Where their ranges overlap, crows severely impact the annual waterfowl populations. When the hens begin laying, crows break open and eat the eggs. Later they will return and devour the fledglings. In the 40's a biological survey was conducted that really shows the damage crows can cause to the waterfowl in the Canadian "Duck Factory". It was shown that crows in close proximity to duck nesting areas took an average of 110 to 120 eggs or fledglings per crow per year, approximately 20,000,000 ducks. During the same year, sportsman only took 11,000,000 ducks. A common slogan of the time was "Kill a crow, Save a duck". At a time when waterfowl seasons are being dramatically reduced and even canceled, the survival rate of waterfowl at their breeding grounds is paramount. Shooting crows can make a real difference. Crows also take a heavy toll on upland game birds, including direct responsibility for at least 4 1/2 percent nest depredation on ruffed grouse and in California crows have been implicated in the endangerment of the Mojave desert tortoise. They also prey on small mammals such as rabbits and squirrels and have been known to kill prey as large as newborn lambs.