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American Redstart

Setophaga ruticilla

Order:
Passeriformes
Family:
Parulidae
Sections

Diet and Foraging

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Feeding

Main Foods Taken

In the breeding season, American Redstarts feed mostly on insects, including leafhoppers and planthoppers (Homoptera), flies (Diptera), small and mostly parasitic wasps (Hymenoptera), beetles (Coleoptera), and moths and their caterpillar larvae (Lepidoptera; Bent 1953b, Robinson and Holmes 1982; K. Judson and TWS, unpublished data). Some small berries and fruits in late summer (Bent 1953b). During overwintering period, also insectivorous, feeding mainly on small flies, leafhoppers and planthoppers, bark lice (Psocoptera), beetles, small wasps and ants, and beetles (Sherry 1985; K. Judson and TWS, unpublished data; RTH).

Microhabitats for Foraging

Breeding Period. Forages from ground to near top of canopy (Williamson 1971, Robinson and Holmes 1984, TWS). In northern hardwood forest at Hubbard Brook Experimental Forest, New Hampshire, males and females foraged at similar heights (10.9 m ± 0.8 SD [n = 1,111] and 11.3 m ± 4.6 SD [n = 510], respectively), obtaining 64–75% of prey from foliage, 23–31% from air, 1–4% from twigs and branches, and < 1% from ground (Holmes 1986). In New Brunswick, however, female tends to forage lower than male, often near (but not on) ground (R. E. Lemon, personal communication), possibly because females nest lower there than at Hubbard Brook (see Breeding: Nest Site). Forages in all parts of trees, but tends to take prey from twigs, branches, and leaves (Williamson 1971, Robinson and Holmes 1984, Holmes 1986, TWS). Sometimes concentrates temporarily on taking adult moths and other prey from tree trunks, presumably when such prey are relatively abundant on such substrates (TWS). Differs from most other wood-warblers by taking more flying prey, but overlaps and competes with other fly-catching species, such as Least Flycatcher, for same kinds of insect prey (Holmes et al. 1979b, Sherry 1979, Sherry and Holmes 1988).

In New Hampshire, captured arthropod prey about equally from upper and lower leaf surfaces (42% and 47%, respectively), in contrast to several species of Setophaga (previously Dendroica) warblers, which take prey mainly from lower leaf surfaces (Holmes and Schultz 1988). However, this depends on tree architecture when controlling for prey type (Whelan 2001): For example, in experiments with mealworm pieces as prey, redstarts predominantly captured prey from lower surface of typically raised leaves (above the branch = perch) of sugar maple (Acer saccharum) but from upper surface of planar yellow birch (Betula alleghaniensis) leaves at the bird’s foot, in both cases using energetically most economical foraging tactics (gleans rather than hovers). When individuals attack less accessible lower surfaces of yellow birch, they tend to use aerial hover tactics, much as when attacking prey on upper surfaces of sugar maple. Aerial attacks are also used more frequently to attack prey on lower leaf surfaces, and prey at greater distances from the bird. Different species of Setophaga, despite overall similarities in leg and wing morphology, attack prey differently compared to redstarts, and to other species when confronted with different foliage structure (Whelan 2001).

While in molt, tends to forage using relatively economical behaviors (hops, gleans, infrequent sallies, and few aerobatic pursuits of prey or long flights), and tends to stay in relatively dense vegetation, sometimes high in canopy, and to give infrequent (soft) songs (TWS), perhaps because reduced wing and tail surface area from temporarily lost remiges and rectrices either decreases efficiency of aerial foraging attacks and/or increases vulnerability to predators.

Overwintering Period. Similar to breeding season. Forages over full vertical range of woodland or forest habitats (RTH, TWS), but concentrates at middle heights in vegetation (e.g., 6–12 m in rain forest and tall mangroves, 36 m in secondary scrub woodland; Bennett 1980). Prey taken most frequently from air (40–70%), or foliage (28–50%), but also occasionally from tree trunks (Jeffrey-Smith 1972) or ground (Lack and Lack 1972, Bennett 1980, Lovette and Holmes 1995), particularly in open habitats such as in pneumatophores of mangrove trees (TWS; P. P. Marra, personal communication). Females shift from near-perch (glean, reach, and hang) to more energetically expensive aerial tactics (hawk, hover, hover-glean) over the overwintering period in poorer (drought-prone, deciduous) thorn scrub habitat, but not adjacent black mangrove habitat in Jamaica, either because of changes in the availability of prey types or increasing leaf drop allowing better detection of flying and more distant prey (Powell et al. 2015). These foraging behaviors are also related to body condition (see Demography and Populations: Population Limiting Factors).

