G'day David,
Thanks for the awesomely elaborate response. You've answered my questions
and provided me with much more. Until your email I never realised that
describing moults and plumage was such a complicated process.
I guess what was confusing me a little is that I assumed that where birds
plumage are referred to as being 1st and 2nd years, I was sub consciously
thinking of a calendar year rather than the first year of the birds life.
And if I've read what you're saying correctly, these years contain cycles
that aren't necessarily related to a calendar year as we see it as these
birds in some cases may breed most of the year or all year round.
I think I erred this way because I was thinking of birds that have a
definite breeding time period every calendar year, and what I've now learned
is that their cycle of moult, can be expected at certain times of the year.
So I guess in those cases them you could reconcile the 1st and 2nd year
plumages with the calendar year, but not so with Silver Gulls in Sydney.
The background about Dwight and and the differences in the models
explain so much. I was conversing with someone in the US a few months ago
about birds over there and he tended to use terms I hadn't heard before
like, winter and summer plumage, and referring to eclipse plumage as
alternate plumage, and juvenile as basic plumage. I thought at the time that
it must be what they say over there, but I wonder now if his information was
based on the model?
Regards,
Mark
From: David James
Sent: Monday, 6 June 2011 11:08 AM
To: Mark and Amanda Young; 'birding aus'
Subject: Silver Gull - 1st immature breeding.
Hi Mark,
Silver Gull is not likely to breed in "1st immature breeding plumage". The
explanations to this and your other questions are both technical and messy,
and likely to bore most readers (hint).
Plumages are introduced by moults and there is a sequence of moults and
plumages. These follow complicated patterns and different groups of species
do it slightly different ways. To understand these patterns ornithologists
have developed conceptual models and accompanying terminology. There is more
than one model, and no model is correct, but some are better (or more
accurate) than others. Since more accurate means more complicated it also
means less general appeal.
There are two general models, that of Dwight (1900) and Humphrey and Parkes
(1959). Both have variations that I'll get to later. they use different
terminology.
Starting with the growth of the natal down, all birds moult from one plumage
to the next. Note that a moult includes the shedding of old feathers and
the growing of new ones. Each feather can be said to belong to a
'generation' that is defined by the moult it grew in. Each moult can be
'complete' (i.e. involving all of the feathers) or partial. Partial moults
typically include the contour feathers (i.e. head, body, coverts) and omit
the flight feathers, but it varies widely. The two most frequent patterns
are birds that have one complete moult a year, and birds that have one
complete and one partial moult each year (but in some species the cycle is
more than a year and in a few it is less than a year). Gulls have two moults
per cycle. Once a bird is already adult, a complete moult leads to an adult
plumage of a single generation, but a partial moult leads to an adult
plumage comprised of two generations of feathers.
Dwight linked plumages to the breeding cycle. Thus he said that a bird with
two moults per year has a breeding plumage and a non-breeding plumage. It
turns out that most birds with two moults per cycle have a partial moult
before they breed and a complete moult after they breed. Therefore adult
birds wearing one complete generation of feathers are said to be in "adult
non-breeding plumage" and those with two generations (tail and primaries
grown in a complete moult and then body feathers grown in a subsequent
partial moult) are said to be in "adult breeding plumage". Projecting this
terminology back to pre-adult feathers you get "immature non-breeding
plumage" and "immature breeding plumage". It is not intended to mean they
breed in immature breeding plumage", just that this plumage is in the same
stage of the cycle as sexually mature birds in "adult breeding plumages".
Where there is more than one cycle of immature plumages they are modified
with sequential numbering: 1st immature non-breeding, 1st immature breeding,
2nd imm non-breeding, etc.
Dwight also thought that of moults as points between plumages. Thus he named
the moults 'post breeding moult' and 'pre-breeding moult'
Dwight's model has some inherent problems. Others recognised that 'breeding'
and 'non-breeding' terms are a problem and suggested 'summer' and 'winter'
and 'eclipse'. This replaces one problem with another, since moults evolved
to renew feathers, not signify seasons.
Humphrey and Parkes sort to make a model that reflects the evolutionary
origins of moults in birds. They introduced a terminology that removed the
association between breeding, sexual maturity, seasons and so forth with
plumages and moults. Therefore the terminology is novel and many people find
it unappealing. It goes like this. The single generation of feathers
obtained by a complete moult is termed the 'basic plumage' and the plumage
of two generations created by a partial moult is called an 'alternate
plumage'. Instead of referring to adults, they used 'definitive basic
plumage' and 'definitive alternate plumage' for birds that had reached the
final stage of plumage. For younger birds they did not use immature but
still numbered the plumages sequentially: 1st basic, 1st alternate, 2nd
basic, 2nd alternate... definitive basic, definitive alternate. Thus the
model allows for sexually mature birds to breed in non-definitive (so called
immature) plumage and for sexually immature birds and post-breeding birds to
be in definitive plumage without breeding. The moults are defined by the
plumages they introduce, never the ones they replace: 1st pre-basic, 1st
pre-alternate.
Superficially it seems like just a change of names, but in reality Dwight's
model does not apply to all cases and can be very muddled. The semantics
allows the mind to understand the patterns and classify each case - the
better the semantics the more consistency. The original Humphrey and Parkes
model had a major flaw which has been corrected since HANZAB III was
written, but the required adjustment to make the model right is
unfortunately very messy and confusing.
Dwight was adopted world wide. Humphrey and Parkes supplanted it in the new
world, but did not take off in the old world. The Birds of the Western
Palearctic (BWP) used a system modified from Dwight. Australian field guides
and literature have also followed the Dwight system. HANZAB followed BWP,
but in the text it also named plumages and moults according to Humphrey and
Parkes (because it is better). So you will see in the plumages text for
Silver Gull in HANZAB that your birds are labelled in brackets as first
alternate and definitive alternate, with no prediction or reference to their
sexual maturity or breeding condition, or the time of year.
The reference on page 534 is to birds that are sexually mature but have not
had much nesting experience. Such birds are likely to be in "definitive
alternate plumage". but you can't predict this just from the knowledge that
they are breeding.
David James,
Sydney
==============================
From: Mark and Amanda Young <>
To: 'birding aus' <>
Sent: Sunday, 5 June 2011 10:15 PM
Subject: Silver Gull - 1st immature breeding.
G'day everyone,
This link is to a picture I took of 2 Silver Gulls. http://bit.ly/lYaTec
Using HANZAB as a guide, it has the bird on the left as a 1st immature
breeding, and the bird on the right as an adult in breeding plumage. My
question is does anyone know if the bird on the left will actually breed
whilst in this plumage, or will it wait until it gets its full adult
breeding plumage before it breeds? (Could they be the birds that are
referred to on page 534 where it says 'Gulls breeding after first peak
[breeding] mainly inexperienced birds'?)
And why is it called 1st immature breeding plumage when it looks more like
the 1st immature non-breeding rather than the adult breeding plumage?
Regards,
Mark
===============================
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
http://birding-aus.org <http://birding-aus.org/>
===============================
===============================
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
http://birding-aus.org
===============================
|
