[R] Identifying peak periods of observations in circular yearly data

Jim Lemon drjimlemon at gmail.com
Wed May 27 11:34:04 CEST 2015

Hi Daisy,
You face a problem similar to one with which I have grappled in
different fields. The year is designed for the northern hemisphere,
beginning and ending in less productive biologic states in those
regions. I have previously argued that since the calendar year is an
arbitrary progression, it makes more sense to redraw the annual
boundary when examining things like this in the southern hemisphere.
That is to say, a "year" is conventionally marked at about the
northern winter solstice. Down here, this becomes the summer solstice
and breaks up a lot of things that happen around that time. Have you
thought of defining a southern bird-watching year as beginning and
ending at the southern winter solstice? As I am currently writing in
an entirely different context, it shouldn't really make much


On Wed, May 27, 2015 at 4:35 PM, Daisy Englert Duursma
<daisy.duursma at gmail.com> wrote:
> Greetings,
> I am trying to identify at which point during the year 80% of bird breeding
> observations are. typically I would answer a question like this by finding
> the median or quartiles but how do I deal with situations where the 80% of
> the is from day 285 through day 366 (leap year) and extends to day 30?
> The data is circular and and day 365 is as close to day 366 as day 1.
> I am reading the manual for CircStats and circular but I could really use
> some help on this.
> Here is some dummy data:
> obsDay<-c(rep(1:30,10),rep(45:65,2),65:180,rep(181:265,2),rep(266:330,4),rep(331:366,6))
> plot(density(obsDay))
> --
> Daisy Englert Duursma
> Department of Biological Sciences
> Room W19F 135
> Macquarie University, North Ryde, NSW 2109
> Australia
> Tel +61 2 9850 1302
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