terminology on abundance and recording rate

To: <>
Subject: terminology on abundance and recording rate
From: "Philip Veerman" <>
Date: Sun, 13 Mar 2005 16:40:41 +1100
Someone suggested that "The first words (rare, common) refer to the likelihood of seeing a species in the ACT." I dispute that the word "common" means (or should mean) "high frequency of being seen" (this being another term for recording rate, except based on just the visual). That is only a consequence. "Common" or not, should indicate population density (or abundance). In contrast, recording rate is something entirely different.
The first example that comes to mind is not a bird: The program "Big Cat Diary" often makes the point that the leopard is by far the most common of the 3 big cats in Africa, although it is much less often seen than the other two, the lion and cheetah and that is because of their behaviour. Back to local birds. The GBS Reports (pages 31 to 34) discuss this aspect in detail. With graphs for 12 species comparing the monthly abundance from the GBS to the monthly recording rate during the same 3 year period of the COG Atlas, with accompanying text that explains why in some species the graphs look similar and in others they are quite different. It relates to habitat use changes and social behaviour changes over the year.
The GBS happens to highlight these things with the A value, R value and number of records (which on one year is the F value) statistics. It is wrong to think there is a direct correlation between the abundance, observability and recording rate, except in the crudest sense.  My GBS Report presents a graph (Figure 33) of the relationship between recording rate and abundance for all species on each year. I called it "probably the most important result of the GBS". It is explained therein that the relationship varies mainly according to the social behaviour of the species concerned. Recording rate is strongly influenced by visual and sound conspicuousness of the bird or its behaviour. Not to mention the enthusiasm of people to submit records. Looking at the ABR, one would think many species that we know to be common, appear to be rare, because people are not interested to record them. But when we do get a Lewin's Rail at Commonwealth Park it may appear on that scale to be almost common, as many people go to see it, so it potentially has a high recording rate. Recording rate does not distinguish between obvious species occurring at low densities and inconspicuous species occurring at higher densities. I encounter the Wedge-tailed Eagle far more often than the Yellow Thornbill but I am sure there will be more of the latter in the ACT. Even though biomass, as in grams per hectare may favour the eagle!
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