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UNITED STATES DEPARTMENT OF AGRICULTURE
MISCELLANEOUS CIRCULAR NO. 69

WASHINGTON, D. C. JUNE, 1926

CONSTRUCTION AND OPERATION OF BIOLOGICAL
SURVEY BEAVER TRAP

VERNON BAILEY, Biologist, Division of Biological Investigations me See

Bureau of Biological Survey binders

Tut BEAVER TRAP devised by the Biological Survey and
described in Department Bulletin No. 1078, ‘Beaver Habits,
Beaver Control, and Possibilities in Beaver Farming,” has been
greatly improved and strengthened until entirely satisfactory in
operation. The new trap (fig. 1) has been thoroughly tested, and in_
March, 1926, a patent was obtained for the writer by the Department
of Agriculture and dedicated to the use of the people of the United
States. It is designed chiefly for capturing beavers alive for control
and propagation, and can be manufactured by anyone for personal use
orforsale. Thespecifica-
tions and directions that
follow should enable any
machinist or practical me-
chanic to make the trap,
at a cost for materials,
in small lots, of about
$7, and for shop work
about $3.

B2937M; B2938M

Fig. 1.—Biclogical Survey cage trap for taking beavers alive. A, Trap held partly open to show con-
struction. B, Trap set and ready to be placed in the water. The trigger stands erect in the center of
the set trap 10 to 12 inches high, so that when struck on any side by a swimming beaver it releases
trigger bars and springs, and then the trap jaws close and lock above the captive animal. Details of
construction shown in Figure 2

MATERIALS REQUIRED

(Italic figures in parentheses show the part as illustrated in Figure 2)

1 cold-rolled steel bar 114 by 14 by 58 inches, for base bar (1).
2 cold-rolled steel bars each 7% by 33 by 8&7 inches, for trap jaws (5).
1 piece of flat iron 114 by 14 by 54 inches, for cross bar (2).

98480—26

2 MISCELLANEOUS CIRCULAR 69, U, S. DEPT. OF AGRICULTURE

1 piece of flat iron 1 by 14 by 18 inches, for top eross bar (3).

2 pieces of flat iron each 1 by 14 by 11 inches, for short cross bars (4).

2 pieces of strap brass each 34 by 7s by 6 inches, for clasping hooks (14).

2 pieces of No. 3! (14-inch) oil-tempered spring-steel wire, each 8 feet long, for
_ making the two coil springs (6).

1 piece of No. 6! oil-tempered spring-steel wire, 2 feet long, for trigger spring (8).

2 ae Oke 6 oil-tempered spring-steel wire, each 10 inches long, for trigger

ars :

SS Ze TP, fa B2936M
Fig. 2.—Details of construction of Biological Survey beaver trap
1. Base bar. 7. Trigger. 13. Trigger grip.
2. Cross bar. 8. Trigger spring, 14. Clasping hook.
3. Top cross bar. 9. Trigger wire. | 15. Wire mesh.
4. Short cross bar. 10. Trigger collar. | 16. Safety hook.
5. Trap jaw. 11. Trigger bar.
6. Coil spring. 12. Hinged trigger loop.

1 piece of 1-inch mesh, No. 16! woven wire, galvanized before weaving, 50 inches
long from a roll 60 inches wide, for bottom and sides of trap (15).

50 feet of No. 151 galvanized malleable wire, for lacing and linking wire mesh
sides and floor of trap to jaws and bottom, for making trigger wires (9),
trigger collar (10), and safety hooks (1/6), and for fastening trigger spring.

30 inches of No. 12 galvanized wire, for trigger (7).

5 quarter-inch bolts, four of them 34 inch long and one 1 inch long, for attaching
cross bars to base bar.

1 pair of 11%-inch brass hinges with strap-shaped sides, and two screw holes in
each, for trigger loop (12).

SHOP WORK

Drill ;4-inch holes as follows: Two side by side, 3 inches from each
end of base bar; and one 14 inch from each end of long cross bar.

Drill 14-inch holes as follows: One in center and one at 13 inches
from each end of base bar; one in center and one 6 inches each side
of center of main cross bar; one in center and one 4% inch from each
end of 13-inch cross bar; and one in center and one 14 inch from each
end of each 11-inch cross bar.

Drill =75-inch holes as follows: At 3-inch intervals along flat jaws,
lg inch from outer edge and to about 4 inches of the ends; one in
middle of one trap-jaw bar 10 inches to right of center and one in
the other 10 inches to left of center of trap; two in middle of main
cross bar at 8 and 9 inches from each end, for hinges for trigger loops.

1 All wire sizes are standard American gauge.

BIOLOGICAL SURVEY BEAVER TRAP 3

Heat and turn up ends of base bar at right angles, 5 inches from
ends, then heat and make a short quarter twist 2 inches from tips of
{urned-up ends, and thin the inner edge of twisted section to one-
eighth inch thick where it comes between trap jaws, to keep them
from passing the center.

Heat and turn up at right angles the ends of long cross bar, 2
inches from tips.

Heat and round and turn out at right angles 2-inch tips on each
end of the two flat steel bars for jaws, to fit the holes at the ends of
the base bar. In rounding the ends of the jaw strips the tapering
should be on the outer edge, so that the tips may be almost in line
with the inner edge.

Wrap No. 3 wire for coil springs 1214 times closely around a 14-
inch iron pipe or hardwood rod, leaving one end about 16 and the
other about 14 inches long, with the two ends at right angles when
open and free. The springs will unwind one full turn when released,
leaving 1144 turns. Heat and bend the tips of free ends of springs
to form hooks to clasp the jaws when crossed.

