GENERAL DEFENSIVE BEHAVIOR OF PEREGRINES
General Behavior:
Territorial defense behavior fluctuates depending on the personality of the
peregrine, the time of year, location of the interaction, status of the breeding
cycle, and cause for defense. Young peregrines before they have the means of
flight will flip on their backs and present their feet as a means of defense. This
allows them to grab with their talons at whatever is trying to get at them.
Adult peregrines use intimidation in flight as the main means of chasing
perceived intruders away. This involves the falcon swooping at the intruder in
an attempt to scare it away, which with people means flying over their heads.
The majority of the time this does not involve any contact between bird and the
person. The bird will keep this up until either the person goes away or the bird
realizes that intruder is staying and stops the fly-overs. Occasionally after a few
passes, the falcon will perch nearby and watch.
During a fly-over, if the falcon actually makes contact, it does so in one of two
manners. Some contacts are with the birds brushing the person with the tips of
their wings. The other more common method involves bumping with the back of
the feet. The equivalent would be to rap your knuckles against something. The
falcons would not make any attempt to grab you with their talons.
For the most of the time that the peregrines are defensive of their territory, the
best thing to do is be aware of them and stay away.
INTERACTIONS WITH PEREGRINES
If it is at all possible, it is always best to stay away from nesting peregrines.
In Chicago, the nesting season runs from March through June. Postponing work
until after the nesting season, is the easiest solution to prevent interactions with
the birds.
Each nest site is unique in both building design and peregrine personalities.
Defensive behavior of the falcons fluctuates depending on the personality of the
peregrines, the time of year, location of the interaction, status of the breeding
cycle, and cause for defense.
In certain circumstances it may be possible to conduct work on a site even if the
peregrines are nesting. There is no standard answer in how to deal with the
peregrine falcons at a nest site, much of what can be done is dependent on the
nature of the birds as well as the type of work. Of utmost concern is the
protection of the falcons as well as the safety of personnel at the site.
For advice on peregrines, please call Mary Hennen, director of the Chicago
Peregrine Program at 312-665-7718.
BEHAVIOR OF NESTING PEREGRINES
FEBRUARY-MARCH
Adults return to nesting territories and begin courtship behavior. By the end of
March, peregrines are laying eggs. The nest is a mere depression in the gravel.
No outside nesting material is brought in. Normal clutch size is four eggs with
one egg being laid every 36 hours.
APRIL-MAY
Peregrines will incubate for approximately 30 to 32 days after the last egg is
laid. The male (tiercel) and the female (falcon) peregrine will take turns
incubating the eggs. When disturbed at the nest at this time, if the female is on
the eggs, she will remain so even if you are next to the nest. If the male is on the
eggs, he will immediately take off and fly over the intruder while the female
returns to the nest and eggs. The female may not immediately get back on the
eggs but may perch nearby.
If the disturbance is in another portion of the territory, the male may choose to
defend it in a fly-over. Usually after a couple of passes, the male will perch
where he can see the intruder and just watch.
MAY-JUNE
The eggs will hatch within 2-3 days. If after a week has passed since the last
emergence of a chick, the unhatched eggs will be retrieved by a researcher.
These are kept for analysis for such things as contaminant levels. From the time
the first chick hatches until the last chick is about a week old, the adults display
their most aggressive behavior. This coincides with when the chicks are the
most vulnerable.
The female now becomes the most aggressive of the pair. If the birds have the
personality/behavior where they will actually make contact with an intruder
during a fly-over, this is when it would happen and most likely by the female.
When you have a fairly aggressive male, he will fly at the intruder in tandem
with the female so the intruder is struck alternately by the female and then by
the male. Generally fly-overs will continue until the intruder leaves.
The chicks are banded when they are 21-24 days old. The chick’s body has
grown to full size but it is still all covered in down. This is the time when it is
safe to band because the leg will not grow any larger and the chick does not
have any flight feathers. The adults may react at their peak aggression level if
the chicks are in jeopardy.
JUNE
At approximately 42-45 days old, the chicks will take their first flight. This is
generally a glide down to a lower spot where they will perch for a few hours
while they try and orient themselves. Defense of the nesting area is now at the
level of the beginning of the season. Though the aggressive nature of the adults
has decreased, lack of disturbance to the nest is crucial as to prevent the young
from premature fledging from the nest. As the immature peregrines start flying
more, they begin ranging further and further from their natal site.