Not only that (migration may differ between places) but the pattern of
migration at one location, can change over time. In Canberra it has. Although
the description of the pattern is has not changed, the quantitative
manifestation of this has changed considerably. It is for that reason that I
chose this species as one of the three to show its abundance in Canberra by
graph, monthly for the 252 months from July 1981 to June 2002 in my book:
Canberra Birds: A Report on the first 21 years of the Garden Bird Survey - page
90 (as well as the compiled monthly and long term graphs). Summer time numbers
have steadily increased, whereas winter time abundance has rapidly decreased,
particularly in the period 1992 to 1994. So the extent of migration impact has
reduced.
Although what Evan described below may not be migration at all. Just going by
his note below, I suggest it could just be daily movement of birds from day
feeding areas to night roosts. Although I wasn't there so don't know.
Philip
|
