Bruce, Standardizing might not be the best way to go if you have low counts. You can possibly assume that events follow a homogeneous Poisson process and rate varies with night length (linear or quadratic) [Y|x ~ Poisson(phi); log(phi)=f(x)]. You can estimate corresponding coefficients by glm(). I think controlling for night length differences work even if you throw in other covariates as additive effects on the log scale.
You can get sunrise /sunset times from maptools::sunriset, be careful with timezones though. Cheers, Peter -- Péter Sólymos, Dept Biol Sci, Univ Alberta, T6G 2E9, Canada AB soly...@ualberta.ca, Ph 780.492.8534, http://psolymos.github.com Alberta Biodiversity Monitoring Institute, http://www.abmi.ca Boreal Avian Modelling Project, http://www.borealbirds.ca On Wed, Jan 23, 2013 at 7:16 PM, Bruce Miller <batsnc...@gmail.com> wrote: > 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 > 11384 Alpine Road > Stanwood, Mi. 49346 > Phone (231) 679-6059 > > > > [[alternative HTML version deleted]] > > > _______________________________________________ > R-sig-ecology mailing list > R-sig-ecology@r-project.org > https://stat.ethz.ch/mailman/listinfo/r-sig-ecology > _______________________________________________ R-sig-ecology mailing list R-sig-ecology@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-ecology