For years, Bio-Diversity
Products has recommended the practice of cleaning
nest boxes annually, usually in the late fall, as preparation for
the coming nesting season. We have felt that this practice
maintains the integrity of the box. At the same time, inspections
may uncover situations that may prevent repeated inhabitancy,
such as colonies of wasps, or conditions that might affect the
chicks, such as lice infested debris. However, with the risks
related to hantavirus coming into view, we feel that our
customers might want to re-evaluate this practice, or at least
become aware of the problem.
Hantavirus is a danger whenever a person comes
into contact with wild rodents. This is most particularly true
about deer mice, a species known to be the hantavirus's main
vector. The deer mouse is common across much of the United States
and is easily identified by their white undersides. While the
deer mouse carries the virus without showing signs of being
infected, it can contaminate almost everything it comes into
contact with. Exposure to this deadly disease can come from the
rodent's hair, their fecal matter or their nesting material.
Since 1993, 138 case of hantavirus have been
diagnose in Arizona, Colorado, New Mexico, Idaho and Oregon. 23
people have died as a result of contact with the virus. No cases
to date have been recorded in California.
Hantavirus is a concern for growers who use nest
boxes to attract barn owls. Barn owls cough up castings, or owl
pellets, that contain the undigested hair and bones of their
prey. Many casting can be found in an occupied nest box. As well,
uneaten rodents may also be found in nest boxes. Debris in an owl
nest box can potentially be infected.
While cleaning out nest boxes at least once a year
may still be beneficial as far as the owls are concerned, this
act can expose a person to hantavirus. Certainly, the benefits of
having a clean nest box are hardly worth the risks of exposure to
this grave illness. However, if a nest box is to be cleaned, the
person must use rubber gloves and a dust mask. The debris from
the nest box should be contained in a sturdy plastic bag and
disposed of. Every effort should be made to stay out of the dust.
for more information about the hantavirus and the disease it
causes, the Hantavirus Pulmonary Syndrome, please consult the
following webistes.
New World
hantavirus and Hantavirus Pulmonary Syndrome
Outbreak
- Hantavirus Pulmonary Syndrome and Hemorrhagic Fever with Renal
Syndrome
All
About Hantavirus
W W W . H A N T A V I R U
S . N E T
Our customers comment...
Coping with
the GHO
Joe
Sebastiani, property manager of of Viansa Winery, reports that
great horned owls, GHO's, have been seen perching on either the
roofs or landing perches of the 18 barn owl nest boxes his
operation has purchased from Bio-Diversity Products.
To reduce the threat of GHO's attacking young inside or outside
the nest boxes, Sebastiani has removed the exterior portion of
the dowel from the box.
While the farmer admits that no one has actually
seen these predators invading the interior of the nest boxes, he
hopes these measures will reduce the slaughter of his gopher
eating allies.
It is estimated that as much as 50% of all barn
owl deaths may be attributed to predation by the great horned
owl. One way to avoid exposing the barn owl to the wrath of the
GHO is to place nest boxes at least a half mile away from areas
recognized as great horn habitat, such as riparian corridors or
densely wooded areas.
Sebastiani states that this would be very
difficult in his situation. Located at the mouth of the Carneros
Valley near Suisun Bay, the heavily wooded hillsides are perfect
for the great horn.
"Great horns are everywhere," he says.
"There is no way we could avoid over lapping the hunting
grounds of the two species."
For now, he notes, it doesn't seem to be stopping
the barn owls from doing their job. All of Viansa's nest boxes
show signs of occupancy. Ironically, the two enemies even seem to
get along at times. "We have observed great horns and barn
owls roosting in the same tree," adds Joe.
Bio-Diversity's design,
with an entrance of less than 6 inches in diameter and an
interior partition, is intended to keep predators, like the GHO,
out of the interior of the nest boxes. However effective as these
components are, they will not help an unwary chick, perched on
the dowel outside of the box, from a swift, stealthy attack.
For now, Sebastiani is playing it safe. Removal of
the landing perch has not reduced the occupancy of the nest boxes
since the adult barn owl does not need the dowel to enter and
exit. However, Viansa's action may help reduce predation of the
young, who use the exterior portion of the perch to exercise
their wings before attempting their first flight.
Bio-Diversity Products
commends Joe and the others at Viansa for taking this action and
recommends that others do the same where pressure from the GHO is
a concern. We also recommend shortening the fledgling flight by
locating nest boxes within 100 yards or closer to trees. This
will reduce the chicks' need for preparation.
Once in the relative safety of the trees, the
chicks continue to be nurtured by their parents for several weeks
more, while gaining strength and survival skills.
Finding the
Balance................ by Tom Hoffman
Since
I began promoting the use of barn owls for rodent control, I've
spoken with many growers about their successes and failures with
this program. I've noticed that those who have a positive story
to tell, have one thing in common. They have achieved a natural
balance between predators and prey. So what is it that these
farmers are doing that others aren't?
The answer lies in the numbers. When attempting to
control rodents with barn owls, the biggest mistake you can make
is to not provide enough nesting sites. You have to take
advantage of one of the unique characteristics of the barn owl:
its lack of a sense of territoriality. Where the food source will
permit, barn owls will live in what appear to be colonies. That
is what makes the barn owl an effective ally. And the
right approach is not to attract one or two pairs, but a whole
colony of them!
So at this point, the obvious question is: how
many nest boxes is enough? And the answer is: that
depends. For example, in placing my boxes in my own
vineyard, I tend to situate the boxes around the rodent infested
areas, figuring about four to six will handle 50 acres, and in
most years, most of them are used. In someone else's vineyard,
where rodents are not such a serious problem, the same number of
boxes might work for 100 acres. What ever the number is
in your field, your goal should be to allow as many nesting pairs
of owls to move in as your rodent supply will sustain, then
permit them to find a balance with the food supply.
To determine when that balance has been reached,
look at your occupied nesting sites, counting only the boxes with
nests in them. (Solitary roosting adults don't count.) If the
occupancy rate is 50 to 80%, then figure the balance has been
reached and you probably don't have food for too many more
nesting pairs. And when the gopher population increases, you'll
still have room to accommodate more owls.
On the other hand, if you continually have close
to 90 or 100% occupancy, you could probably use more nest sites.
I say probably, because you will never know unless you
actually put the boxes up and see if the owls move in or not.
Remember, year by year, the owl population will
reflect the rodent population, each fluctuating in response to
the density of the other. With a high rodent population, you will
be able to sustain more owls and they will remain in until the
food supply begins to dwindle. Then the owls will disperse to
greener pastures. With fewer owls on duty, the gophers are once
again on the rise.
This newsletter was published for the
customers of Bio-Diversity Products.
For more information about our products or services, contact us
at (209)369-8578, or email us at: thoffman@lodinet.com.
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