a wire mechanism. A bird (ground foragers, robins, chats, wheatears) is attracted
by a bait such as a live mealworm tethered at the center of the circle of net. To take
the bait, the bird must be well within the circle of net, and on taking the bait the
mechanism is closed by a mousetrap spring so that the bird is caught within
a semi-circular sandwich of netting. The trap must also be pegged down so that
it cannot be moved (e.g. by the bird inside).
4.3.4A couple of nestbox traps
A useful passive trap for catching parent birds (tits, flycatchers etc.) in their nestbox
consists simply of an inverted “U”-shaped piece of wire pinned lightly (so that it
is free to move) to the inside of the box just above the entrance hole so that the
“arms” of the “U” hang down over the inside of the hole. Thus the birds can enter
by pushing the wire out the way (which they will do) but not escape when the
wire falls back down behind them. Note that unless the bird shows at the
entrance, there is nothing to alert the researcher to the bird having been caught,
and both parents can enter the box without the trap having to be reset. Because
this trap is difficult to use in woodcrete boxes, researchers at the Edward Grey
Institute (EGI) designed a spring trap to close a light metal door behind a bird
after it had entered. It consists of a metal plate with a hole larger than, but corres-
ponding to, the entrance hole on front of the box. The sliding door holds a flat
steel spring in compression when open and the door is held open by one end of
a pivoted perch that the bird depresses on entering the box, so releasing the
mechanism and closing the door. Such traps must not be used until the brood is
at least half-grown because disturbance during laying or incubation may cause
many species to desert.
4.3.5Noose-carpet traps
In circumstances where a bird returns to a particular spot, such as its nest, a
carpet of monofilament nooses can be used to trap adult birds. A large number
(50) of loose nooses are tied to a circular wire frame large enough to encircle
the nest cup and its contents. The frame must be secured so that the bird cannot
fly off with it. The nooses are arranged to sit over the nest-contents so that when
the bird settles to incubate, it unknowingly catches its feet in the nooses. Upon
the researcher’s approach the bird leaves hastily, and, if set properly, will be
caught by a monofilament noose holding the leg. Since capture occurs on your
approach, the birds should not be caught for long. Nevertheless, birds can be
highly agitated by this and so, as with any trap set over the nest during incuba-
tion, it is essential that eggs are replaced by dummies prior to using this trap, and
be sure not to allow the real eggs to chill while in your care. Noose carpets work
Catching the birds| 91