Bend the 24-inch No. 6 wire in form of hairpin, for the trigger
spring, about 10 inches long and 3 inches wide at the open end.

Bend 1-inch loop in one end of each of two 10-inch No. 6 wires,
for trigger bars.

ASSEMBLING THE PARTS

Bolt longest cross bar at right angles under base bar with the 138-
inch cross bar above, with a 1-inch bolt through center and two 34-
inch bolts through holes in ends of 13-inch bar and corresponding
holes in long cross bar.

Fasten the two 11-inch short cross bars across top of base bar,
with a 34-inch bolt through the middle of each and through the hole
8 inches from the upright ends, to support bottom of trap.

Slip coil spring over bent-up ends of base bar until below right-
angle bend, with shortest arm next to jaws.

Bend jaws in a depressed semicircle around wooden form so that
they will fit together when in place and reach just inside of bent-up
tips of cross bar when open.

Spring bent-up tips of jaws into holes in turned-up ends of base
bar, and make all necessary corrections of curving so that jaws will
fit together.

Clasp shorter end of spring on one jaw, and use pressure to bring
the longer end across to clasp the other jaw in an upright position.

Weave 3-inch half-hitch loops of No. 15 wire through holes drilled
3 inches apart in the trap jaws, the loops outward, and twist the
clasping parts down tight to jaws.

Hook the 1-inch loop at one end of each of the 10-inch No. 6 steel-
wire trigger bars downward into holes at ends of main cross bar, and
close up loops so they work freely.

Rivet the two small brass hinges at the holes 8 and 9 inches from
ends of main cross bars, so that the free ends will stand upright
about 7 inches from the turned-up ends of bars. A small hole
should be first punched or drilled near the middle of the free part
of each hinge, and the terminal screw hole enlarged to form a loop
that will admit the tip of the trigger bar loosely.

_ Make the trigger of No. 12 galvanized wire, bent in the middle
into a 2-inch circle, with downward projections one-fourth inch

4 MISCELLANEOUS CIRCULAR 69, U, S. DEPT, OF AGRICULTURE

below the circle to grip (73, in fig. 2) arms of spring and hold them
half closed, and with the two free arms standing erect, 11 inches
high, the ends looped to desired height. Pushing this trigger in any
direction lifts the downward projections (grips) of the circle, releases
the trigger spring, and springs the trap.

Trim the No. 16 woven wire for sides and bottom to fit inside of
arch of closed trap jaws and wire the bottom securely to top of base
bar at ends and middle and to ends of short cross bars. The inner
arm of spring should be thrust up through an opening in the mesh.

Wire closed end of trigger spring to wire mesh of floor of trap, in
line with base bar, the free ends extending 21% inches beyond center.
A wire loop or collar of No. 15 wire passed over both arms of trigger
spring near middle and under wire mesh will hold it in place and
prevent its opening too far.

Attach a No. 15 galvanized wire to each arm of the trigger spring
at center line of trap, making the two wires cross and reach to mid-
dle hole of hinged trigger loops on opposite sides of trap. Fasten
the ends of the crossed trigger wires connected with trigger spring
through the middle holes in the free part of the hinge so that when
the sides of the trigger spring are open the upright trigger loops will
not reach the tips of the trigger bars, and when the trigger spring is
held together by the trigger grips the loops will remain on the ends of
trigger bars to hold down the trap jaws.

Fasten upper edges of woven-wire side pieces to loops along trap
jaws, using No. 15 galvanized wire and lacing the edges together so
as to give flexibility to sides of trap.

Rivet a flat hook (4, in fig. 2) loosely on top of each trap jaw, in
the holes drilled 10 inches from middle of trap, facing the hooks oppo-
site ways, so that they will clasp the closed jaws and the trap can
not be opened from within.

OPERATING THE TRAP

Open trap jaws part way and place trigger on trigger spring to hold it half
closed and release tension on trigger loops.

Bring down one jaw and secure it in place by trigger bar and hinged trigger
loop, holding loop upright by a safety hook (16, in fig. 2) to keep trap from
springing. Repeat the operation with other jaw. =

Lift trap by base bar or cross bar underneath, and carry edge up to the water
where it is to be placed, or, if set from a boat, slide the trap over one side until
the lower edge rests on the bottom, then lower as boat is pushed back, leaving
the trap in desired position.

Release the safety hooks from trigger loops as last act when trap is satisfac-
torily placed.

Set trap in beaver canal, in creek or feeding place, or in front of landing place,
in water about a foot deep, either on the bottom or on stones or forked stakes or
cross bars, with tip of trigger about 2inches below surface of water. The trigger
can be bent over or straightened up to desired height for different depths of
water, varying from 10 to 16 inches.

Seatter aspen twigs back of trap, so that to get them the beaver will have to
swim against the trigger, thus springing the trap. The trap may also be sprung
by fastening one end of an aspen twig to the trigger and letting the other project
above the water so that the trigger will be moved when the twig is pulled by the
beaver.

A captive beaver can be carried to camp inside the trap, or in a gunny sack,
which can be slipped over the head and body while the animal is still in the trap.
Considerable time and patience are required to prevent frightening or exciting
trapped beavers, and all movements should be slow and quiet. Care must be
taken at first not to give the animals a chance to use their teeth, but as soon as
they get over being frightened they are easily handled.

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1926