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Eastern Bluebird

Sialia sialis

Order:
Passeriformes
Family:
Turdidae
Sections

Diet and Foraging

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Figure 2. Foraging methods of Eastern Bluebirds in Clemson, SC, 1996.

Samples based on focal individual samples during egg-laying stage of nest cycles throughout breeding season.

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Adult female Eastern Bluebird (Sialia sialis) feeding on Winterberry (Ilex sp.) fruits in winter, Ithaca, New York, January.

Fruit is key to the diet of this species in winter., Jan 01, 2000; photographer M. Read

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Adult female Eastern Bluebird, feeding young; Ohio, July.

Washington Co. Ohio; plumage of adult is Alternate (worn), that of young is Juvenal., Jul 15, 2004; photographer J. ZICKEFOOSE

Feeding

Main Foods Taken

Insects, spiders, small fruits (Forbes 1903, Beal 1915b, Pinkowski 1977c), and the occasional small vertebrate, including salamanders (PAG) and small snakes (Braman and Pogue 2005).

Microhabitat For Foraging

Generally a sit-and-wait predator; individuals use available perches for staging foraging attempts at ground-living arthropods. Staging sites are usually 0.5 - 15 m above bare ground, grassy areas, and in forest areas with sparse understories. When searching for ripe fruit, individuals land on stalks of fruiting bushes or in fruiting clumps in trees (PAG, JHP).

Foraging Areas

See Habitat, above. Often in open habitats, with little or no overstory and sparse ground cover, such as old fields, pastures, and orchards. During the nonbreeding season, bluebirds forage in forested areas with more or less closed canopy, sparse ground cover, and shrubby edges (PAG, JHP).

Food Capture And Consumption

Hunt for prey from lookouts while perched upright; locate ground arthropods visually, sallying to the ground to capture prey. Individuals identify appropriate prey from distances of 15–20 m, sometimes as far away as 40 m, suggesting eyesight is comparable to that of flycatchers (Preston and McCormick 1948). Drop-foraging constitutes the method of almost 100% of foraging attempts during the early breeding season in Michigan (Pinkowski 1977c) and in S. Carolina and Georgia (PAG); fly-catching, gleaning, and hopping increase in frequency during the summer, fall, and winter, although dropping from a perch is the most frequent foraging method in all seasons (Figure 2). During the breeding season, 80% of foraging attempts are perch-to-ground movements. Hovering is uncommon. There are no significant differences between the sexes in foraging mode.

Take ground arthropods in their beaks; often consume prey at the point of capture, though may take large prey items to a perch and bang the prey item against a substrate by moving their heads from side to side, then consuming the prey. Younger fledglings hop along the ground to forage before acquiring adult drop-foraging habits. Foraging during the breeding season peaks in the morning hours in S. Carolina and Georgia, is lowest at midday, and increases toward evening (PAG unpubl. data). No comparable, systematic data exist on winter foraging habits.

Diet

Major Food Items

During the breeding season, ground arthropods. In late summer and into winter, add small fleshy fruits to their mostly insect diet.

Quantitative Analysis

In Michigan, from samples over an entire year, the major food items of adults included butterfly and moth larvae (Lepidoptera; 32.4%), grasshoppers and crickets (Orthoptera; 25.6%), spiders (Araneida; 11.3%), and beetles (Coleoptera; 30.7%); also mistletoe (Phoradendron californicum) and sumac (staghorn sumac [Rhus typhina] berries, as well as those of smooth sumac [R. glabra]; Pinkowski 1977c). In Illinois, the stomach contents of 108 individuals sampled throughout a year included 78% insects; 8% spiders; 1% other invertebrates; and 13% fruits (Forbes 1903).

Stomach contents of 855 individuals taken in every month from 28 states and parts of Canada included 68% invertebrate prey and 32% wild fruits (Beal 1915b). In stomach analyses, insect prey predominated during the breeding season, and wild fruits during the nonbreeding season. Eastern Bluebirds frequently eat crickets and grasshoppers, which were in half the stomachs sampled. Beetles, butterflies, and moths equaled 20% each of the total sample. Fruits of 60 species were in stomachs of individuals collected in late fall and winter, Oct–Feb. Three-fourths of all the fruit in bluebirds' stomachs were from individuals collected in winter. Seeds represented < 0.6% of contents. Occasionally reported foods included shrews (Microsorex sp. or Sorex sp.; Pinkowski 1974e); snakes (Flanigan 1971); salamanders (on video shot by D. Droge and PAG); lizards; and tree frogs (Bent 1949).

