It is most impressive when you first detect the presence of the bird by its shadow.

May 11.

A. M. —To Island. 

Only the lower limbs of bass begin to leaf yet, -- yesterday. 

A crow blackbird’s nest, about eight feet up a white maple over water, -- a large, loose nest without, some eight inches high, between a small twig and main trunk, composed of coarse bark shreds and dried last year’s grass, without mud; within deep and size of robin’s nest; with four pale-green eggs, streaked and blotched with black and brown. Took one. Young bird not begun to form. 

Hear and see yellow-throat vireo. 

See oat-seed spawn — a mass as big as fist —- on bottom; of brown jelly composed of smaller globules, each with a fish-like tadpole, color of a seed.

P. M. — To Andromeda Polifolia. 

Some young elms begin to leaf. Butternut leafs apparently to-morrow. Larger rock maples not yet begun to leaf, -- later considerably than large white maples, and somewhat than large red. 

Apparently andromeda will not open before the 15th or 16th, and the buck-bean, now just budded above the water, not before the 20th. 

Juniperus repens will not open, apparently, before the 14th or 15th. 

Canoe birch just sheds pollen. Very handsome drooping golden catkins, sometimes two or three together, some five and a quarter inches long. The leaves of some young sprouts already three-quarters inch over, but of the trees not started. 

The second amelanchier just sheds pollen, in a swamp. 

I trod on a large black snake, which, as soon as I stepped again, went off swiftly down the hill toward the swamp, with head erect like a racer. Looking closely, I found another left behind, partly concealed by the dry leaves. They were lying amid the leaves in this open wood east of Beck Stow’s, amid the sweet fem and huckleberry bushes. The remaining one ran out its tongue at me, and vibrated its tail swiftly, making quite a noise on the leaves; then darted forward, passed round an oak, and whipped itself straight down into a hole at its base one and a half inches over. After its head had entered, its tail was not long in following. 

You can hardly walk in a thick pine wood now, especially a swamp, but presently you will have a crow or two over your head, either silently flitting over, to spy what you would be at and if its nest is in danger, or angrily cawing. It is most impressive when, looking for their nests, you first detect the presence of the bird by its shadow. 

Was not that a bay-wing which I heard sing, — ah, twar twe twar, twit twit twit twit, twe?

Viola pedata sheds pollen,-- the first I have chanced to see. 

I hear some kind of owl partially hooting now at 4 P.M., I know not whether far off or near.

H. D. Thoreau, Journal, May 11, 1855

It is most impressive when, looking for their nests, you first detect the presence of the bird by its shadow. See September 16, 1852("I detect the transit of the first [hawk] by his shadow on the rock, and look toward the sun for him. Though he is made light beneath to conceal him, his shadow betrays him.")