Main Foods Taken
Breeding period. Insectivorous, feeding extensively on Lepidoptera larvae and adults, crane flies (Tipulidae: Diptera) and other adult Diptera, spiders and other arthropods, and small snails (Robinson and Holmes 1982, Rodenhouse and Holmes 1992, RTH).
Overwintering period. Some Lepidoptera larvae, leaf hoppers, beetles, flies, and small berries and fruits (Wetmore 1916a, RTH); also feeds at flowers, possibly for nectar and/or insects (RTH; J. M. Wunderle, personal communication). In Dominican Republic, feeds frequently on honeydew excretions from scale insects (Latta et al. 2001).
Microhabitats for Foraging
Breeding period. Forage from the ground to high in the canopy, but mainly in the lower to mid strata, with males foraging on average higher than females (5.9 m ± 3.8 SD and 3.3 m ± 3.0 SD, respectively; Holmes et al. 1986). Foraging is more concentrated at shrub and lower canopy strata than other coexisting species, which may contribute to ecological segregation (Holmes et al. 1979b). Based on studies in New Hampshire, 71–79% of arthropod prey are obtained from foliage, 4–13% from branches and twigs, 6–8% from the air, and < 1% from the ground (Holmes et al. 1979b, see also Holmes and Schultz 1988). Prey are taken primarily from the undersurfaces of leaves, with 82% of all foraging maneuvers directed toward foliage (Holmes and Schultz 1988; see Figure 3). In laboratory experiments, learned to locate and capture prey more proficiently from lower leaf surfaces than did Black-throated Green Warblers (Setophaga virens; Whelan 1989a, Whelan 2001). However, individuals shift readily among prey types and surfaces examined, taking advantage of changes in prey availability (RTH).
Overwintering period. Few quantitative data, but food searching behavior appears similar to that in the breeding season (RTH). In Jamaica, foraging height averaged 4.5 m ± 4.0 SD (n = 152), and most foraging attacks were directed towards prey on broad-leaved foliage (46%), with the remainder on twigs (13%), air (17%), ground (15%), and fruit and flowers (8%; n = 350, Lack and Lack 1972). A single male in Ecuador attacked prey from live foliage of trees (68%), and epiphytes (11%), live leaf petioles (13%), and in the air (8%), (n = 38 observations, Martin et al. 2004d). In shade-coffee plantations, forage more frequently among the foliage of overstory trees (mostly Inga) than among the coffee bushes (Wunderle and Latta 1998, Jirinec et al. 2011).
Food Capture and Consumption
Forage alone, although members of a pair sometimes forage near one another.
Breeding period. Males spend 30–32% of daylight hours foraging, plus another 19–20% when they both forage and sing (Black 1975). Females forage 50–70% of the time during nest building and egg laying, declining to only 22% during incubation, but then increasing to 70–80% during feeding of nestlings (Black 1975). Males forage at higher rates when feeding nestlings and fledglings than during the incubation period, although the rates at which they attack prey do not differ between the time periods (Dobbs et al. 2007). Foraging behavior also varies with population density. Males with experimentally reduced neighbor density spent proportionally more time foraging than control males when their social mates were building nests, laying eggs, and incubating (Sillett et al. 2004); males with experimentally reduced neighbor density also reduced their use of aerial attack maneuvers compared to control males (Dobbs et al. 2007).
When foraging, both sexes visually search upper and especially lower leaf surfaces, branches and twigs, tree boles, and surrounding air spaces by moving rapidly through dense foliage (Robinson and Holmes 1982, Robinson and Holmes 1984, Holmes et al. 1986). At these times, they change perches at an average rate of 26 times/min, hopping slightly more often than flying (Robinson and Holmes 1982). Their search radius (the distance over which they attack potential prey) averages 53.0 cm ± 4.0 SD (n = 558), and they attack prey at a rate of 2.2/min ± 0.2 SE (n = 142 foraging sequences; Robinson and Holmes 1982). The most frequent prey capture method is to snatch prey from a substrate, usually a leaf, while hovering or flying past (65%); secondly (35%), they glean prey from nearby substrates while standing on the vegetation (Robinson and Holmes 1984). Unlike other species in northern hardwood forests, they do not change their relative use of foraging maneuvers or search tactics among tree species or strata, suggesting more stereotyped foraging behavior (Robinson and Holmes 1984). In laboratory experiments, their foraging behavior changes with leaf shape and position in relation to available perches (Whelan 1989b, Whelan 2001), suggesting that plant morphology influences their foraging success. Capture methods and substrates searched shift rapidly with changes in food availability, and individuals may focus on one abundant prey type during the period that it is available (NLR).
Overwintering period. Few quantitative data available. From studies in Jamaica (Lack and Lack 1972), 72% of foraging maneuvers were made by perched birds (presumably gleans), 18% in the air, 8% by hovering, and 2% by fluttering from a perch (n = 350). If these data are representative, these birds apparently switch from primarily gleaning insectivorous prey from leaf undersurfaces in summer to capturing prey from foliage during the overwintering period. Also, obtain nectar from flowers and pluck berries and small fruits from understory shrubs (Wetmore 1916a, Wunderle 1995, Martin et al. 2004d, RTH). In shade coffee plantations in the Dominican Republic, foraged mostly in the overstory tree canopy (mostly Inga), where it mostly gleaned prey from leaves, but also hovered and probed a variety of substrates, including flowers, bark, and lichens (Wunderle and Latta 1998). When foraging among the foliage of coffee, only 14% of foraging maneuvers were directed towards prey on leaves (Wunderle and Latta 1998). Studies in Jamaican coffee plantations show that foraging by this species, in conjunction with that of other co-occurring, mostly overwintering Neotropical migrants, significantly reduce the numbers of foliage-eating insects, particularly the coffee berry borer, Hypothenemus hampei (Kellermann et al. 2008; see also Sherry et al. 2016).