In Ohio, bluebirds took large items more often and small items less often than statistically expected, based on the frequencies of available large and small prey; prey items greater than the length of a bluebird's bill equaled only 21% of available prey items, but represented 56% of items that bluebirds ate (Goldman 1975). Detailed studies from most parts of the range of bluebirds are not available. See Breeding: parental care, below, for list of foods fed to nestlings.

Food Selection and Storage

In Athens, GA, experiments (Davison 1962) showed that under conditions controlling for their seasonal availability, bluebirds take a variety of fleshy winter fruits. The fruits bluebirds took included: blackgum (Nyssa sylvatica), blueberry (Vaccinium sp.), camphortree (Cinnamomum camphora), black cherry (Prunus serotina), dried current (Ribes sp.), dahoon (Ilex cassine), flowering dogwood (Cornus florida), autumn elaeagnus (Elaeagnus umbellata), cherry elaeagnus (E. multiflora), thorny elaeagnus (E. pungens), sugar hackberry (Celtis laevigata), American holly (Ilex opaca), amur honeysuckle (Lonicera maachi), Japanese honeysuckle (L. japonica), laurelcherry (Prunus laurocerasus), redbay persea (Persea borbonia), common pokeberry, (Phytolacca mericana), pyracantha (Pyracantha sp.), nectar raisins (Vitis sp.), redcedar (Juniperus virginiana), Carolina snailseed (Cocculus carolinus), smooth sumac (Rhus glabra). No observers report bluebirds storing food.

Nutrition and Energetics

Nutritional requirements remain unstudied. Also very few systematic, controlled studies of energetics. Of the 3 bluebird species, Eastern Bluebirds have the highest wing-loading: 0.298 g/cm2 (Pinkowski Pinkowski 1977c, Pinkowski 1978a), consistent with the fact that individuals use less airborne foraging than Western and Mountain bluebirds do.

From Buser 1980: average energy expenditure, based on time budget estimates during the breeding season, for 6 pairs with 4 nestlings evaluated in each year, was 70 kJ/d for males and 74 kJ/d for females. The overall similarity obscures the differences in distribution of female and male energy expenditures. For aspects of parental care that have to do with direct care of nestlings (excluding nest construction and incubation, which are activities of females alone), females expend more than twice as much energy as males. In New Jersey during the nest-building phase, females expend about 2.61 kJ/h building nests, about 1.38 kJ/h incubating; in the nestling phase, they expend about 0.97 kJ/h brooding nestlings in first week of life and about 0.16 kJ/h brooding in second week. Females spend about 0.58 kJ/h providing food to nestlings during first week and 1.34 kJ/h during the second week. In contrast, males expend about 0.68 kJ/h providing food to nestlings in first week of nestling life and about 0.65 kJ/h in second week. During week 1 of nestling life, females spend an average of 47.3% of their time in nestling care (n = 6); while males spend 18.2% (n = 6). During the nestling phase, males spend an average of 56.7% of their time foraging and 15.3% of their time off territories (n = 6); females spend 40.2% of their time foraging and 4.7% of their time off territories (n = 6; Buser 1980).

Metabolism and Temperature Regulation

No systematic, controlled studies of general metabolism or of temperature regulation in adults. Nestlings have endogenous thermoregulatory abilities by around 5–7 d of age (see Breeding: young birds, below). Communal roosting during winter in holes in trees and other cavities of 2 to several dozen individuals during particularly cold nights is a habit that conserves warmth (Frazier and Nolan 1959, Pitts 1977b). During especially cold days, bluebirds retreat to heating sources such as chimney tops of gas-burning stoves (Parker and Parker 1950). Metabolic rates of nestlings aged 12–14 d in the field were measured by the use of the doubly-labeled water technique; indicated no significant differences between males and females in CO2 production (Droge et al. 1991).

Drinking, Pellet-Casting and Defecation

Drink from ponds, streams, and birdbaths. Casual observations indicate that captives seem to prefer running water to standing water. Adults defecate in flight and while perched.

Recommended Citation

Gowaty, P. A. and J. H. Plissner. 2015. Eastern Bluebird (Sialia sialis), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.381