appeared to be more effective than shell 
crackers, since they left a trail of smoke 
or sparks (89). 
Shell crackers have been widely used and 
are considered effective for flushing starlings 
if used regularly or in combination with other 
devices (156). Shell crackers also reduced 
numbers of herring gulls (Larus argentatus) 
feeding at garbage dumps in New England. 
Gulls were repelled from a dump at Chatham, 
Mass., for 8 days and from a dump at 
Portsmouth, N.H., for 6 days (81). 
At some airports, bird problems have been 
alleviated by "shotgun patrols.'' Using both 
regular ammunition and shell crackers, patrol 
personnel fire upon nuisance birds. This 
system has worked particularly well at Logan 
International Airport, Boston, Mass. Several 
manufacturers in the United States are de- 
veloping reliable, long-range (200 yards) shell 
crackers. Patrolling with noisemaking devices 
is one of the few effective methods, and the 
use of shell crackers is being encouraged, 
as well as the development of better types of 
ammunition. 
Carbide or acetylene exploders have been 
used for bird dispersal for many years. These 
devices have been employed with varying de- 
grees of effectiveness in fields of rice, corn, 
and grain to repel ducks, geese, and black- 
birds (100). Carbide exploders in a small 
grain area in Saskatchewan reduced duck 
damage without spreading the losses among 
other farmers (130). Acetylene exploders and 
rope firecrackers were used to repel red- 
winged blackbirds from a Delaware cornfield 
during the 1961 damage season (93). Signif- 
icantly less damage occurred when the scare 
devices were used, and the exploders were 
superior to the rope firecrackers. 
In tests comparing exploders with broadcast 
alarm calls to repel red-winged blackbirds 
from an Ohio cornfield, both devices, operated 
on alternate days, offered significant protec- 
tion (92). The exploder was effective to a 
distance of 600 feet. In California, two carbide 
exploders were used successfully to repel an 
estimated 5,000 starlings from two adjacent 
5- and 20-acre fig orchards (156). No star- 
lings fed in the orchards for the remaining 
18 days of the experiment. 
Carbide exploders also are used in France 
against Corvidae and other birds, but their 
186 
effectiveness generally lasts only 2 to 6 days 
(124). 
Rifles and shotguns are used widely against 
nuisance birds, both as lethal agents and as 
scaring devices. The .22-caliber rifle was 
reported as the best single weapon known for 
frightening blackbirds from open ricefields 
(100). Larger caliber rifles also are effective, 
but ammunition cost is considerably higher. 
The shotgun, although often used, was reported 
to be one of the most ineffective weapons 
against blackbirds attacking ricefields (100). 
Shotguns are used a great deal in England. 
They are believed to have little effect on 
bird numbers, but are effective as a scaring 
method (124). Shotguns used with other sound 
sources are also important devices for dis- 
persing starlings from roosts in England (19), 
Germany (122), and Switzerland (99). With 
the advent of shell crackers, the shotgun also 
has become very uSeful, particularly at air- 
ports, where shotguns are considered safer 
than rifles. 
In recent years, research workers have 
investigated the potential of ultrasonics, air 
horns, and broadcasts of recorded calls. 
Many individuals have expressed the idea that 
nuisance birds might be controlled with ultra- 
sonics. The upper audible limit for birds is 
about the same as that of man, however (58); 
and hence ultrasonics offers little at this 
tire for use in bird control. 
Air horns effectively deterred starlings from 
feeding in a California vineyard. The horns 
were battery operated, and the rate of opera- 
tion was automatically timed. Five horns, 
operated from 6:30 a.m. to 6:30 p.m. daily, 
were used to protect 57 acres of grapes for 
7 days (156). 
Frings and his coworkers have developed 
a relatively new and unique approach to the 
control of pest birds. The method employs 
recorded communication signals of birds to 
affect their movements. Starlings were chased 
from tree roosts by broadcasting a recording 
of what is now commonly called the distress 
call (55). Herring gulls were successfully 
repelled from feeding sites and attracted to 
other feed by using both alarm calls and feed- 
ing calls (54). Recorded calls of the eastern 
crow (Corvus brachyrhynchos) were also used 
to study reactions to broadcasts of assembly 
and alarm calls (53). Frings et al. concluded 
