Hi all,

Posting this query again as no one replied.

I need to create a way to standardize bat sampling data in northern 
latitudes not only by the Activity Index standardized by sample time 
(unit effort) but by the constantly changing night length.

This was easy in the tropics with a straight forward application of my 
Acoustic Activity Index (AI) [Miller, B. W. 2001. A method for 
determining relative activity of free flying bats using a new activity 
index for acoustic monitoring. Acta Chiropterologica. 3: 93-105].

This uses the occurrence of each species by 1-minute time blocks and is 
then standardized by "Unit Effort"  which is the total sample time each 
night in hours. With a night length that was fairly standard with only a 
small ą of 1 hr or so for seasonal variation and very small 
night-to-night change this seem OK.

However looking at data from here in the northern latitudes,I need 
something else in addition.   The night length not only changes rapidly 
night-to-night during the summer, but has a very wide ą.  So using only 
AI -occurrences per each 1-minute time interval standardized by sampling 
time previously used in the tropics may not reflect a realistic 
comparison measure up here in the north.

So my question is how to incorporate the length of each night into the 
AI standardized by sample time?
How best to integrate the night length since that is one of the key 
factors constraining bat activity?

*/R/* seems awesome for running repetitive calculations once one has the 
code line script.  So I am trying to see how to develop such a new 
standardized /R/ code for two data sets, one a DF with the simple AI 
values that have already been standardized by unit effort and another 
that includes the ever changing sunset-sunrise data.

For working out GGplot temporal activity plots by minute for each night 
it took bit of hand holding by Hadley as R does not (or at lead did not) 
"do time well".  Not sure what can be done with standardizing the data 
with changing night lengths form one night to the.   The crossover 
midnight may not be an issue for this calculation since we just need a 
total night length in decimal hours.

Moon phase and % illumination is yet another issue, but not relevant at 
the moment.:-)

Any and all suggestions welcome and the bats will depend on it.

Bruce

-- 
Bruce W. Miller, Ph.D.
Conservation Ecologist
Neotropical Bat Projects


office details
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Stanwood, Mi. 49346
Phone (231) 679-6059



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