Hardly a day goes by now that I don’t find a few discarded
blue jay or mourning dove feathers on the ground in our small
front yard. Obviously this indicates which two species of birds
tend to be dominating our feeders these days. It also tells us
that the adult songbirds in general have begun their complete
molt that follows nesting.
Birds have something that no other creatures on earth have –
feathers. Wear and tear on these rather fragile objects during
the demanding period of five or six months that includes
migrating long distances northward and nesting can be quite
severe.
Day-to-day flight, hitting against branches and leaves,
defending the nest and finding food for themselves as well as
their young can be very hard on feathers. These activities
themselves, in addition to molting, may cause them to loosen in
their follicles and drop out. Fortunately a feather germ at the
base of each follicle promptly starts the growth of a new
feather.
Three important periods in the lives of songbirds include
migration (both northward and southward), reproduction, and
molting. Each must be accomplished separately and, ideally, at a
time when the individual birds are able to obtain the necessary
food to remain alive and strong.
Early August is when many songbirds that we’ve been feeding
and observing throughout the late spring and summer begin their
so-called post-nuptial, or "after mating," molt. Under
ordinary circumstances a bird during the period of molt will lose
only a few feathers at a time. Most often the corresponding
feathers on opposite sides of the body will be shed
simultaneously in order to keep the bird in proper balance for
flight.
It is during this molt that all of their feathers will be
eventually lost and replaced. Around ten weeks are required for
a purple finch, for example, to grow a new coat of feathers.
Golden eagles will require two full years to complete their
molt. Most species of songbirds molt their wing feathers only
once a year, usually at the end of nesting. Cranes on the other
hand will molt their wing feathers only every two years. In
spring small songbirds will molt many of their body feathers
excluding those on the wings and the tail, referred to as a
partial molt.
Some waterbirds, including ducks, geese, swans, loons, grebes
and others, lose all of their wing primaries at once, leaving the
birds flightless while their young are developing. This is
nature’s way of keeping the adults with the young! These
flightless adults nevertheless can dive, swim and forage for food
and avoid predators. This manner of molting would obviously
never work with songbirds.
A song sparrow’s total plumage includes between 2100 and 2200
feathers. Naturally this amount varies from summer to winter
when more feathers are needed for warmth. Around 940 feathers
adorn a ruby-throated hummingbird while a tundra swan carries
slightly over 25,000 feathers. Imagine the energy required to
replace all of those feathers.
What a physiologically demanding time a complete molt is for
birds, a very energetically costly period for these creatures.
Breeding physiology wanes and off the feathers come while warm
weather still remains and the birds are able to find food.
Birds become stressed, lack energy and naturally seek hiding
places where they will be safe from their natural predators but
will also be able to find enough food and water to survive.
Occasionally this may be near one’s home, but most birds tend to
remain away from feeders during their molt.
Molting usually replaces feathers in so-called
"waves" so that at no one time should there be bald
spots. Large wing and tail feathers are usually shed first,
followed by a progressive molt of body feathers from the rump to
the head. There is a very precise and balanced order of the
molting of the primary and secondary flight feathers, this to
ensure that the bird continues to have its vital powers of
flight.
It was during my approximately 25 years of banding songbirds
for the US Fish and Wildlife Service that I was able to observe
and capture a number of blue jays, along with a few cardinals,
that had totally bald heads. What terrible looking messes they
were. A few species, such as the turkey vulture, have bald
heads, but there are no bald-headed songbirds. Keep a close
watch at your feeders during the next several weeks and you too
might see a blue jay minus all of its head feathers.
At first glance most people would simply conclude that the
bald-headed bird is molting. Well, it turns out that in many of
these instances the head feather loss can be attributed to mite
infection whereby many of these tiny arthropods’ feeding on the
bird’s skin has destroyed its feather shafts. Unfortunately the
head is one place on a bird that is very difficult to impossible
for the bird to reach with its feet and to preen. Normally these
mites would be gotten rid of by preening. Nutritional deficiencies,
or a combination of causes, may also lead toward some
feather loss.
Brace yourselves for a decrease in the numbers of birds coming
to your feeders knowing, however, that they are in safe secluded
places growing new sets of feathers. It’s a simple matter for
people to go to a store to purchase a new set of clothing. Birds
have to grow their own!
This bedraggled-looking adult male cardinal is
undergoing its late-summer complete molt.
This column appeared in the Door County Advocate
on 08/14/2004.
© Copyright 2004 Roy Lukes. All rights reserved.
