Vancouver Naturalist_March 2012.pdf - Nature Vancouver

Conservation Matters
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hired consultant Gary Searing of Airport Wildlife Management
International to develop and implement this program. Since then,
40 raptors have been trapped and moved away from the airport:
35 Red-tailed Hawks, 3 Rough-legged Hawks, and 2 Snowy Owls.
Most of these were caught in a bal-chatri trap, which consists of a
cage with a conspicuously visible (but protected) live rodent and
a series of monofilament (invisible) nooses that snag the legs of
the raptor as it attempts to take the bait. Gary found that he had to
keep a close eye on the baited trap because Bald Eagles will arrive
very quickly to grab the snagged raptor. White tags with prominent
numbers are placed on the wings of captured birds – right wing of
a female and left wing of a male. The raptors are then handed over
to OWL (Orphaned Wildlife Rehabilitation Society in Delta) for
a health check, banding, and deportation to the Chilliwack area,
where they are released.
Seventeen of the relocated Red-tails have returned to YVR. Of
these, 14 are known to be residents of Sea Island or regular winter
visitors. These older birds have learned to avoid aircraft, so are
not re-trapped but allowed to stay – although they are closely
watched. Three of the returning birds were transients, while 18 of
the relocated Red-tails have not been seen again. In general, young
hawks and the transients do pose a hazard and are (re)trapped.
Northern Harriers and most owls (Barn, Short-eared) are wary of
traps and none have been caught. Unfortunately, Barn Owls are
frequent strike victims – one per month on average.
Tour of the Airfield At the wildlife control field station, we
were shown the bal-chatri trap and various other devices used
to handle, tag, and care for the raptors during their short-term in
captivity. Out on the airfield we viewed a Swedish Goshawk trap,
designed to catch large raptors. This is a large cage with doors that
close when a heavy bird lands on a central perch. Large raptors are
attracted to the vicinity of this trap by flurries of starlings held in
an adjacent wire-mesh enclosure (with food and roosting cavities
supplied), and a live pigeon in placed in a separate compartment
beneath the trap itself.
Measures being taken make airfield habitat less attractive to large
birds include covering (i.e., culverting) ditches to avoid attracting
ducks and herons, and installing arrays of shiny streamers that
flap in the wind also along ditches. Maintaining the best possible
drainage of the grassy areas is also important because standing
water will attract ducks.
On the outer dyke we met a wildlife controller who demonstrated
some of the arsenal of firecrackers – bangers, screamers and twisters
– that are used to harass (frighten away) potentially hazardous
flocks of birds. Live ammunition is used only as a last resort. Also
effective is a powerful light beam that is used to “herd” flocks
of Snow Geese away from the vicinity of airport runways. The
wildlife control team includes two Border Collies; we met one,
with his handler.
At present, falconry is being tested as a means of wildlife control;
last year there were two successful trials. Falcons have been used
previously at YVR to evict unwanted birds, such as pigeons, from
aircraft hangers. Now they may be used to disperse potentially
hazardous birds, such as the hundreds of Dunlin that forage and
loaf in the intertidal areas, but move onto the airfield and runways
during high tides and during stormy weather. When a falcon is
flown in a straight line from one handler to another, Dunlin flee the
raptor’s flight path. (The falcon is trained not to pursue individual
birds since a chase could end up in the path of an aircraft.) Further
trials are planned.
Other aspects of wildlife control mentioned only briefly during the
course of the morning included: the new security fence, designed
to keep out coyotes so it extends well below ground level; when
a strike occurs, there is a requirement for runway closure until the
remains of the bird or animal are found and removed; the problems
of trying to manage the voles and mice that attract the raptors to
the airfield; and control policies for geese and herons.
It was a morning very well spent. We learned much about YVR’s
wildlife management program and gained insight into the difficulties
and heavy responsibilities faced by the wildlife technicians as they
do their best to avoid unnecessary culling of birds while maintaining
the safety of aircraft and the travelling public. Many thanks to
Simon Robinson, Gary Searing, Dave Ball and the other wildlife
technicians who spent the morning with us.
Nature Vancouver members attending: Daniel Overmyer, Margaret
Coutts, Bev Ramey, Jeremy McCall, Richard Swanston and June
Ryder.
If you see raptor with a large white wing tag, record the number on
the wing tag if possible, the wing (right or left) that is tagged, time
and location of the sighting, and send to gfd@airportwildlife.ca.
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