There are other interesting details in Cooke’s account to which the reader is referred.
During migration the parula warbler does not frequent haunts typical of its breeding ground; in fact such are not to be found in much of the country over which it travels; nor does it especially frequent the coniferous woods to which it is partial in summer. It is to be found almost anywhere, in many kinds of trees, though it seems to show a decided preference for deciduous woods. There, it may often be seen drifting through the highest tree-tops in mixed groups of migrating wood warblers, gleaning insects amidst the freshly opening foliage. Referring to the Buckeye Lake region in Ohio, Milton B. Trautman (1940) writes: “The transient Parula Warblers usually displayed a preference for large pin oak and shingle oak trees and a marked preference for one shingle oak in particular. This oak was in the Lakeside Woods, and more Parula Warblers were observed in it than in all of the remaining trees of the woodland. A transient often displays a marked preference for certain types of trees, but it appears unusual for a single tree among many of the same kind to retain yearly so marked an attraction for a particular bird species.”
The migrating parula warbler is often seen in roadside trees and in shade trees in parks and gardens. It even visits our orchards, where one of the most charming sights of springtime is to see this gay-colored, tiny warbler flitting about in search of insects among the apple blossoms, a delightful bit of color contrast in a beautiful setting.
Nesting.—The nests of the northern parula warbler that we used to find in southern Massachusetts were all located in haunts similar to those described, and mostly in old orchards heavily festooned with beard moss (Usnea). We could usually find three to five nests in a well-populated orchard, but they were so well hidden in the hanging moss that we may have overlooked some. A casual observer would never notice one, but with practice we learned to recognize a rounded, cuplike, thick place in a bunch of Usnea as indicating a nest. The nests were usually made in bunches of moss that hung from horizontal or sloping branches and were from 5 to 15 feet above the ground, more being below than above 12 feet. Some nests were in red cedars, or savins (Juniperus virginiana), scattered among other trees or growing in open stands by themselves; they were located in bunches of Usnea close to the center of the tree and often within reach from the ground. Occasionally, isolated trees on the edges of swamps or on the shores of ponds were sufficiently covered with the lichen to contain nests, and these were sometimes as much as 20 feet above the ground. The nearest approach to a colony that I ever found was in a small cedar swamp, not over an acre in extent, that jutted out from the shore of a lake into rather deep water.
The white cedars (Chamaecyparis thuyoides) were growing in water that was waist deep or more in places, and the whole place was so obstructed with fallen trees and sunken snags that it was very difficult to explore thoroughly; I managed to find some half a dozen nests, and there may have been others, for many of the trees were well “bearded.”
The nests that we have found have all been very simple affairs, apparently merely pockets hollowed out in bunches of hanging Usnea, with side entrances slightly above the cups. Some nests were small and suspended only 2 or 3 inches below the supporting branch, practically open baskets accessible from directly above; others were found in long, thick bunches, a foot or more in length, with long streamers hanging below the nest. External measurements were therefore quite variable. Many of the nests were unlined, save with a soft bed of fine shreds of Usnea, some were scantily lined with a few pieces of fine grass, two or three pine needles, one or two horsehairs, or a few bits of buff-colored down from the stems of ferns; rarely, a nest was more elaborately lined with the latter material but never as profusely as are the nests of other wood warblers.
Apparently the nests were also difficult to find in Connecticut; “J. M. W.” (C. L. Rawson, 1888), who has probably taken more eggs of the blue yellow-backed warbler than any other man, says that the older ornithologists did not realize “that the three Southern New England States were about the centre of its breeding range,” until he began sending eggs to Dr. T. M. Brewer. Thomas Nuttall (1833) remarked: “The nest and eggs are yet unknown.”
Rawson found the parula warbler nesting in colonies near Norwich, Conn., and says:
I know a swamp where may be found seventy-five pairs of these summer residents. The first time I visited the Preston colony on the 31st of May, I took eight sets of four. The first time I visited another large community in this county on June 5, on a point of land trending into salt water, I took eleven sets of four. * * *