2002 - Midwest Peregrine Falcon Restoration Project

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The evidence suggests that a few pairs may nest undiscovered each year, but it is
clear that the number of unbanded adults on territories is consistent with the number of
unbanded young fledging from known nests. There is no evidence of an undiscovered
population on the order of 10% to 20% of the known population.
It has seemed likely that close monitoring and banding of the peregrine population
in the Midwest would ultimately cease as more and more pairs found places to nest
undetected and the population became increasingly unbanded. However, if there is no
substantial undetected population, the proportion of unbanded adults should not increase
unless monitoring and banding taper off. So far that has not happened; unbanded young
in 2002 were 14.8% of the total fledged, consistent with the long-term record. Why
should we continue to keep track of the peregrines? There are at least two good reasons:
first, peregrines are magnetically attractive; watching them and banding the chicks is
intensely satisfying. Also, the database on Midwestern peregrines becomes more
valuable scientifically each year with the addition of new information. Monitoring and
banding at the current level of intensity in the Midwest can continue indefinitely, if the
will persists.
Weather and Peregrines Nesting on River Cliffs
The three pairs of peregrines nesting on the west side of the Mississippi, on eastfacing
cliffs, hatched their clutches on May 21 (Queens Bluff), May 23 (John Latsch),
and May 27 (Lansing, IA). The three pairs on the east side of the river on west-facing
cliffs hatched their clutches on June 14 (Castle Rock) and June 18 (Maiden Rock and
Maassen Bluff). Apparently at least two of these pairs (Maiden Rock and Maassen Bluff)
lost their first clutches early in incubation and re-nested, a process that usually takes
about two weeks from loss to start of egg-laying. At Castle Rock, the female was a oneyear-old;
the late hatch may have been the outcome of a late start typical of the first
nesting attempt by a young female. What might have caused simultaneous nest failure
for two pairs on west-facing cliffs spaced about 20 miles apart, while three pairs only a
few miles away on east facing cliffs succeeded with their first clutches? Apparently the
failed clutches were lost in a storm. Snow or rain driven by west winds would drench
cliffs facing west while those facing east would be somewhat sheltered. A major storm
passed through the area from Red Wing, Minnesota, to La Crosse, Wisconsin, on April
21, timing consistent with the nest losses.
It was 91 degrees in Minneapolis on April 15. On April 21, a record 6.2 inches of
snow fell. A peregrine incubating eggs at NSP Riverside, Minneapolis, was
photographed covered with snow on April 21 (John Tradewell). Assuming nest failure
on April 21 at the river cliffs in Wisconsin, add two weeks to start of egg-laying, a week
for egg-laying, five weeks for incubation, and the estimated hatch date would be June 16.
The three successful pairs on the east-facing cliffs (and probably also the pairs that failed)
were about one week into incubation on the date of the storm, April 21. (All of these
nesting dates are estimates made by back-dating from age of chicks at banding.)
Reading Bands
We band young birds primarily to learn about events later in their lives. Color
bands make it possible to follow the lives of individuals by reading their bands without