CBC numbers are usually handled as birds per party-hour and
any set of comparative numbers is more useful with effort and
temporal components. Even so, counts with high participation
are probably never truely comparable with those that have
relatively few participants. I also think stakeout birds, bird
peculiar to a single area in a circle and birds picked up almost
exclusively by feeder counts (Anna's Hummingbird) are misrepresented
by a party-hour calculation.

The most straight forward way of measuring abundance is to compare
successive years for your own count. For the Columbia Estuary,
I find the average count and the standard deviation. Any count
higher than the average plus the standard deviation I count as
high.

I'm a very visual person, so graphs help me a lot. This is a
good qualitative way to make comparisons between counts (it can
also be quantitative if you know the calculus and stuff)
I think you'll find that a lot of this work has been done for you
at: http://www.audubon.org/bird/cbc/hr/index.html
What you'll find is that siskins, along with many winter finch
species go through irruptions and crashes that are region wide.

Jim Flynn queried:
> Hi Hugh, and all -
>
> What is the best way of measuring species abundance on a CBC? If you had
> the third highest count of Siskins, by raw numbers, does that mean they
> were really abundant this year - or that you had a lot of participants
> this year? I know that counting the number of a species and dividing by
> the number of participants that year is sometimes done. I'm curious how
> that would change the ranking. It's easy to establish new high counts
> when a CBC increases its participant total.
>
> Granted every way of measuring species abundance has some flaws, but
> wouldn't this be a more telling way of looking at local population
> changes?
>
> I don't have any totals for the Kent-Auburn CBC (divided by fancy math
> or otherwise) but they seemed to be in normal, or slightly lower,
> numbers in my particular count area.

--
Mike Patterson
Astoria, OR
celata at pacifier.com

Half-a-bee, philosophically must ipso-facto half not-be.
But half the bee, has got to bee Vis-a-vis its entity...
d'you see?
But can a bee be said to be or not to be an entire bee
When half the bee is not a bee due to some ancient injury?
-Monty Python

http://www.pacifier.com/~mpatters/bird/bird.html