Food Habits

Main Foods Taken

In breeding season, adults: principally arthropods, including primarily insects, but occasionally spiders and also small mollusks (Linsdale 1928a). Also occasionally seeds, fruit, and plant matter (Linsdale 1928a, Grinnell et al. 1930, Austin 1932, LSUMNS, University of Washington Burke Museum [UWBM]). Outside the breeding season, adults more omnivorous—a mixture of fruits, seeds, insects, and occasionally buds of plants (Judd 1901, Linsdale 1928a, Grinnell et al. 1930, Schmid 1958, LSUMNS, UWBM). For nestlings: see Breeding: parental care, below.

Microhabitat For Foraging

Nests and feeds in same microhabitat (see Breeding: nest site, below). Generally feeds in leaf litter; may pick insect food items off growing vegetation (Grinnell et al. 1930). In winter and during migration, feeds in leaf litter under fairly thick cover (Austin 1968, Terrill 1968), either on borders of woods, second growth, or even among scattered brush cut from recently felled trees (Linsdale 1928a). During prolonged snowfall or freezing rain, may leave shelter of thickets and thick cover to forage in the open (Terrill 1968). During Mar at Patuxent Research Refuge in Maryland, 5–10 Fox Sparrows fed daily under a large willow oak (Quercus phellos), and many others were seen feeding under multiflora rose (Rosa multiflora) hedges (Schmid 1958).

Food Capture And Consumption

Forages in leaf litter and on bare ground using a “double-scratch” movement—both feet moved synchronously to disturb the ground and leaf litter (Hailman 1973, 1976). Apparently sees insects best when 15–30 cm away (Grinnell et al. 1930). May fly from perch to air to capture flying insects (Linsdale 1920, R. Zink pers. comm.).

Major Food Items

During breeding season: beetles and weevils (Coleoptera), fly larvae (Diptera), caterpillars (Lepidoptera), ants and bees (Hymenoptera), scale insects (Homoptera), spiders (Arachnida), millipedes (Diplopoda), small mollusks (Bivalvia and Gastropoda), and seeds and fruits of Carex sp., Rubus sp., Potentilla sp., Diodia sp., and serviceberry (Amelanchier sp.; Linsdale 1928a, Grinnell et al. 1930). Known to feed on dead and dessicating fish along beaches (Terrill 1968). On wintering grounds: fruits of American strawberry bush (Euonymus americana), red cedar (Juniperus virginiana), pokeweed (Phytolacca americana), blueberries (Vaccinium sp.), elderberries (Sambucus sp.), blackberries (Rubus sp.), grapes (Vitis sp.), witch hazel (Hamamelis sp.) buds, and seeds of ragweed (Ambrosia sp.), smart weed (Polygonum sp.), hounds tongue (Cynoglossum sp.), Lythospermum sp., Panicum sp., sorrel (Rumex sp.), Phleum pratense, and other “weeds” (Judd 1901, Linsdale 1928a, Terrill 1968). In spring and during migration, feed on arthropods and seeds (see Feeding, above) and withered, fallen fruits from previous year (Austin 1968). Individuals collected in Mar, Apr, and May had fruit seeds in their stomachs, including seeds of blueberries, elderberries, blackberries, grapes, and multiflora rose (Schmid 1958, Austin 1968). Stomachs commonly contain grit, gravel, or soil detritus (Linsdale 1928a, LSUMNS, UWBM, Bell Museum of Natural History [MMNH]).

Quantitative Analysis

Recent data lacking. Analysis of stomachs from 10 individuals from Esmeralda Co., NV, however, indicates that Hymentopera made up 71% of food items taken by Fox Sparrows during May, Coleoptera 16% (Linsdale 1928a). Stomachs of 2 P. i. iliaca collected in Apr were almost completely filled with seeds plus parts of 2 ground beetles (Carabidae; Linsdale 1928a). Ground beetles and millipedes made up about 30% of food taken by migrant Fox Sparrows collected in the e. U.S. (Judd 1901, Terrill 1968). Stomachs of 127 Fox Sparrows collected Sep–Apr in e. U.S. contained 86% plant matter and 14% animal matter; seeds of berries and fruit skins made up 28% of food taken during winter; millipedes 20% of all food items taken during migration (Apr; Judd 1901). Of 36 specimens collected throughout the year, 80.5% of stomachs held seeds; 25% insect parts; 5.6% berries; 11.1% plant matter; and 8.3% grit, soil, or other detritus (LSUMNS, UWBM, MMNH).

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From Rogers and Rogers 1990 . Evening and dawn body mass and fat class vary seasonally and in parallel (p < 0.0001, for all 4 comparisons). Fox Sparrow exhibits a seasonal increase in dawn body mass and visible fat class as midwinter approaches, and then a decrease in dawn body mass and visible fat class toward spring. Individuals overcompensate for nightly mass loss by storing more fat for an emergency energy supply as longer, colder nights of midwinter approach.

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