In Thoreau’s Walden, what are “tit-men”?

Dear Cecil: At one point in Walden, Henry David Thoreau, having grown bored with making the reader feel grubbily materialistic if he cannot carry all of his belongings on his back, moves on to rub the reader’s nose in his puny intellectual attainments: “I confess I do not make a very broad distinction between the illiterateness of my townsman who cannot read at all, and the illiterateness of him who has learned to read only what is for children and feeble intellects. We should be as good as the worthies of antiquity, but partly by first knowing how good they were. We are a race of tit-men, and soar but little higher in our intellectual flights than the columns of the daily paper.” Assuming Hank Dave was not channeling Russ Meyer or Howard Stern, what the devil did he mean by “tit-men”? The context suggests he meant men preoccupied by life’s inessentials — souls who lie in the gutter but fail to look up at the stars, or some such. Maybe he’s comparing us with birds. But as I can’t find the phrase in any old dictionaries I can’t be sure. Would you be good enough to shine the refulgent beacon of your nonesuch intelligence upon this umbrageous niche of Thoreauvia? David English, West Somerville, Massachusetts