Terms of abundance

["Philip Veerman" <>]

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