"counting" butterflies (was: Tucson sightings)

[Doug Yanega]

>Ron and others,
>
>I can fully understand and I respect the concern regarding the accuracy of
>"counts".  I will, however, attempt to explain and defend "counts" a little
>in order to try and show that they may not be as ridiculous as they seem.

I'll add to this by pointing out that certain types of counts are more
useful than others. There's a textbook about a well-known British Butterfly
Monitoring project (probably still ongoing), that uses a much more sensible
system; each monitor walks the same exact personal route during the same
time window each year, under similar conditions. Results from any given
monitor are ONLY compared directly to results from that same monitor in
different years, and standardized before any comparisons *between* monitors
are made, because they assume (correctly) that no two observers are exactly
equally proficient. In other words, if monitor X is poor at spotting
skippers, and monitor Y brilliant at it, then X's reports will always be
lower than Y's even if the actual abundance at their respective sites is
the same; but by *standardizing* and using percentages rather than raw
numbers, one can say "there was a 30% increase in skipper sightings by both
monitors X and Y in 1998 versus 1997 and 1999" and feel better about it
being a real pattern.
Systems like the US butterfly counts and the famous Breeding Bird Survey
assume that all observers are equally proficient, and this severely
undermines the validity of the comparisons.

Peace,


Doug Yanega        Dept. of Entomology         Entomology Research Museum
Univ. of California - Riverside, Riverside, CA 92521
phone: (909) 787-4315 (standard disclaimer: opinions are mine, not UCR's)
           http://entmuseum9.ucr.edu/staff/yanega.html
  "There are some enterprises in which a careful disorderliness
        is the true method" - Herman Melville, Moby Dick, Chap. 82



 
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