[mou] Median arrival dates

[John Green]

    This is a message from Jan Green on John's email.

    The MOU net discussion about bird migration dates has been 
interesting.  But there remains a question that needs to be answered.  
What migration dates do birders want - the usual or the unusual?  Or 
both?  When the data for Green and Janssen's Minnesota Birds were 
compiled, we tried to do both with the relatively meager information 
available in the early 1970's.  Obviously much more information from 
birders is available now.
    The Seasonal Report column in The Loon published first and late 
dates yearly with a comparison to the median early or late dates for the 
past 20 years.  These extreme dates tell something about the timing of 
migration but they do not represent the bulk of the migratory activity 
when most birds are moving.  This can be the most significant information.
    One way to do this is by a bar-graph, similar to those in the ABA 
birders' guides.  Many states have produced a temporal bar-graph in a 
state check-list which partitions the timing of migration into 4 to 6 
categories of abundance or likelihood to encounter.  Sometimes these are 
organized on a geographical basis like north and south.  New Hampshire 
Audubon just produced a simple one called "A Checklist of the Birds of 
New Hampshire".  It would seem that the MOU data files have enough 
information to do something similar.

Jan Green