Food Capture And Consumption

Forages alone, although members of pair sometimes forage near one another and occasionally join mixed-species flocks in nonbreeding season (Morse 1970b, Ewert and Askins 1991, Latta and Wunderle 1996b, TWS).

Breeding Period. Both male and female move rapidly while foraging (Williamson 1971, Robinson and Holmes 1982, Lovette and Holmes 1995). Spreads and displays (“flashes”) wings and tail, presumably to flush prey (Root 1967), particularly while provisioning nestlings and fledglings, but also frequently during the overwintering period (Lovette and Holmes 1995, TWS). In yellow birch, compared with other tree species in northern hardwood forest, responds with increased attack rate, and with increased frequencies of flush-chase tactics (i.e., prey is startled into flight and pursued) and tail fanning, presumably to help flush relatively abundant leafhoppers (Cicadellidae) found in yellow-birch foliage (Robinson and Holmes 1984). Searches different northern hardwood-tree species approximately in proportion to availability (Holmes and Robinson 1981). When actively foraging, hops and flies rapidly between perches, changing perch 27–30 times/min on average (Williamson 1971, Robinson and Holmes 1982). Gleans prey, makes short hovering maneuvers to attack prey on leaves, often tumbles aerobatically while chasing prey flushed from foliage, and makes mostly short sallies (up to about 5 m) into air to catch flying prey (Ficken 1962b, Robinson and Holmes 1982, TWS). Unlike some tyrannid flycatchers, rarely returns to same perch from which it initiates aerial attack (TWS). Its mean search radius (distance over which it perceives and attacks prey) is 53 cm ± 5.3 SD (n = 522) with little variation among tree species; attacks prey at average rate of 5.0–5.6/min (Robinson and Holmes 1982, Robinson and Holmes 1984, Lovette and Holmes 1995). Whacks large prey items forcefully against perch to subdue prey, in the case of caterpillars to remove gut contents, and to remove wings of large moths (Ficken 1962b, TWS). An adult that is provisioning nestlings feeds much of the day, uses energetically demanding tactics, and captures prey at a high rate, suggesting that food demand is high relative to availability (Lovette and Holmes 1995). Female may find incubation particularly demanding in northern breeding latitudes, on basis of relatively high rate of foraging (Sherry 1975) and on the very small prey items taken every few seconds then (TWS), presumably because females have little time to forage while maintaining constantly high egg temperature for rapid embryo development in a cool temperate climate.

Overwintering Period. Foraging tactics and movements similar to those in summer, but aerial sallies and flush-chases are proportionately more common (Bennett 1980, Sherry 1985, Lovette and Holmes 1995). On average, rate of movement while foraging is faster in winter than in summer, proportion of time spent foraging is greater, and rate of attacks on prey is lower (2.4–2.8/min), observations consistent with food being less abundant or less accessible in winter than in summer (Lovette and Holmes 1995). Can catch up to 8–13 insects/min during overwintering period (Jeffrey-Smith 1972).

