4.3.2Cage traps
These range from the simple cage propped up on a broken stick (drop trap),
which is knocked out the way by a bird, through a variety of cages which the bird
must enter for food, thereby tripping a door-release mechanism (either on the
floor, for example Potter trap, or roof, for example Chardonneret trap), to large
permanent cage traps such as the crow trap (an aviary-sized cage with a mesh fun-
nel set downwards in the roof ) or Helgoland trap—a huge horizontal mesh funnel
set in an area with little vegetation or cover and planted inside (typically with
some hardy berry-bearing shrubs to provide food as well as shelter) to attract
birds, which must be driven by the trapper toward a clear-fronted catching box
(which the bird sees as a way out).
In the case of wader traps (e.g. wader funnel trap, Ottenby trap, wader nest
traps), rail traps, and Helgoland traps, birds simply walk or fly through the trap
entrance and can continue to feed within the trap. Walk-in traps, which can be
used to trap waders at the nest (but replace the clutch with dummy eggs, so keep-
ing the real eggs safe and warm), are typically less than about 1 m^3 , while
Helgoland traps, which are typically built at coastal observatory sites, can be up
to a hectare in extent. In some of these traps, the birds might not realize that they
are trapped until the researcher arrives. Such “passive” traps are benign for this
reason. Large traps such as Helgolands also have a side door through which the
trapper leaves the trap after the birds are caught. This is also useful to deactivate
the trap when nobody is available to work it. Trap deactivation is valuable also for
pre-baiting. With any form of trapping (or netting) where birds must be concen-
trated near the trap site, or where neophobia would prevent the bird from entering
the trap (trap-shyness), it is essential to set the trap for a few days with food inside
so that the bird can enter and leaveat will, to gain confidence. Larger cage traps
offer the opportunity to include shelter within the trap so that operation may be
continued in poor weather.
4.3.3Spring traps
Unlike cage traps, which can be active or passive, spring traps are always active,
and consist of some sort of spring-loaded mechanism to close off an entrance,
through which the bird must pass to reach bait. Because of the spring loading,
great care must be exercised in their setting, and rapid extraction of the bird is
important. Also, unlike some cage traps, spring traps catch only one of several
birds at a time, and many traps might be set at once if capture-frequency and
processing-time permit. A very effective spring-trap is the bow-net, which con-
sists of a circle of netting (e.g. 30–50 cm radius) held flat open on the ground by
90 |Birds in the hand