Don't have outdoor cats: https://abcbirds.org/program/cats-indoors/cats-and-birds/
From the cited source: https://www.nature.com/articles/ncomms2380
> We estimate that free-ranging domestic cats kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely __the single greatest source of anthropogenic mortality for US birds and mammals.__
(emphasis my own) Besides this, your cats will live longer and healthier. Like the average cat lives twice as long (or more) when indoor. Do it for the birds, do it for the squirrels and other small mammals, and do it for your own fucking cat.