[va-richmond-general] 90% of trees

I was chatting with a colleague at work a few days ago about 
things outdoors. He's an avid hiker, and has recently taken 
up tree identification. He said that he had observed that 
there were about five species of trees that accounted for 
about 90% of the examples you see in our area. He posed the
following question: how many species of birds would you 
need to be able to identify in order to know 90% of the 
birds you normally run across around here.

My initial guess was about 10.  But I think I might have 
been a bit low. Here's my list, in no particular order:

Rock Dove
Mourning Dove
Starling
House Sparrow
Cardinal
Blue Jay
Mallard
Chickadee
Titmouse
House Finch

In retrospect, I think you may need 15 or 20 to do the job,
but I have no data to back this up. I limited myself to 
thinking about birds that are here year-round or that nest
here, but you could play the game with looser rules.  

Anyway, it was a fun question to think about...

Lewis Barnett
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