Gull
Identification
I
think that most birders would agree that identifying adult gulls,
especially those in alternate plumage, is relatively straightforward.
That is far from the case, however, when it comes to identifying
birds in various stages of subadult plumage.
This
is the time of year when many of these challenges present themselves
especially given the number of organized trips to gull hot spots such
as the Niagara River, the north shore of Lake Ontario and even the
local hot spots here in the Kitchener/Waterloo area. I am amazed at
how many birders seem to say with absolute certainty “second year
Iceland Gull,” “first year Lesser Black-backed Gull” and so on.
The
two principal references I use are Gulls of Europe, Asia and North
America (Klaus Malling Olsen and
Hans Larsson) and Gulls of the Americas (Steve
N.G. Howell/Jon Dunn), and I have several other references on my
shelves.
Let
me just quote several statements from these substantial,
comprehensive and first class works. First from from Olson/Larsson:
The
large 'four-year' gulls show great variation in the time they take
to develop into adult plumage. Age
classes between first summer and adult should be regarded as
generalisations only. (Bold
type in the original).
Grey
and brown tones look different under different light conditions.
Only
by direct comparison – best in pairs – is sexing advisable.
...head
and bill in the large gull complex have been introduced as
characters separating subspecies within the Herring Gull complex,
but the use of characters remains tentative.
In
judging photographs – the angle of the bird relative to the
photographer, the light, the film type (obviously now superseded),
equipment used and even processing methods may each result in
subtly different shades of grey
From
Howell/Dunn:
Birds
are categorized by cycle only, i.e. First cycle, second cycle etc.
It
should be accepted that the magnitude of variation in many large
white-headed gulls – compounded in some cases by hybridization –
means that a large proportion of large gulls cannot be identified
to species (or parentage) in the field.
Environmental
factors may operate directly on the gull or may be indirect but
affect the observer's perception.
Photographs
on page 254 “Presumed first-cycle Kumlien's Gull......"
Photographs
on page 254 “Probably not safely separable from Iceland Gull."
Photograph
on Page 159 “Small-billed birds like this can be confused with
Thayer's Gull."
I
could cite other examples but I think that the point is made.
Identification is far from easy and subject to a percentage of error
which is probably significant from birders lacking sufficient
expertise, whether they acknowledge it or not. I have been present
when birders claim to identify gulls in myriad plumages as easily as
they identify robins and chickadees in their yard.
Clearly
this is impossible and I take all of the reports with a very substantial grain of salt. I think that there is as much alchemy,
supposition, auto suggestion and the simple desire to correctly
identify everything as there is precise identification of species.