Life Histories of North American Wood Warblers, Part One and Part Two. Arthur Cleveland Bent
The knees were farther under water earlier in the season. Most of his 76 Michigan nests were over water, or less than 100 feet from it; but 10 were 300 or more feet away from it and 2 were over 400 feet away. M. G. Vaiden tells me of a pair that nested in the tool box of a log-loading machine that was in daily operation, hauling logs.
Eggs.—From 3 to 8 eggs have been found in nests of the prothonotary warbler, from 4 to 6 seem to be the commonest numbers, 7 is a fairly common number, and at least 3 sets of 8 have been reported; in the J. P. Norris series of 70 sets are 34 sets of 6, 15 sets of 7, and 2 sets of 8.
The eggs vary in shape from ovate to short ovate, and they are more or less glossy. The eggs are undoubtedly the most striking of the warblers’ eggs, with their rich creamy, or rose-tinted cream, ground color, boldly and liberally spotted and blotched with “burnt umber,” “bay,” “chestnut brown,” and “auburn,” intermingled with spots and undertones of “light Payne’s gray,” “Rood’s lavender,” “violet-gray,” and “purplish gray.” There is quite a variation in the amount of markings, which are generally more or less evenly scattered over the entire egg; some are sparingly spotted and blotched, while others are so profusely marked as almost to obscure the ground color (Harris).
J. P. Norris (1890b), in his description of his 70 sets, describes 2 eggs in each of 2 sets as “unmarked, save for four or five indistinct specks of cinnamon.” These were in sets of 6 eggs each. Pure white, unmarked eggs were once taken by R. M. Barnes (1889). Dr. Walkinshaw (1938) gives the measurements of 78 eggs as averaging 18.47 by 14.55 millimeters; the eggs showing the four extremes measured 20 by 15, 19 by 16, and 17 by 13 millimeters.
Incubation.—The eggs are laid, usually one each day, very early in the morning; Dr. Walkinshaw (1941) says between 5:00 and 7:00 a. m. in Michigan; Meyer and Nevius (1943), in Tennessee, saw the female enter the nest to lay as early as 5:00 a. m. on May 2, and as early as 4:44 on May 23, remaining in the nest from 28 to 36 minutes on different occasions. The period of incubation is recorded as 12, 131⁄2, and 14 days by different observers; about 13 seems to be the average, according to Dr. Walkinshaw (MS.), probably depending on conditions and the method of reckoning. Incubation seems to be performed entirely by the female, but the male feeds her to some extent while she is on the nest. Incubation starts the day before the last egg is laid.
Young.—Meyer and Nevius (1943) write:
The adults shared feeding duties, and both removed fecal sacks. During the first three days the female steadily brooded the young. One female, observed from 4:55 to 8:10 a. m., when the young were one day old, spent a total of 70 minutes off and 155 minutes on the nest. Trips from the nest lasted an average of 8.6 minutes, while periods on the nest averaged 19.4 minutes. * * * At one nest when the young were eight days old, activities were noted during the eight and one-half hours from 8:30 a. m. to 5:30 p. m. The young were fed an average of 16 times an hour. * * * The adults were seen carrying spiders and insects, small green caterpillars frequently being used. Mr. H. P. Ijams saw a male offer a 10-day old nestling a may-fly. An incubator-hatched bird accepted egg-yolk, ants, ant larvae, crickets, earthworms, and spiders.
They say of the development of the young: “The young on the day of hatching had orange-red skin. The mouth lining was red. Down was distributed over the frontal and occipital areas of the capital tract, spinal tract, femoral, altar, and humeral tracts. Feather sheaths of the alar tracts penetrated the skin the first day after hatching. On the second day after hatching the eye-slits began to open. Feather sheaths of the humeral, femoral, and crural tracts emerged on the third day; those on the dorsal and ventral tracts emerged on the fourth day, and those of the capital and caudal tracts on the fifth day. On the fifth day the sheaths began breaking.” During the next five days the young developed rapidly and became more and more active, and on the tenth day began to leave the nest.
