Food.—The parula warbler is almost wholly insectivorous. Its food is mainly obtained in the deciduous trees, where it is often seen among the branches and twigs or hanging downward under a cluster of leaves or blossoms like a chickadee searching for small insects, beetles, flies, moths, larvae, and egg clusters. Some flying insects are taken on the wing; and occasionally the bird may be seen feeding on the ground.
Dr. Wetmore (1916) reports on the contents of 61 stomachs from Porto Rico, which contained 97.7 percent animal matter and only 2.3 percent vegetable matter. The latter “consisted of seeds of small berries of the camacey (Miconia prasina) and others.” In the animal food, beneficial insects and a large number of spiders amounted to about 35 percent, and the remainder were all harmful pests. “Lantern flies (Fulgoridae) (19.09 percent) were identified in 29 stomachs. * * * Other bugs (3.69 percent) comprise small numbers of leaf bugs, species of the chinch bug family, stink-bugs, and a few predaceous assassin bugs. The birds are fond of beetles, and this order supplies 22.53 percent of the food, nearly all being injurious species. Ladybird beetles (1.36 percent) were present in 14 stomachs. Longicorn beetles (1.68 percent) were taken 11 times, and leaf beetles of several species (7.95 percent) were eaten by 30 of these birds.” Other beetles taken included darkling beetles, skin beetles, scarred-snout weevils, coffee leaf-weevils, stalk borers, and curculios. Among other items were a few ants and other small Hymenoptera (3.57 percent) and flies (1.19 percent). Caterpillars were found in 18 stomachs and moths in 4. Spiders (29.53 percent) were identified in 29 stomachs. Stuart T. Danforth (1925), from Puerto Rico, adds berries of Varronia angustifolia and fleabeetles, and says that large moth eggs were eaten by two birds, forming 25 percent of their food. Forbush (1929) says that “it feeds much on small hairless inch-worms, such as the fall canker-worm and the spring canker-worm, and on the younger and smaller hairy caterpillars, such as the gipsy and the tent caterpillar.”
Behavior.—The parula warbler is less active in its movements, more sedate and deliberate, than most of the other tree-top wood warblers.
It creeps along the branches and hops from twig to twig, often clinging to the under side of a cluster like a chickadee, an action that led some of the early writers to refer to it as a small titmouse, and it sometimes clings to the trunk of a tree like a nuthatch in its search for food. The birds are fearless and confiding, and are easily approached. Even when their nest is disturbed they come within a few feet of the intruder, making little, if any, protest or demonstration. George B. Sennett (1878) tells the following story, illustrating the confiding nature of the bird:
Just before we sighted land, imagine our surprise and joy to see a little Blue Yellow-backed Warbler on our mast. It soon flew down to the sail and thence to the deck, where, after a few moments, it felt quite at home. Our sailor caught him, and he was passed around for all to admire and pet. It would nestle in our hands and enjoy the warmth without the least fear. When allowed his freedom, he would hop upon us, fly from one to another, and dart off over the side of the boat as if taking his departure; when lo! back he would come with a fly or moth he had seen over the water and had captured. Several flies were caught in this way. He searched over the whole boat and into the hold for insects. Often he would fly to one or the other of us, as we were lying on the deck, and into our hands and faces, with the utmost familiarity. He received our undivided attention, but could have been no happier than we. Upon reaching shore, amid the confusion of landing we lost sight forever of our pretty friend.
Voice.—The parula warbler has a simple, but to my ears a very distinctive, song. In 1900 I recorded the song in my notes as “pree-e-e-e-e-e-e, yip, a somewhat prolonged trill like a pine warbler’s, but fainter and more insect-like, ending abruptly in the short yip with a decided emphasis.” I have always been able to recognize it by the explosive ending, which I never heard from any other wood warbler.
Gerald Thayer wrote to Dr. Chapman (1907) as follows:
The Parula is weak-voiced, and its call notes, as far as I know, are slight and barely peculiar; but it has at least three main songs, with great range of variations.
All may be recognized, or at least distinguished from the weak songs of the Dendroicae, like the Blackburnian and Bay-breast, by their beady, buzzy tones. In phrasing, in everything but tone-quality, certain variations of the Parula’s and of the Blackburnian’s songs very nearly meet and overlap; but the tell-tale tones remain unchanged,—wheezy and beady in the one, smooth as glass in the other. Commonest of the Northern Parula’s three main songs is probably the short, unbroken buzz, uttered on an evenly-ascending scale, and ending abruptly, with a slight accentuation of the final note. Next is that which begins with several notes of the same beady character, but clearly separated, and finishes, likewise on an ascending scale, with a brief congested buzz. The third main song is based on an inversion of the second—a buzz followed by a few separate drawled notes, high-pitched like the buzz-ending of the two other songs. All these vary and intervary perplexingly.
Aretas A. Saunders contributes the following notes on the song of this warbler: “The parula warbler has two distinct types of song. One is a simple buzzy trill rising in pitch, and frequently terminated by a short, sharp note of lower pitch. Of 12 records of this song, 7 have the terminal note and 5 do not. The other form has the same buzz-like quality, but begins with three or four short notes on the same pitch, followed by a longer, higher note that is frequently, but not always, slurred upward. Both songs are similar in length and in pitch intervals. They vary from 11⁄5 to 13⁄5 seconds in length. The rise in pitch varies from one to four and a half tones, and averages about two tones. The actual pitch is exceedingly variable in individuals and varies from A‴ to D‴″. Songs vary considerably in loudness, many of them becoming suddenly louder toward the end.