Motney, back when the grass was short, back when I'd never knowingly picked up on a mid-winter commuter route over Windmill Hill.

Motney Hill, December 2013