Part 10

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, 13-1/2, 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 10-3/4 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 or river, stretches back among the trees. Here he loves to hop about on floating drift-wood, wet by the lapping of pulsating wavelets; now following up some long, inclining, half-submerged log, peeping into every crevice and occasionally dragging forth from its concealment a spider or small beetle, turning alternately his bright yellow breast and olive back towards the light; now jetting his beautiful tail or quivering his wings tremulously, he darts off into some thicket in response to a call from his mate; or, flying to a neighboring tree-trunk, clings for a moment against the mossy bole to pipe his little strain or look up the exact whereabouts of some suspected insect prize.

Voice.--The same gifted writer and careful observer (Brewster, 1878) gives the following good account of the distinctive song of this warbler:

The usual song of the Prothonotary Warbler sounds at a distance like the call of the Solitary Sandpiper, with a syllable or two added,--a simple peet, tweet, tweet, tweet, given on the same key throughout. Often when the notes came from the farther shore of a river or pond we were completely deceived. On more than one occasion, when a good opportunity for comparison was offered by the actual presence of both birds at the same time, we found that at the distance of several hundred yards their notes were absolutely undistinguishable; nearer at hand, however, the resemblance is lost, and a ringing, penetrating quality becomes apparent in the Warbler's song. It now sounds like peet, tsweet, tsweet, tsweet, or sometimes tweet, tr-sweet, tr-sweet, tr-sweet. When the bird sings within a few yards the sound is almost startling in its intensity, and the listener feels inclined to stop his ears. The male is a fitful singer, and is quite as apt to be heard in the hot noontide or on cloudy days, when other birds are silent, as during the cool morning and evening hours. The ordinary note of alarm or distress is a sharp one, so nearly like that of the Large-billed Water Thrush (Siurus motacilla) that the slight difference can only be detected by a critical ear. When the sexes meet a soft tchip of recognition common to nearly all the Warblers is used. In addition to the song above described the male has a different and far sweeter one, which is reserved for select occasions,--an outpouring of the bird's most tender feelings, intended for the ears of his mate alone, like the rare evening warble of the Oven-Bird (Siurus auricapillus). It is apparently uttered only while on the wing.

Although so low and feeble as to be inaudible many rods away, it is very sweet, resembling somewhat the song of the Canary, given in an undertone, with trills or "water-notes" interspersed. The flight during its delivery is very different from that at all other times. The bird progresses slowly, with a trembling, fluttering motion, its head raised and tail expanded. This song was heard most frequently after incubation had begun.

Dr. Roberts (1936) refers to this flight song, as delivered "after the manner of the Maryland Yellow-throat, * * * consisting first of the usual rapid monotone of five or six notes and ending with a pleasing, varied warble, full and strong in some of its notes and far sweeter than the usual utterance."

Dr. Walkinshaw (1938) says of the usual song: "Uttered at the rate of five or six times per minute, the song lasts slightly over one second. It is given all day long from the time of arrival until the young have left the nest and has been heard as late as the 16th of August (1931). The frequency is much greater during the early nesting season and during the earlier hours. During midday on warmer days the number of times per hour seems much less. Later, from four until near sundown, it again increases. During late nesting, when the young are about to leave the nest, the rate again decreases, but it is heard several days after the young leave the nest." Aretas A. Saunders tells me that the songs are pitched at C´´´´ or B´´´, and the call note, tseek, at A´´´.

Field marks.--The golden swamp warbler could hardly be mistaken for anything else. The rich, brilliant yellow of the head and breast, sometimes almost orange on the head, only slightly paler in the female, the absence of wing bars, and the large amount of white in the tail will distinguish it.

Enemies.--Dr. Walkinshaw (1941) says that the house wren is a serious competitor with the prothonotary warbler in Michigan, contending with it for nesting sites in the bird-boxes.

The cowbird is a persistent enemy of this warbler in spite of its hole-nesting habits; perhaps if the warbler nested in deeper holes it might find some relief from this pest. Among 70 sets of eggs of this warbler in the J. P. Norris collection, 18 contain cowbirds' eggs. Dr. Friedmann (1929) found no less than 36 records of such parasitism in the literature, and says: "As many as four eggs of the Cowbird have been found in a single nest together with four of the Warbler's. There are several cases on record of doubled-storied nests of this bird, with a Cowbird's egg buried in the lower story. Such cases are, however, not common, and usually the Warbler seems to make no attempt to get rid of the strange eggs." E. M. S. Dale wrote to me of a nest, found near Toronto in 1933, that contained seven eggs of the cowbird and none at all of the warbler!

Snakes sometimes destroy the eggs or young.

Fall.--Dr. Walkinshaw (1938) says that "the majority of the Prothonotaries leave our rivers [Michigan] by the second or third of July. One may canoe some years a good many miles during the latter part of July or the early part of August without finding a single Prothonotary, whereas in other years many groups can be found. The majority evidently are early migrants. Very few remain until late August or early September, the latest date being September 9, 1934, at Battle Creek."

The 1931 A. O. U. Check-List states that this warbler apparently crosses the Gulf of Mexico in migration "and is not found in Mexico north of Campeche," but probably some migration is along the coast of Texas and Mexico, as suggested by George G. Williams (1945).