Saturday, 9 November 2013

Thick-knees at roost

Stone Curlew (David Palmer)
Despite being widespread on the open plains, Stone Curlews (or Eurasian Thick-knees, as they are sometimes called) can be tricky to find in the spring. This is partly because of their wonderfully cryptic plumage and their preference for bare open ground, which on a sunny day will be bathed in heat haze by mid-morning, meaning that ground-dwelling birds will, as it were, dissolve in the shimmer. It is not helped also by the fact that Stone Curlews are mainly nocturnal, so one will be looking for birds at their most inactive period of the day: standing motionless or, worse still, sitting down flat on the ground. In autumn and winter, on the other hand, the task is much easier, and this is because, like many birds outside the breeding season, the Stone Curlew forms winter communal roosts. So with little heat haze to worry about, once one has found the roost, one should be able to enjoy prolonged views of often rather sleepy thick-knees. The roost sites tend to be traditional, a cultural transmission down through the years and across generations of Stone Curlews. What is interesting is how often these sites persist as chosen roosting areas, even though some of the features which might have made them attractive have disappeared. One roost which I first became acquainted with about eight years ago, had all the appearance of a classic site with large pebbly patches on the ground, wheat stubble and some widely spaces trees at the edge. The field then became converted to a solar farm, with huge solar panels covering the terrain. This was too much for the Stone Curlews. But instead of moving off to a less-disturbed area, they merely moved barely a hundred metres. This roost is now in rough pasture, in a rather impoverished-looking tree-plantation, beside a busy (for local standards) main road and next to derelict buildings used by local youngsters for mini-raves on a Saturday night. Weekends will also witness greyhounds being exercised there. It is hard to imagine a less attractive place for Stone Curlews. Indeed at first glance, it is easy to assume that your misgivings are well-founded as the first one is often quite hard to spot. Suddenly though something catches your eye, a hunched shape, with striking yellow legs and half-closed, rather dozy, yellow eyes, as depicted beautifully in David Palmer's photo above taken at this particular roost.

Once you have seen one, nearby shapes also metamorphose into Stone Curlews, some sitting on the ground, others like the first standing hunch-backed, a few taking a few paces walk. Ten birds..twelve...fifteen.. in view. But it takes a passing danger, perhaps a Marsh Harrier drifting overhead to get a true estimate of the numbers there. Seventy or eighty take flight, descending soon afterwards on a glide with their rather long gull-like wings.

I often wonder where they all come from. I know of two other roosts of similar size not more than a few kilometres away. Together the number of wintering Stone Curlew in these three roosts must exceed the breeding population within a similar radius. We do know that birds from northern Spain move further south in the winter and the Spanish population is supplemented by wintering birds from places like France and England. But until a bird turns up bearing a coloured-ring, I will only be able to guess the origin of them at this roost, although I can more safely assume that this communal roost will comprise the same birds from one year to the next, showing a site faithfulness or philopatry, which offers survival advantages drawn from familiarity with a particular area, its resources and risks.

On last Friday evening I was in Trujillo, undertaking parental duties waiting to collect our teenage son Patrick from a classmate's birthday party. As I sat in the car, I could hear the continuous sound of Spotless Starlings, still making a racket a couple of hours after nightfall from their communal roost site in a stand of trees in a town park. After a day feeding out on the plains, hundreds upon hundreds arrive at dusk. One theory about the function of such communal roosts is that they offer means for hungry starlings to obtain information about the best local food sources, presumably they follow well-fed birds out to the pastures the following morning hoping that they will be led to the right places.  And I could only imagine the type of communication going on between these garrulous birds, well past their bed-time. In fact so much noise was coming from the roost that it took me a few minutes to register a different sound altogether. Trying to block out the starlings I could now recognise the unmistakeable sonorous deep hoot of an Eagle Owl. I walked along the street in the direction of the sound, looking upwards.  And there, perched on top of a tower, seemingly oblivious to the sight and sound of traffic and people was the Eagle Owl, the street lamps catching, as it turned its face, its caramel-coloured eyes. I could even see the pale bases of the throat feathers each time it hooted. It sat there for half an hour, calling two or three times a minute, before silently gliding off on its broad wings to hunt. The nocturnal predator was on the move over the rooftops, as the diurnal starlings at last settled down in their roost.

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