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.
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.
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
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David James,
Sydney
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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.
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