In general, foraging behavior is flexible, depending on individual and time of day (Holmes et al. 1978a, Ficken 1962b), season (Lovette and Holmes 1995, TWS), habitat (Maurer and Whitmore 1981, Woodrey 1995, Powell et al. 2015), tree species and strata within a forest (Robinson and Holmes 1984), and tree architecture (Whelan 2001). Opportunistic response of redstart to unusual opportunities is reinforced by anecdotes: holding a territory around a garbage container in Mexico (S. Bennett, personal communication) and around latrines and chicken coops in Jamaica (source of a common name “latrine bird” there; K. Levy and L. Douglas, personal communication); and feeding at night on insects attracted to a window (Bakken and Bakken 1977). Individuals also forage actively in rainforest interior of Cocos Island, Costa Rica, a habitat rarely used by other migrant warblers, and facilitated by ability to flush and chase the proportionately abundant planthoppers (Hemiptera, Fulgoroidea) there (Sherry 1985). Diet opportunism supported (Sherry et al. 2016) based on diets in shaded coffee plantations in Jamaica: guts contained similarly small, available insect prey to four other overwintering migrant warblers, and prey were small (many < 2 mm length) and often patchily distributed among the gut samples within a foraging species, indicative of foraging regularly on small patches of aggregated prey. Thus, redstarts are evolutionarily generalized—i.e., behaviorally opportunistic—in terms of foraging behavior. This opportunism is consistent with the seasonally changing demands and diverse ecological conditions encountered annually (Sherry 1990).

Convergent in terms of morphology and associated foraging behavior not only with Myioborus warblers, but also with New World and Old World flycatchers (Holmes et al. 1979b, Sherry 1979, Bennett 1980, Keast et al. 1995). Has flattened flycatcher-like beak—depth 66% of width (Keast et al. 1995; see also Table 1), proportionately large wing area (i.e., low wing-loading) and large tail area for aerobatic attacks and pursuits of evasive insect prey, and rictal bristles typical of tyrannid flycatchers that pursue prey aerially (Bennett 1980, Sherry 1983, Keast et al. 1995). Distinctive wing and tail flash patterns (contrasting colors exposed by fanning wings and tail during foraging) make this species unique among North American passerines (Keast et al. 1995). Morphological, foraging behavioral, and dietary similarities of American Redstart to Least Flycatcher appear to underlie their competitive ecological interactions on breeding grounds (Sherry 1979, Sherry and Holmes 1988, Martin et al. 1996a, TWS).

Diet

Major Food Items

American Redstart shows considerable foraging and dietary flexibility not just in relation to the factors mentioned above, but also in relation to local prey types available (K. Judson and TWS, unpublished data). Flies, moths, and leafhoppers and planthoppers are almost always well represented in diet, probably because of redstart’s unique morphological adaptations for aerial flycatching and pursuit. Depending on weather in spring, frequently hawks midges (Diptera: Chironomidae) in conifer treetops, which provide readily available food when individuals first arrive at breeding areas with nearby wetlands (Smith et al. 2007e); will feed at ground level on snow surface, eating insects immobilized by cold temperatures (R. E. Lemon, personal communication). In summer, feeds extensively on flies, leafhoppers and planthoppers (and occasionally aphids), caterpillars (mostly of moths), adult moths, small wasps, beetles, stoneflies (Plecoptera) in New Hampshire due to abundant small streams, spiders (Araneae: Araneida), and other small invertebrates found in foliage (Robinson and Holmes 1982; Diets of breeding individuals in Louisiana overall very similar to New Hamphsire (K. Judson and TWS, personal communication). Occasional summer and fall use of small berries and fruits, including serviceberry (Amelanchier), Magnolia, and barberry (Berberis) (Bent 1953b, Griscom and Sprunt 1957, Imhof 1976). During overwintering periods, largely insectivorous (Wetmore 1916a, Lefebvre et al. 1992, Sherry et al. 2016; K. Judson and TWS, unpublished data). Fewer caterpillars and smaller prey eaten in winter than in summer (K. Judson and TWS, unpublished data). Beetles, moths, wasps, planthoppers, flies, and spiders reported from the stomachs of 13 redstarts collected in Puerto Rico (Wetmore 1916a in Bent 1953b). In black mangrove habitat in Panama, consumes primarily small Homoptera and small insect eggs (76% of diet), based on a few regurgitation samples from sites on both Pacific and Caribbean coasts (Lefebvre and Poulin 1996).

