to Kill a Mockingbird

Harper Leeの 'To Kill a Mockingbird' を読んでいます。 小説の題名となっている "to kill a mockingbird" が次の場面に出てきました。

When he gave us our air-rifles Atticus wouldn’t teach us to shoot. Uncle Jack instructed us in the rudiments thereof; he said Atticus wasn’t interested in guns. Atticus said to Jem one day, “I’d rather you shot at tin cans in the back yard, but I know you’ll go after birds. Shoot all the bluejays you want, if you can hit ’em, but 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. They don’t eat up people’s gardens, don’t nest in corncribs, they don’t do one thing but sing their hearts out for us. That's why it's a sin to kill a mockingbird.”

このセリフ "it’s a sin to kill a mockingbird" はこの小説の主題になっているのでしょうね。