So has Philip just nailed his own
coffin?? I think so, heh heh.
For an easily observable species,
such as the yellow tufted honeyeater (very obvious colour, behaviour and call),
that doesn't seem to be restricted much by habitat (see later), they are very
rarely recorded in Canberra (see Philips table). Which suggests
their population density IS low and they are rare in Canberra.
Examples Philip gave either side
of YTH such as Eastern yellow robins, rufous songlarks and skylarks are one or
more of the following, hard to observe, hard to identify, seasonal, or do not
occur in garden habitats. However, they are clearly much more population dense
in 'the city of Canberra' (not necessarily gardens)' or the ACT
than YTH (I think). Yet I suspect most people would still call these species
'uncommon' in the region. The spotted turtle dove is rare in abundance, but a very loud and
obvious/obnoxious (or just noxious) species.
The conclusion I make is that YTH
are rare in Canberra.
Yours numerously
Benj Whitworth
Sorry Peter (and others?), we may need to agree to
disagree but that is OK. I think what really matters is the number of
individuals of the species, present in the area. Of course we rarely know this.
Because of this, we use abstractions, like these words, for convenience. Yet
there is a big difference between "common" and "commonly observed". There
are so many biases involved in observability from the behaviour, habitat, size,
distinctiveness of the bird species, to the skill, effort, sense acuity and
areas visited by the observer. In assessing abundance, you should at least be
aware of these biases and filter the impressions gained through casual observing
or even serious attempts at counts, to arrive at a conclusion. That
doesn't mean that I and anyone else shouldn't like to just enjoy the rarely
observed crake just because it actually is probably a lot more common than it
appears.
I don't for a moment imagine that the abundance (in
individuals per square kilometre) of the Wedge-tailed Eagle in the ACT is
anywhere near to as many as that of the Owlet Nightjar or Tawny Frogmouth or
quite likely even the Yellow-tufted Honeyeater. Although I don't know of course.
For the purpose of the exercise, assume that to be the case, then the latter
three are far more common than the first. However we encounter Wedge-tailed
Eagles vastly more often than the others, because they are obvious at distances
of over a km, which the others aren't. This is just a rather extreme example and
would lead to the absurd proposition the Wedge-tailed Eagle is much more common
than the Owlet Nightjar, rather than just that one is very big and easy to find
and the other isn't. This is why the aspects of abundance ("common" or "rare")
has little to do with how often you observe a species. Another example is little
birds of the canopy with high frequency voices, are they rare because the
particular observer can't hear them and are they then common because someone
else can hear them?
And as for "an additional problem, how do we
describe a species that occurred only once but in an extremely large flock?" I
suggest that "occurred only once but in an extremely large flock" would make a
perfect description, maybe supplemented with date and number of birds included,
as "extremely large flock" may imply something different for e.g. Californian
Condors from Common Starlings.
Philip
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