Why are domestic and feral house cats bad for birds?

Through the use of artificial selection, domestic house cats evolved from larger cats in a fairly short amount of time. This causes a major problem for birds, because the birds did not evolve with the pressure of having to avoid such predators. Thus birds, especially small birds, are ill-equipped to avoid being hunted by cats. It’s estimated that house cats kill approximately 3.7 BILLION birds word-wide each year.