Quantitative Analysis

Breeding Period. On basis of 176 identifiable prey in emetic samples from 44 American Redstarts captured in northern hardwood forest at Hubbard Brook, New Hampshire: leafhoppers and planthoppers 35%, flies 30%, beetles 13%, wasps 12%, moths and caterpillars 6%, spiders 1%, and other 3% (Robinson and Holmes 1982). Field observations of 55 prey taken by redstarts in this same study indicate the following: caterpillars 67%, moths 26%, other 7% (Robinson and Holmes 1982). A total of 893 identifiable arthropod prey identified in 41 gut samples from Hubbard Brook, May–July (K. Judson and TWS, unpublished data) included 35.3% flies, 34.5 Hemiptera (including former Homoptera), 9.7% caterpillars and moths (in about equal proportions), 6.3% ants and parasitic wasps (including some larval and adult sawflies; Hymenoptera), 6.3% beetles, 4.1% spiders, 2.6% stoneflies; and < 1% each of mayflies (Ephemeroptera), bark lice, lacewings (Neuroptera), caddisflies (Trichoptera), and scorpionflies (Mecoptera).

Overwintering Period. In Venezuela mangroves, diet dominated by beetles (37%), leafhoppers and planthoppers (30%) and flies (9%); stomach contents also included some insect larvae, grasshoppers (Orthoptera), spiders, true bugs (Hemiptera), and caterpillars, each making up < 6% of total (Lefebvre et al. 1992). In Jamaica, the most important prey items in black mangrove habitat: Hymenoptera (especially parasitic wasps) 29%, flies 26.2%, beetles 15.4%, leafhoppers and planthoppers 9.4%, bugs 9.4%, and spiders 6% (149 items, n = 7 stomach samples); in a Jamaican dry forest: wasps 43%, leafhoppers and planthoppers 28%, and beetles 23% (102 items, n = 5 stomach samples; TWS). Stomach of a female foraging on Cocos Island, Costa Rica, contained 91% planthoppers, the prevalent prey available there in understory where bird fed (11 items; Sherry 1985). Gut samples from two shaded coffee plantations in Jamaica contained 37.8% psyllid Hemiptera and 2.5% other Hemiptera, 18.3% coffee berry borer beetles (Coleoptera: Scolytidae) and 7% other beetles, 13.9% bark lice, 3.9% ants and 8.0% other small wasps, 2.8% midges and 3.5% other flies, 1% thrips (Thysanoptera), and < 1% each of spiders, lacewings, caterpillars and adult moths (1,353 identifiable prey items, n = 22 emetic samples; Sherry et al. 2016). This same study showed extensive diet overlap with four other overwintering warbler species, but a significant tendency for redstarts compared to the other species to consume more flies and small wasps, probably in relation to redstart’s relatively aerobatic foraging capacity (see above).

Migratory Period. Diets of individuals collected during Spring migration (April–May) or Fall migration/winter (September–December) in coastal Louisiana and Texas (698 identifiable prey items, n = 22 stomach samples) consisted of 40.1% flies (including 13.5% midges), 17.2% leafhoppers and planthoppers, 11.6% small wasps and ants, 10.6% beetles, 8.9% bark lice, 2.9% spiders, 2.7% caterpillars and moths, 1.4% mayflies, 1.3% lacewings, and < 1% each of Odonata, Orthoptera, and mites (Acari) (K. Judson and TWS, unpublished data; Louisiana State University Museum of Natural Science specimen data). Stomach of migratory bird in California contained 5 leafhoppers, 4 beetles, and 1 moth (Root 1962). Aquatic insects such as midges can be important food during migration (K. Judson and TWS, unpublished data), even causing redstarts to alter their foraging behavior (Smith et al. 2004c).

Food Selection and Storage

Not known to store food.

Nutrition and Energetics

No studies expressly on nutrition or energetics available. For latter, however, fast-moving foraging style of this species should result in relatively high daily energy expenditures. Bennett 1980 and Lovette and Holmes 1995 present analyses of foraging behavior suggesting that individuals have to work harder during the overwintering period than in summer to get enough food.

Metabolism and Temperature Regulation

No information.

Drinking, Pellet-Casting and Defecation

No information.

Recommended Citation

Sherry, Thomas W., Richard T. Holmes, Peter Pyle and Michael A. Patten. 2016. American Redstart (Setophaga ruticilla), version 3.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/bna.amered.03