supplemental feeding (birdfeeders) during the winter leads to greater nesting success (more baby birds) the following spring. Just make sure you use FRESH seed, not the junk sold in big box stores and such.
However, YOU could kill an owl just by using a poisonous/chemical rodent killer. Many brands of rodent poison aren’t finished when they kill a rodent; any creature that eats the rodent’s carcass (often an owl) is poisoned too. That’s a shame since an owl may kill and eat dozens of pests per day – at no cost or danger to you.