Girton Birdwatch - September 2009
I wonder how many readers of this column have seen a Golden Oriole in this country? I would guess not many. I certainly haven't, although apparently there was one on the Isles of Scilly when we were there in June, but I 'dipped'. I have seen them in various regions of southern France and once in Mallorca, but Britain? No. So what, you might ask? Well, there are two reasons, at least on the face of it, for surprise. The first is that the male Golden Oriole is arguably one of our most brilliantly coloured and stunningly beautiful summer visitors; the second is that if one can't find the bird in this region then the chances of seeing it at all are extremely slim, for not only is it an annual visitor to the East Anglian fens, but in most years the fenland colony provides the only British breeding records.
Neither is the Golden Oriole a small bird, being 24cm (9.5in) long, which is only a little shorter than a Green Woodpecker; indeed, the greenish yellow female, with its undulating flight, can be easily confused with this woodpecker. (Cocker and Mabey suggest that the existence of an old Somerset name for Green Woodpecker, 'woodwall', raises an intriguing possibility and harkens back to a time when the Oriole was a much more common British bird. It is thought to derive from wodewale, a medieval word for Golden Oriole, of whose song it is closely onomatopoeic). The male Oriole is a beautiful bright yellow, with mainly black wings and tail. Catch a glimpse of it in the open and you can't believe that you experienced such difficulty seeing it amongst the trees, even when you knew it was there. And you will know because the male, in the breeding season, possesses a rather melancholy but fast and clear fluting whistle, 'choo-klee-klooee'. Another indication that the bird is present is its cat-like contact squawk or alarm call.
However, this is a strictly arboreal bird which prefers the canopy of predominantly deciduous trees in well-wooded areas; it is particularly fond of poplars. If you can imagine a stand of poplars in spring or early summer, especially with a light breeze ruffling their leaves, then it becomes easier to understand why it's so difficult to spot this buttercup-yellow and jet-black bird as it slips through the shifting mosaic of sun, shade and trembling leaves provided by the poplar foliage. One would think that the Golden Oriole's penchant for such trees, its liking for the high tops, and the privacy provided by its superb - if surprising - camouflaging, would enhance its breeding success (although this combination often makes it difficult to establish whether breeding has, in fact, occurred). Unfortunately, all is not straight forward.
One reason why the fens have provided a home for the Orioles is that extensive planting of hybrid poplars took place there in the 1950's and '60's. A pair of Orioles requires between 400 and 1000 poplars, at least 7 years old, within a square kilometre, with attendant woodland edges, to encourage breeding. These plantations have attracted up to 30 pairs of Orioles over the last 30 years or so and at one point it was surmised, by Chris Mead in 2000, that perhaps the birds were 'here to stay and, with the help of global warming, (likely) to spread'? However, since 1990 a decline has taken place. Most of the early plantations are now mature, there has been extensive felling, and without replacement many will deteriorate over the next decade due to old age. Originally, trees were planted in the fens as shelter belts to reduce wind erosion of fen peat soils but an early demand for poplar wood, to make matches, has all but disappeared. Nowadays, the main use of poplar timber is for the construction of boxes and pallets, and some high quality veneers, which is sufficient to keep the industry alive but is unlikely to stimulate the new planting required to replace the ongoing felling. It remains to be seen whether the efforts of government, local councils, the RSPB etc to create new plantations, and to reward farmers for activities likely to prove beneficial to birds, will prove successful in encouraging the spread of Orioles.
The best place to miss seeing Golden Orioles is the RSPB reserve at Lakenheath. There were three singing males at Lakenheath Fen in the spring. In fact they were first heard on 27th April, significantly earlier than usual - on average they normally arrive about 14th May - which was put down to the mild weather during April facilitating their swift return from their African wintering quarters. The lovely June weather will have helped breeding success - the greatest cause of failure is bad weather in June, with nests producing three times as many fledged young in warm dry Junes as in cool wet ones - but, given that bumble bees (declining) and caterpillars (drowned), form a significant part of their diet, the disastrous July may have had a balancing effect.