Wednesday, June 6, 2012

If we were on the mainland a very brief, through-a-window view of a middling sized, dark winged, yellow rumped bird undulating down a net ride would probably turn out to be a Green Woodpecker. On Bardsey it was almost certainly a Golden Oriole as these are recorded annually (there has only been one record of Green Woodpecker since the early 1980s). Sadly the bird was not seen again. One, possibly two, unrung Common Rosefinch have put in brief appearances and the Melodious Warbler continued to sing up until yesterday. Bird of the day was a Red-breasted Flycatcher at Nant. Of approximately 75 previous Bardsey records only nine have been in spring, all but one in June.

There have been some interesting studies into the body mass of long distance migrants. Chernetzov et al 2007, compared the body mass of Red-breasted Flycatcher and Blyth's Reed Warbler, two species which have to cross the arid belt of Western Centrel Asia in Spring and Autumn. Blyth's Reed Warbler had a much greater relative body mass prior to the crossing than Red-breasted Flycatcher, but they both have to cross the same distance. So why would one species need more fuel reserves than another? The answer is foraging ecology. Flycatchers can't catch flies if they're carrying too many grams. It would be like an obese human having to jump into the air to catch cheese-burgers. Sort of. Similar observations were made on the Spotted Flycatcher, before, during and after crossing the Sahara. So flycatchers just have to gain mass at low rates and hope that they encounter plenty of insects along the way. Unfortunately we did not catch today's Red-breasted Flycatcher, but the one we caught last Autumn had a fat/pec score of 0/0. Perhaps it was a score not as bad as it seemed. (c) Richard Brown

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