“Remember it's a sin to kill a mockingbird.” That was the only time I ever heard Atticus say it was a sin to do something, and I asked Miss Maudie about it. “Your father's right,” she said. “Mockingbirds don't do one thing but make music for us to enjoy . . . but sing their hearts out for us. That's why it's a sin to kill a mockingbird.” From "To Kill A Mockingbird" by Harper Lee
Of course, Atticus Finch was trying to teach his children a valuable lesson, to be kind to creatures and people who are harming noone. But as for that wonderfully flowery quote, anybody who gardens knows that it is absolute nonsense... Mockingbirds, despite their wonderful trills, are also one of the most annoying creatures on the face of the earth. They seem to take particular delight in pecking a small hole in each and every tomato on the vine, then moving on to do the same to the peaches on the tree.
As for the sin aspect... I make no moral judgements and would not presume to tell anyone what is or isn't a sin, but here in Texas, it is illegal. They are our state bird. They weren't made the state bird for their song though, they were made state bird for their ferocious temperament, namely, the willingness to defend their home territory against any attacker, no matter the size or odds of winning the battle.
And they will attack, dive bombing cats, dogs and people who come too near their nests.
I caught this guy sitting on top of a shrub, practising his mating calls, and he sang continuously for 6 minutes before taking a snack break, and then starting in again. He may be starting to establish a territory, but it's too early for the actual mating season... when that starts his song will be accompanied by acrobatic jumps about 3 feet in the air, flashing the white patches under his wings to let any other birds in the area know that this is his turf and they'd be well advised to stay clear. It's also accompanied by fits of avian insomnia and all night singing. Take my word for it, the song that is so wonderful outside the dining room window when your having your morning coffee is absolutely unnerving at midnight outside your bedroom window.
All this would be fine for a couple of weeks in the spring, but here in Texas, they raise at least 2 clutches of eggs a summer, usually 3 but sometimes 4, each and every clutch preceeded by a fit of incessant warbling. But, we live with them.