Part 2. Addressing some minor matters:
The words ‘phase’ and ‘morph’ are not interchangeable, although they sometimes
get used as though they are. HANZAB (Vol 1, 1990) defined ‘morph’ as “one of
two or more well-defined forms in the same populations of a species. I would go
further and say that in birds it refers to one of different colour phenotypes,
the outward expression of different forms based on genetic variation within a
single gene pool or population. ‘Phase’ implies a temporal component, a
temporary position or a transitional state. It has been used for different age
classes (transition from juvenile to adult) and also as a substitute for
‘morph’. ‘Morph’ does not imply temporal change and cannot be applied to
age-related variation, but it does not exclude individuals from changing over
time. ‘Phase’ is no longer widely used in technical literature because of its
ambiguity.
Simon Mustoe wrote:
<HANZAB plates very clearly depict the rufous phase of Brown Falcon as having
yellow cere and orbital ring. Though the text misleadingly, only refers to grey
or white. So I assume there is a common precedent amongst the rufous forms to
have this yellow bare part colouring. >
My response:
The plate of the rufous morph in HANZAB shows a yellow cere, but it is a plate
of an individual bird, and nowhere is it claimed that all rufous morph birds
have yellow ceres. The descriptions of plumages and bare parts in HANZAB are in
the plumage and related matters section so this is where you should go to see
if HANZAB says that all rufous morph adults have yellow bare parts. The
descriptions in the field ID sections are summaries of important features and
do not necessarily address all of the details. HANZAB was not misleading on
this count, but it does contain errors and mistakes and it can be difficult to
interpret. I note a mistake in the HANZAB plate of perched Brown Falcons where
image 7 of a juvenile rufous morph bird is labeled as “Adult male rufous
morph”.
Stephen Debus wrote:
<Yellow cere is a character of fully adult males, and seems to be particularly
prevalent in pale-plumaged individuals (e.g. remote areas like the Centre),
perhaps where the falcons live long enough to develop the 'old male' characters
of yellow cere and eye-ring, and white breast. See: McDonald PG (2003)>
My response:
McDonald and HANZAB both identify that yellowness increases with age more
frequent in males, but neither say it is exclusive to males. HANZAB notes
tentatively that it is may be more marked in males while McDonald claims to
have proved it is more prevalent in but not exclusive to males. However,
McDonald’s arguments are slightly circular. He wrote that all adult males and
all adult females had at least some yellow in the cere. But he aged all of
these birds on their plumage and bare parts patterns. He noted that birds breed
in what he termed “immature” plumage, and presumably these sexually mature (I
would call them adult) birds had “immature” greyish ceres. In fact, this line
of reasoning merely confirms that McDonald’s ageing methods proved to be
consistent with his ageing results. Whether his sexing techniques are similarly
circular is difficult to assess from the paper.
Stephen Debus wrote:
< My remark about longevity was on the assumption that birds in more
human-populated areas are more likely to die younger, i.e. get road-killed,
shot, trapped, poisoned (from eating carrion baits or poisoned
rodents/rabbits), collide with fences/powerlines, get electrocuted on power
poles etc.> ... and ... My comment about longevity (or causes of death) might
partly answer David James' remark about lifespan in the inland.
My response:
I still don’t buy it. The assumption that mortality rates are higher in
human-populated areas may be plausible, but a resulting complete restructure of
the population doesn’t fit the evidence. It flies in the face of a few simple
principles. first, under this hypothesis there would be more pale birds away
from populated areas, and darker birds close to populated areas, along the
coast and in the interior. Second, Brown Falcons are common to abundant in
populated rural areas; if they were suffering human-induced elevated mortality
rates sufficient to change the population structure they would also be facing
rates sufficient to change the population size – i.e. they would be rare.
Third, if adults were not surviving there would not be increased numbers of
immatures because eggs would not be laid. The specimen record dates back a
hundred years or so to when the human population was sparser. This could be
used to test the hypothesis that there has been
a change in population structure of BFs in areas densely populated by humans
compared to areas with low human density. I doubt it would survive the test.
Jeff Davies wrote:
a given population of Brown Falcons say at Werribee or where ever, does not
consist of a number of different morphs. The differences in plumage are
primarily the result of differences between the sexes overlaid by increasing
paleness as the individuals get older.
My response:
Lets be clear, Paul McDonald makes this claim, but his study does not apply to
any given population, only to a single population at Werribee, where he
reputedly (but maybe not) found no morphs.
Jeff Davies wrote:
Yellow cere is apparently only found in the older males especially the pale
Central Australian population, Stephen suggested this may possibly be because
they are for unknown reason more likely to reach the prerequisite older age.>
My response:
McDonald did not say that the cere is yellow only in old central males. On the
contrary, he wrote that he recorded it in males and females in coastal Vic,
though mostly in males. Evidence that Jeff is compiling from photo collections
seems to indicate that most, maybe all, rufous morph birds in the interior have
yellow bare parts. This presumably includes females. Unless of course the photo
sample shows males only, which seems unlikely.
Paul McDonald wrote:
<Differences according to region on the record are most likely due to
incomplete sampling, or sampling that is influenced by recent events at given
locations, e.g. marginal/ephemeral areas are more likely to have lots of
younger and thus darker birds, established areas older, lighter birds that hang
onto territories for consecutive years and so on.>
My response:
This is ironic. Paul rejects morphs continent-wide based on a study at a single
location across a short 3 years with a fairly small sample size in a habitat
that is artificial, though perhaps productive rather than marginal, considering
that it is bog farm irrigated through droughts. Surely Werribee bog farm is a
more stable environment than the flood and drought cycle of the interior, the
over grazed savannah rangelands, or the ever diminishing woodlands.
Richard Nowotny wrote:
<It does however raise the question (alluded to by Stephen [Debus] in his
response) of whether there really are "pale-plumaged" individuals, implying
that there are also darker-plumaged individuals of similar age (rather than
them being just fully mature individuals which are intrinsically pale by virtue
of their age). Can anyone comment on this?>
My response: To summarise my argument, of course there really are pale and dark
plumaged birds corresponding to morphs, but the pattern is complicated by
strong influences of geography, age, sex and individual variation as well. The
system is complex. The morphs are not absolute, but there is value in
recognising them so that the patterns of variation can be better understood.
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