"counting" butterflies (was: Tucson sightings)

mbpi at juno.com mbpi at juno.com
Wed Feb 21 20:41:01 EST 2001


In response to the following" 

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.


More information about the Leps-l mailing list