Wednesday, 23 December 2015

Countdown

Dehesa sunset (Martin Kelsey)
Springtime weather in deep mid-winter, barely any rain for weeks but swathes of yellow crucifers in flower, a flavour of February indeed, coating the ground of the olive groves. In places even Gum Cistus has been bearing flowers, not to be expected until well into spring.  Tree frogs give their slow, measured grating croaks, unseasonally vocal. A confused and messed-up December it seems. The Barn Swallows I saw a week ago, hawking in the bands of sunshine across a placid pool are most likely to be overwintering birds: there are always a few lingerers right through winter, House Martins as well, and it will another four or five weeks until we start seeing genuine arrivals. A Yellow Wagtail we saw last week was a surprise, and most likely too an overwintering bird. But the adult Great Spotted Cuckoo seen this afternoon by a friend nearby must surely be an early migrant. It predates my first ever by ten days (and equals the earliest ever recorded). This is a species that leaves early (few remain beyond July) and has never been recorded here in the autumn.

And yet the recognisable features of December in Extremadura are plain to see and measurable by the milestones I have in place. The first of the winter crane counts took place last week and I spent the morning on my circuit: a slow-paced two hours meander through an astonishing diversity of habitats: stubble fields of rice and maize, wet muddy fields, winter wheat, dehesas, pastures, a reservoir and the edge of pseudosteppe. Each time I found flocks of Common Crane they were counted and their habitat noted. By the end of the morning I had seen over 4,300 birds. Their favoured stubble fields were also the haunts of parties of wintering Grey Lag Geese, one of which also had three Greater White-fronted Geese present as well, much rarer visitors here. Later that day, as the sun set through the near symmetrical architecture of the oaks in dehesa, I counted over 500 cranes flying into a roosting site, in three large bands, their bugling heralding their appearance over the tree-tops.


Two days later I am undertaking my routine twice-winter survey walk through the olives groves close to home. Rising fog impedes visibility slightly, but most of the birds are detected by sound. In two hours 635 encounters take place with a total of 34 species, with Blackcaps being by far the most numerous, 127 in total - wintering birds, attracted along with the Song Thrushes to the heavily ripe olives. Resident birds too like Hawfinches and Azure-winged Magpies feast on these high-energy fruits. A few weeks ago, whilst enjoying a picnic lunch nearby, we watched a large but loose group of Azure-winged Magpies, flying through the open dehesa with their characteristic undulating flight, defining shallow, long arcs and all in a single direction. These birds were truly driven by a purpose, for within five minutes, they reappeared, this time all heading in the diametrically opposite direction, and every one was carrying an olive in its bill, all returning from a group foray in the neighbouring olive field.

Azure-winged Magpies (John Hawkins)


Friday, 18 December 2015

Vulture nuptials

Adult Griffon Vulture (Martin Kelsey)
The Griffon Vultures were busy. As we stood before the vertical strata of quartzites at the Portilla del Tiétar in the magical Monfragüe National Park,  two dominant impressions started to pull on our senses. First the purposeful movement of Griffon Vultures, which was a striking contrast to their loafing behaviour as we arrived. Then the very border of the rockface was marked by hunched figures, perched vultures which, reptile-like, appeared to need to draw on the winter morning sun's insipid warmth. Slowly some spread their wings and tilted carefully to maximise their exposure to this energy. A few then rose, seemingly without effort, to rise in the fluid currents developing in the air, a medium of gradients and forces invisible to human perception. But most when taking off headed in a level, flapping flight to the hillside. This directed our attention there, andwe could see numbers of vultures dotted on the grassy slopes, hopping towards the wisps of retama bushes, whilst others had settled in the sturdy encina oaks.  There they tugged and grappled and minutes later, with the same detemined flight path in reverse, they approached the cliff with foliage-covered branches in their bills. Their legs dropped down, the flight braked and with amazing accuracy, perfected a landing precisely  on a small ledge where an untidy platform of twigs lay and their mate stood to guard.

The second sensual impression was an assault of sound, a wheezing, baying and moaning which echoed across the small gorge. Unlike the barrage of sound typical of seabird colonies, this could be pinpointed to specific locations. There one beheld the spectacle of vigorous copulation between these massive birds. The male perched on top of the female, their tails swivelled to ensure the meeting of cloacas, This was not the split-second flurry typical of most birds. It was a heaving noisy union which lasted impressively close to a minute.

Mid-December and the breeding season of the Griffon Vultures was already underway. Indeed as we scanned the gorgeous architecture of these ancient rocks, we found at least one pair of birds where whilst one stood the other was sitting tight on the nest, apparently already incubating their single egg. My friend, Ángel Sanchez, who is a senior conservationist in the government of Extremadura, as well as being an excellent ecologist and naturalist, has described the fascinating ecological differences that drive the different breeding cycles of our two largest carrion feeders: the Griffon and Black Vultures. Griffon Vultures feed on the carcases of large herbivores, be they wild (deer or boar) or livestock such as sheep or cattle. For these species the mortality rates are highest in late summer to early winter. Black Vultures, on the other hand, nesting in trees and colonial in only a very loose way, and tending to be more solitary by nature, evolved to feed on smaller prey, especially rabbits. On a visit this week to the Lacañada Hide where animal remains had been laid out to lure-in vultures, it was the Griffons which poured in like a frenzied scrum to disintegrate a whole carcase in minutes, whilst the Black Vultures moved in to feed on the scattered remains and morsels that the Griffon Vultures had disregarded.
Black and Griffon Vultures (Martin Kelsey)
Rabbit mortality is higher in the spring, thus Black Vulture breeding activity occurs much later than that of the their cousins. Human activity is changing this relationship as the vulture species benefit from both the increased number of livestock grazing on the vast tracks of Extrenadura's pseudosteppes and dehesas and the intensification of large hunting estates, where it is estimated that during autumn and winter a thousand tonnes of animal remains from deer and boar are consumed by vultures, more than a third of their annual requirement. This, Ángel says, is underwriting the needs of the Griffon Vultures at the onset of their breeding and substituting for the diminishing rabbit populations for the Black Vultures. Hence the remarkable increase in the population sizes of both species, especially dramatic in the case of Black Vultures which in forty years have increased from about 90 to over 900 pairs in Extremadura, with concentrations in the Monfragüe region and the Sierra de San Pedro.