How to explain the difference?
Saw-Whets are both migratory and nomadic
Show little faithfulness to nesting sites and
select instead an area with a high vole population (same for wintering
site?)
NSWO are present year-round on their breeding
range
Many (not all) move south in Autumn
(irruptive migrant)
There is a large fluctuation in the number of
individuals migrating each year:
Our seasonal totals have ranged from 727 in
1999 to 23 in 1997 with a 10 year average of 366
Could be result of the degree of breeding
success, but
Many adults migrate, so breeding success
alone cannot explain the irruptive nature of NSWO migration