scary image, cat drooling signify infection or food poisoning
.
I really don't know what to use to scare birds, they are quite intelligent and adapt quickly.
Some used polythene sheets to make noise ties to long pole (depends on wind),
some used shiny object like foil (don't you think, it will be like helipad on which bullseye is drawn in flashy lights),
some install gadgets to make loud noise periodically (birds don't pay much heed to after sometimes but neighbors will definitely start to scare you
),
some put sharp barbed wire,
keep cat/dog to scare the birds
Crows are more social than we think, instead of running away(flight) if one of them is harmed they tend to attack(fight) specially target head (so, don't forget to put on caps).