Matt,
This is a mine field, but I’ll get the ball rolling...with some very specific examples.
Using Calendar YearCalendar Year terminology is ALL based on the year the bird was born, starting from the 1st January and is worked out by the moult stage of the bird in question.
1st Calendar Year = birds born in the year of observation. Generally, there are NO 1St calendar year birds about in Jan, Feb and March.... (e.g. a Herring Gull seen on Dec 31st 2011 which was a nestling in May 2011 would be a 1st Calendar bird, BUT would be a 2nd Cal bird the following day because of the year change)
2nd Calendar Year = birds born last year (e.g. a Kittiwake with black “W” wing plumage which is observed after the 1st Jan)
3rd Calendar Year = birds born two years ago (e.g. Herring gull with grey saddle but juvenile wing pattern seen in January)
Etc, etc...
5th Calendar Year = Bird in its fifth year (e.g. Great Black-backed Gull, looking like an adult BUT still with dark markings on the bill.)
Using the Season.When describing the age of a bird, you may chose to use a second method, based on the seasons. Both methods are correct, BUT don’t often get used at the same time, unless taking about gulls at Boston Tip.....
)
1st Winter = describes a bird with plumage obtained during the first winter period of its life (Aug-Mar-ish depending on species)
1st Summer = describes a bird with plumage obtained during the first summer period of its life (Feb-Sep-ish depending on species)
2nd Winter = describes a bird with plumage obtained during the second winter period of its life (Aug-Mar-ish depending on species)
Juvenile Plumage.The term juvenile refers to plumage of a bird that has recently fledged. However, even this isn’t straight forward. Black-headed Gull lose their juvenile plumage during a autumn body moult, BUT Iceland Gulls keep it until the following Spring......DOH!
A Confusing Mixture.....You may have recently read about a juvenile 1st winter/2nd calendar year Iceland Gull..... This is all correct BUT very confusing! This refers to an Iceland Gull seen on or after Jan 1st which retains it juvenile plumage, is in its first winter, but was born last year.... Unfortunately there are NO rules.
And, this all comes with a health warning: some species, such as Gannets have a long breeding season, and there can be over a 3 month gap between the first birds fledging and the last birds fledging. So, the plumage of two 1st Cal Year gannets can look very different, BUT they are both 1st year birds. You can age gannets up to 5 years old on wing plumage....
Some bird moult very quickly and it isn’t possible to tell their calendar year. (e.g. With House Sparrows, ALL juveniles will have a FULL moult in the autumn and the new plumage is identical to an adult bird which also under goes a full moult in the autumn. Therefore it isn’t possible to Age house Sparrows after their first moult, so NO 2nd calendar year birds...). The only way to age a house sparrow is to cut them in half and count the rings.......
Learning and understanding moult in different species of birds can be a very rewarding and interesting past-time... BUT don't get too bogged down in it!
Finally, other people use different aging systems, such as bird ringers, they use the following codes... see
http://www.bto.org/sites/default/files/ ... ecodes.pdf0 Age unknown - only to be used if data have been lost and the ringer has no idea if a bird was a nestling or full-grown
1 Pullus (Use P not 1 for pullus on handwritten schedules as a series of 1s looks like a ditto line)
1J Passerines only - fledged, but flying so weakly that it is obviously incapable of having flown far from the nest
2 Fully grown, year of hatching quite unknown (including current year)
2J Fully grown, year of hatching quite unknown (including current year), still partly or completely in juvenile body plumage (rarely used)
3 Definitely hatched during current calendar year (eg first-years in autumn)
3J* Passerines only - definitely hatched this calendar year and still partly or completely in juvenile body plumage*
4 Hatched before current calendar year - exact year unknown (eg many adults in autumn)
4I Hatched before current calendar year - exact year unknown but definitely not full adult
5 Definitely hatched during previous calendar year (eg first-years in early spring)
5J Definitely hatched during previous calendar year (eg first-years in early spring) still partly or completely in juvenile body plumage rarely used)
6 etc etc etc....
I’m sure Stuart Britton will add to this topic.
PS the method to age House Sparrows is a joke......
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