You say potato, I say juvenile..
Just a quick note to open up a discussion or whatever, but to my mind at least, it's becoming more compelling, comparing how birders are naming the age of these Gulls than the birds themselves. That can't be right! Searching for answers online is a accident waiting to happen and my earlier attempt at clearing the issue up now looks, to some extent, misleading! That post didn't bring about any comments and continued variation in age classification is being used across the local websites; but admittedly more than one bird is involved here. Certainly, from the photos, the Pontsticill Glaucous Gull looks far more faded than the Burry Inlet bird.
Gull Research Organisation has been my latest online destination for enlightenment and I see that on their site, which is full of experts, the photos of the Gulls are classified by the subject's age in calendar years, before reaching sub-adult status and ultimately adulthood.
Is gull moult too complex an issue to use terms like juvenile, 1st Winter, 1st Summer and so on.? Should we also be using 1cy, 2cy, 3cy, etc. I can see the advantages of both; perhaps it doesn't matter?
A reference that I own is Gulls by P.J. Grant (1986) and that openly refers to periods where juvenile (summer to Oct), 1st winter (September to March) and 1st Summer (March to September) occur in Glaucous Gull and Iceland Gull. There has been progress in the understanding of Gulls since then and a good book (that I don't own) is Gulls by Olsen and Larson (2004), which may shed more light on the matter? My own recent use of juvenile, to class the gulls concerned in our area recently, is in no small part following the lead of the National Bird Alert Services who rarely deviate from classing these "1st winter birds" as juveniles. I must admit that my own persuasion is tending back to the more general guidance provided by Grant.
I suspect that when we read about a Glaucous Gull which has been reported, but not accompanied by a photo, many of us would imagine what it looked like irrespective of whether it has been classed as juv, juv/1stW, 1stW or 2cy, and that image would tend to be the same?
3 comments:
I say juvenile on the basis of my understanding that in both Glaucous and Iceland very little, if any, moult normally takes place post fledging until the the commencement of first post-juv moult in the second calendar year. I don't think that was generally appreciated when Grant produced his 1986 edition of 'Gulls'. Strictly speaking most 'first-winter' Glaucs and Icelands are 'juvenile' though it might be a little hard to judge with absolute certaintly on faded birds and reconcile that terminology by the time we reach February of the year after fledging. In which case '2nd calendar year' and so on, might be a better way refering to birds of this age. Incidentally, I agree with you Mark that the Pontsticill Res Glauc looks a lot paler than the Gower bird judging from photos. Indeed, on first impressions I even considered the Pontsticill bird might be second-winter (3rd-cal yr) but other characters indicate otherwise.
Thanks Phil, for your comments. It's very interesting and helpful to read your views on this topic.
To make things more confusing in the USA the most generally used nomenclature is the Humphrey Parkes system, too long to go into here, but I would say it has grat advantages over the other ageing systems. For those interested in gull moult and ageing I would suggest reading the moult section in The Gulls of the Americas by Howell &Dunn. It takes you through the complete moult cycle of Western Gull which is a relaxation in how hormone levels etc can change the appearance of similar aged feather as moult progresses. And yes the white wing gulls usually maintain juv plumage throughout their 1st winter
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