Last fall, there was widespread concern about low Blue Jay numbers at
Holiday Beach Conservation Area, Ontario,
where we've been counting them,
along with the hawks, for more than 25 years. The 2002 totals
for Blue Jay
ended up at "only" 72,600. From 1984 - 1997, Blue Jay numbers
have ranged
from a low of ~280,000 and a high ~420,000. BUT, the 1998 count
was
~64,700, the 1999 count was a record ~630,000, the 2000 count was ~65,700,
and the 2001 count was ~524,700. So there have been recent years
with even
lower numbers than 2002. When graphed, this data shows a clear
and dramatic
two-year cycle up and down beginning in 1998. This is quite different
from
a graph of the data pre-1998, but does not correlate well with West
Nile
Virus either. The drop in numbers in 1998 pre-dates the detection
of the
virus in New York by two years! Perhaps WNV was undetected in
the
unpopulated regions of northern Ontario (where these Blue Jays originate)
prior to its detection in New York? Perhaps there's another explanation?
While I have only a little data to support this, it does appear to be
quite
dramatic. In 2001 I began banding hummingbirds in the first week
of August
right after I got my permit to do so. Of the 52 hummingbirds
banded from
August 8 through mid-October, I did not see a single bird that was
molting.
Unlike many passerines, adult Ruby-throated Hummingbirds undergo a
complete
body feather molt prior to migration, but delay molting their flight
feathers until on their wintering grounds (Rufous Hummingbirds are
different!). Young of the year do not molt again until on the
wintering
grounds also. Thus, it appeared that the pre-migratory body feather
molt
occurred prior to August 8 in 2001. In 2002, I started banding
in May, so
was in a better position to determine molting schedules. Between
May 10 and
July 31, I banded 107 hummingbirds, all adults, and only 2 showed a
small
amount of body molt. Then, suddently, from August 6 - 30, most
adult
hummingbirds captured (37 of 46) showed body molt, most of them very
extensive. After August 30, there was only 1 (of 2) adult birds
detected
with body molt. Clearly, the body molt of adults was restricted
to a short
time period for the population as a whole, immediately prior to migration,
and also was clearly later than in 2001.
Also notably, I was detecting good numbers adult female hummingbirds
with
eggs in their oviducts as late as July 31 last year, which correlates
well
with the early season cold spell (corresponding with nest building
and egg
laying in hummingbirds), and later the drought and lack of insects.
The
number of young captured from August 2, 2002 onward was much lower
in
proportion to 2001. Another piece of data that will be published
with the
Fall 2002 Michigan Bird Survey is that there were 45 reports of
Ruby-throated Hummingbirds in October, compared with only 7 in 2001.
Also,
two hummingbirds lingered into November in Berrien Co. (both of which
I
banded - adult females surprisingly), one remaining until a record
late date
of November 21. So, I am convinced that the cold wet spring and
dry summer
with no insects probably caused almost complete failure of initial
nesting
attempts in this species, resulting in much later broods than most
years,
creating a domino effect of later molt, and later migrants.
Allen Chartier
amazilia1 AT comcast.net
1442 West River Park Drive
Inkster, MI 48141
Website: http://www.amazilia.net
Michigan HummerNet: http://www.amazilia.net/MIHummerNet/index.htm