2 LEAFLET 120, U. S. DEPT. OF AGRICULTURE 
or edges. Vertical wires sticking out of apexes and a series of 
them at short intervals on ridges will prevent perching. In the 
case of structures not originally bird-proofed, cement can be used to 
close, or wire mesh to cover, the openings and offsets frequented by 
birds. | 
Excluding birds from the water is a different problem, but on 
small reservoirs, at least, it has been solved. The successful measure, 
devised after trial of various others, is the installation of a system 
of criss-crossed, widely spaced wires covering the entire water sur- 
face (see illustration on title page). Apparently this system was 
devised in Victoria, British Columbia, and it has been copied with 
satisfaction in several cities of the Pacific Coast States. The experi- 
ence of G. W. Pracy, superintendent of the city water-distribution 
department of San Francisco, is summarized (1927) in the following 
quotation : 
We... tried this on one of our reservoirs measuring about 200 feet square, 
stringing the wires 40 feet apart in both directions and found it was entirely 
successful in keeping the seagulls away. ; 
We next strung similar sets of wires over a larger reservoir, being circular 
in form and about 400 feet in diameter. This also being successful, we pro- 
ceeded to string wires over our largest reservoir which is irregularly Shaped, 
but about 1,000 feet long by 600 feet wide. In the first two reservoirs, we used 
the ordinary no. 9 galvanized iron wire, commonly known as telephone wire. 
These were fastened to 2-inch pipe driven into the ground. On the large reser- 
voir, we felt that wires of this size would not stand the strain necessary to 
keep them taut over so large a span, So we first installed a system of larger 
cables, one-fourth and one-half inch in diameter, using these to support the 
small wires. Two pipe supports resting on the bottom of the reservoir and 
spaced about one-third of the way across were used to shorten the span. 
A system would have to be worked out in detail for each size and shape of 
reservoir, but in our case it was comparatively simple and worked perfectly. 
The wires are pulled taut, the network of wires being about 1 foot above the - 
high-water mark in the low part of the span. 
The small reservoirs cost us about $50 for the complete job; the large reser- 
voir cost about $400. The results have been entirely satisfactory. We get an 
occasional seagull, but they appear rarely and they do not stay. 
Gulls, the birds most frequently complained of as polluting reser- 
. ) uv . . =) 
volrs, apparently are deterred from alighting on water areas pro- 
tected by a simple network of wires. They will walk into a reservoir 
if there is a favorable margin, but are stopped by a single strand of 
wire strung about the edge at a height of 6 inches. In attempting to 
pass this barrier they take to their wings and when in flight appar- 
ently fear to try to penetrate the covering network. Occasionally 
individual gulls learn to alight on the water despite the wires, and 
these must be scared off, as they will attract others. Occasionally 
gulls have been reported as settling on a reservoir having wires 30 
feet apart, but never as visiting one where the spacing was 20 by 
22 feet. Gulls also decoy to coots or ducks that, undeterred by the 
wiring, may alight on a reservoir. 
These waterfowl are more difficult to exclude, but where trouble- 
some they may be controlled in part by the erection of a wire-mesh 
fence (18 to 36 inches high) all around the margin to prevent their 
walking in. Having wide shores of gravel or of concrete rather than 
of grass and keeping the reservoir free of aquatic vegetation also 
will tend to discourage the visits of these birds. Deep reservoirs are 
less adapted to plant growth than are shallow ones. The experiment 
