So are Autumn Swifts Identifiable?
This is a topic which really interests me, as having been confronted with a late scaly swift in the past, I know how difficult it can be to judge the various criteria associated with their ID.
One of the problems I encountered when researching my own swift a few years back was that over the years, a level of contradiction seems to have crept in to literature in regards to what actually separates Pallid and Common swift in the field.
I do not have the Lewington article to hand right now, but I seem to recall it saying that Juv. common swifts are "blacker" than adults. Other articles since seem to say that they are actually "paler". Ross's article goes some way towards tackling the perception of ground colour in swifts, but personally I think any attempt to apply a colour scale to these birds is probably pointless. Light conditions across the potential range of vagrancy are simply subject to too much variation.
The "original" criteria of heavy set body and hips and blunter, thicker wings of Pallid swift, may well hold true, however I have seen plenty of shots out there where Pallid looks quite slim and sleek and sharp and thin winged.
A birds posture will morph from second to second, so I personally think this is also of limited use. Recent articles suggest that the degree of overlap in terms of wing structure is significant.
The pattern of the belly feathering should be straightforward, however I have seen plenty of shots of what presumably (assuming correct ID in the first place) are Pallid swifts, where the 3 stage pattern to the feathers are not visible. (Maybe that pattern is there and not resolved enough in the shots...or maybe it is not present at all). Does that final pale fringe wear away quickly on some birds?
I think one of the best descriptions I read in one of the older articles, was the use of the word "cuttlefish" for these birds.
They change their appearance from second to second at such speed, that even good quality photographs seem to cause confusion. Which puts observers in a real bind. All the time I see people saying "These are much easier in the field than in photographs".......When has that ever been considered OK by the wider birding populace? We are just asking for trouble with that scenario.
With my own bird, I always said that the shots never mirrored the bird in life. When that bird came over us first, the striking waved, marbled, scaled appearance was mind blowing, and the sandiness of the plumage seemed such a banker for Pallid. The pale throat was huge and blended into the head and body. No sharp demarcation at all. And that eye mask....It just popped out at you!
By the time we got a camera onto the bird, both the bird and the light were at such an angle, that shadows were constantly being played down the body of the bird. In some shots produced you would swear the bird had no pale throat even. So a camera can all too easily put an observer in the un-enviable position of saying "Well it looked much better in the field".
Owen