Friday, 12 September 2014

Migration through the dimensions

This is about birds (mainly).  Some snaps of animal migration are here.

Since we moved to Carwoola I have kept a record of the number of bird species seen in the area each month. To begin with I just did this myself but other residents of the are have joined in, some regularly others on an ad-hoc basis.  I put out a summary report each month through a separate blog and about January each year do a multi-part review of the previous year.  This includes a chart showing the average number of species in a month compared with the most recent 12 months.

To some extent the chart reflects observer effort in the area, as some observers migrate for part of Winter.  The very low numbers in July 2014 certainly reflect the absence of observers.

We are now at the time of year when the birds which migrate start to return and I have a special post on return months in 2004.    This led me to wonder what the impact of the migratory species is on the total number of species seen in a month.  As a definition of 'migrant' I have taken the classification evident in the COG Annual Bird Reports.

The changes in number of species observed due to the return of migrants is well illustrated in this chart.
It is also interesting that the number of non-migrant species seen per month looks very close to a constant.  As it does in fact vary from 67 species in July to 81 in October, this is to some extent an optical illusion.  (When touring Radio City Music Hall in 2005 we were told that a similar principal applies to the line up of the Rockettes as mentioned in the linked post.)

The evidence of some mgrant species in mid-Winter (the red area doesn't completely vanish) reflects some migrants arriving in the area in Winter having fled the (even) worse climate in the mountains.  These include Flame Robins, Golden Whistlers and Australian Shelduck (although the Shelduck are now appearing year round in areas where food is easy to obtain (eg lucerne paddocks).

All of this migration is through a spatial dimension.  I was thinking about how plants don't migrate but then started to wonder if the regular appearance and disappearance of some plants could be regarded as migration through time?  That needs more thought and one alternate hypothesis is that they change form: full plant - seed/storage organ - full plant.  Whether this is more akin to

  • transmutation (a la Philosophers Stone);
  • cyborg tricks (a la Terminator); or
  • shape shifting (take your pick of many witchcraft beliefs)

is also open to debate.

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