Young observed by Dr. Walkinshaw (1914) at Reelfoot Lake “averaged 11 days of age when leaving the nest in 1939, while 21 young in Michigan during 1939 and 1940 remained in the nest for a period of 103⁄4 days.” Of the comparative nesting success in the two localities, he says:
In Michigan from 1930 through 1940, 121 nests of the Prothonotary Warbler were observed. Only 28, or 23.14 per cent, were successful. Out of 413 eggs, 159 (38.47 per cent) hatched and 100 young were fledged (.87 per total nest; 3.78 per successful nest). The fledgling success was 25.66 per cent of eggs laid. More failures in Michigan resulted in more nestings by individual birds.
In Tennessee during 1939, 30 nests were observed until terminated or successful; 19 were successful (63.33 per cent) while out of 139 eggs, 78 hatched and all the young lived to leave the nest or 56.11 per cent fledging success of eggs laid; 2.6 young were fledged per total nest; 4.1 per successful nest.
He also notes that in Michigan the species is typically single-brooded if the first nesting is successful, but that in Tennessee it is typically double-brooded.
Plumages.—According to Dr. Dwight (1900) the natal down, located as indicated above, is brownish mouse-gray. Ridgway (1902) gives rather the best description of the juvenal plumage as follows: “Pileum, hindneck, back, and scapulars dull olive-greenish; wing-coverts, tertials, rump, and upper tail-coverts slate-gray, tinged with olive, the middle and greater wing-coverts narrowly tipped with light olive-greenish, producing two very indistinct bands; secondaries, primaries, and rectrices as in adults; sides of head pale yellowish olive; chin, throat, and chest dull light grayish olive, darkest on chest rest of under parts dull white, passing on sides and flanks into olive-grayish.”
In very young birds, according to Dr. Dwight, there is a variable amount of brownish wash on the back, which fades out to gray. And Dr. Chapman (1907) says that the white on the inner webs of the tail feathers is more restricted than in adults and more or less mottled with blackish. This first plumage is followed in June and July by a partial postjuvenal molt involving all the contour plumage and the wing coverts but not the rest of the wings or the tail. The young bird now becomes a golden swamp warbler, the young being nearly like the adults, the females being considerably duller in color than the males and having less white in the tail.
The crown and hind neck in both sexes, both old and young, are washed with dusky or olive in the fall. Spring plumages are produced by very slight wear without molt. There is one complete, annual molt in late summer.
Food.—Very little seems to have been recorded on the food of the prothonotary warbler. It is evidently highly insectivorous, obtaining most of its food from the trunks and branches of trees and shrubs and from fallen logs. Brewster (1878) says: “This Warbler usually seeks its food low down among thickets, moss-grown logs, or floating débris, and always about water. Sometimes it ascends tree-trunks for a little way like the Black-and-White Creeper, winding about with the same peculiar motion.”
Dr. Roberts (1936) lists “ants, and other insects and their larvae,” as its food. Some of the food of the young is mentioned above, most of which is doubtless included in the food of the adults. Spiders, beetles, may-flies, and other insects should be included, as well as many caterpillars and the larvae of water insects. Audubon (1841) says: “It often perches upon the rank grasses and water plants, in quest of minute molluscous animals which creep upon them, and which, together with small land snails, I have found in its stomach.”
Behavior.—Brewster (1878a) observes:
When seen among the upper branches, where it often goes to plume its feathers and sing in the warm sunshine, it almost invariably sits nearly motionless. Its flight is much like that of the Water-Thrush (either species), and is remarkably swift, firm, and decided. When crossing a broad stream it is slightly undulating, though always direct. * * *
In general activity and restlessness few birds equal the species under consideration. Not a nook or corner of his domain but is repeatedly visited through the day. Now he sings a few times from the top of some tall willow that leans out over the stream, sitting motionless among the yellowish foliage, fully aware, perhaps, of the protection afforded by its harmonizing tints. The next moment he descends to the cool shades beneath, where dark, coffee-colored water, the overflow of the pond