I have read with interest recent posts relating to early migration and
questions on populations this year. While these are different issues it is
possible there is an interrelationship unknown to us at this time. While the
subjects are much more complicated than space allows here, I wish to get
some thought processes started in bird behavior and their conservation
needs.



Bird numbers were down considerably this spring along the Lake Erie coast,
nearly 40% from average. This appears to have been widespread with migration
stations from Minnesota to the east coast indicating similar reductions. The
cause isn't as easy to ascertain unfortunately. While there is always some
variation in where birds pass through and in what volume, this across the
board reduction is reason for concern. We will be watching fall age ratios
as we begin the fall migration banding program here at Black Swamp Bird
Observatory. A major increase in young to adult ratios may indicate low
breeder numbers as suggested by spring passage numbers and the expected high
productivity associated with a rebounding population. Time may allow us to
look back for the answers we seek.



While we have spring migration down to a fine art in timing (you name the
species of passerine and we can give you the time frame most likely to
encounter it) fall migration has remained a bit more difficult. Different
environmental parameters and species motivators are in action during the
southward migration than what we see in the spring. Spring is governed by
day length and reproductive behavior. For fall, there is the primary driver
of day length, but a host of other factors such as age, sex, actual breeding
timing, food resources, post-breeding condition, and several actions that
could be considered forms of "migration". The biggest complications for
observers of theses "migration movements" is post-breeding dispersal and
fledgling dispersal movements or "migration". These may represent a staging
of local birds or an actual migration. This "migration" is generally
northward in direction. In most locales this isn't noticeable, maybe a
sudden influx of birds or of an individual not known to breed in an area.
Along the Lake Erie coast these "dispersal migrations" are quite evident.
These northward movements of young of year birds are observed in almost all
bird groups. All recoveries of banded Ring-billed Gulls (RBGU) following
fledging near Maumee Bay colonies were in the Saginaw Bay area of Michigan
until late summer when birds retuned to Lake Erie and continued their "true
migration" to the Atlantic Coast. Color-marked Purple Martins (PUMA) from
over 40 colonies in east-central Ohio were recorded moving northward through
the colonies and then at the large roost at Presque Isle, PA in the early
fall before heading in a "true migration' to South America. Large influxes
of passerines from Yellow Warbler (YWAR), Baltimore Orioles (BAOR), Eastern
Phoebes (EAPH), and swallows can be observed each August along the Lake Erie
coast.



Understanding the different movements birds have increases our understanding
of their behaviors and can lead to a greater understanding of their needs
and hence improved conservation. While not all, much of the threads I have
read on this list-serve appear to represent this local or northward
dispersal migration common for late July and early August. Identification of
these concentration or "staging" areas are an important part of their life
cycle needs and can be extremely important in bird conservation now and into
the future.





Mark Shieldcastle
Research Director

Black Swamp Bird Observatory

13551 W SR 2

Oak Harbor, Ohio 43449

419-898-4070



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