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John,
The
simple answer to your question is to use a system that divides number of
observations by number of surveys. This is usually given as reporting or
recording rate. There are various ways this can be done, depending on the
particular structure of the method used. The GBS Report describes this in detail
for the GBS. Same with the COG Atlas (except that like most Atlases don't
consider numb of individuals(, just presence). Most other publications unless
they just present a list of records, will explain whatever systems they use.
What works best also depends a lot on the social behaviour of the species
reported on, as well as the activity of observers in recording each species. To
be specific, your Musk Duck is one breeding record with many observations and if
others report the same, we should be clever enough to work out if they are
likely to be the same bird. Your Spotted Crakes in the little Crace wetland
is evidence that the species was present at the site over the specified period.
That suggests they are unlikely to be the same birds as others (?) observed
somewhere else over the same period. In combination this gives information about
status. As to how many records that is, I don't know that this matters a lot.
Philip
I have seen no Gang-Gangs in Gungahlin but I am interested in the answer to
Jenny’s question because I have always found this a difficult ‘ethical’ question
regarding repeated sightings generally.
I have been reporting one or both of a pair of Spotted Crakes in the little
Crace wetland virtually every week for well over a year now. It is clear they
are the same two birds. Not long ago I noticed Geoffrey Dabb used the phrase
‘now common’ with regard to SC. I know Geoffrey can access other records than
mine but it did make me wonder if my reporting helped give an impression that
SCs are common. Similarly, I could have reported the breeding of a Musk Duck
(singular) in Yerrabi Pond every day for a month if I wished (I didn’t) but how
many breeding records is that? I reported it a few times. What if other
Gungahlin members reported the same breeding event regularly?. Are Crakes, for
example, becoming more common or is the increase in observers the real factor?
It does make me wonder how often the same birds get reported and how this
influences any calculation of their frequency.
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