Food Habits

Feeding

Main Foods Taken

Winter: small seeds, primarily grasses. Breeding season: small seeds, adult and larval insects (Judd 1901, Martin et al 1951).

Microhabitat For ForagiNg

Winter: Forages on ground or low-lying vegetation (< 1 m), primarily in open grassy or brushy fields. In central N. Carolina, favors fields dominated by crabgrass (Digitaria sanguinalis) or horseweed (Leptilion sp.); moves to other fields if seeds on such sites depleted (Pulliam and Enders 1971). Shows preference for food patches nearer protective cover (Pearson 1991, Beck and Watts 1997). Summer: forages on ground or low-lying vegetation (< 1 m) within the breeding territory (Evans 1964, Allaire and Fisher 1975).

Food Capture And Consumption

Feeds alone or with mate in the breeding season (MC); small flocks in winter. High quality food patches of larger size lead to larger flocks and to larger individual distances (Pearson 1989, 1991). Feeds directly on fallen seeds or flies to the tops of grasses, letting weight carry stems to the ground; then begins removing seeds. Scans vegetation for insects from a perch 30–40 cm high and pounces on any seen; no single perch used for more than 10 s. Foods eaten as found; seeds husked with beak and tongue; insects generally swallowed whole (Allaire and Fisher 1975).

Diet

Major Food Items

Winter: > 90% of food items found in analyses of gut contents were seeds, virtually all from various grasses. With approach of spring and through the summer, the proportion of plant food in diet declines. Grass seeds are <50% of the summer diet; insects the rest; seed proportion rises once again from August through fall (Judd 1901, Martin et al. 1951, Evans 1964, Pulliam and Enders 1971, Allaire and Fisher 1975). Small beak (see Measurements) correlates with small sized seeds: mean size (length x width x height)1/3 = 2.4 mm (Pulliam and Enders 1971); mass of individual seeds = 0.003–0.006 g (Willson 1971). No data on diet changes over the course of the summer breeding season.

Quantitative Analysis

As seen in Table 1, in Nacogdoches County, Texas, the primary plant food in all seasons was crabgrass (Digitaria sp.) seeds, especially so in summer and winter. The fall plant diet was more varied with panic grass ((Panicum sp.) and foxtail seeds (Setaria sp.) also included. Insect food was mainly Lepidoptera and Coleoptera, with pronounced specialization on Lepidoptera in the fall (Allaire and Fisher 1975).

Near the George Reserve in se. Michigan (studied only in spring and summer), seeds were found in all gizzards collected in spring, but only in half of those collected in summer. Primary seeds were grasses, but in contrast to the Texas study above, no crabgrass. The insect diet was also more varied than that seen in Texas (Evans 1964).

Both of the above diet studies and others (e.g. Pulliam and Enders 1971) suffer from very small sample sizes (see Table 1) and small sampling areas. Feeding ecology of Field Sparrows remains in need of study.

Food Selection And Storage

No data.

Nutrition And Energetics

No data.

Metabolism And Temperature Regulation

Existence energy (M = kcal/bird/d) linearly correlated with temperature (T = ° C) for winter acclimatized birds (males: M = 15.59–0.285T; females: M = 14.69–0.2617T). A curvilinear correlation for summer acclimitized birds (males: M = 16.40 + 0.0001T3–0.0002T2–0.3662T; females: M = 15.87 + 0.0036T2–0.3911T). Lower limit for temperature tolerance under winter photoperiods -13 to -14° C. Upper limit under summer photoperiods 41° C. Coefficient of food utilization (metabolizable energy/gross energy intake) varies from 0.71–0.86; higher values under summer conditions (Olson and Kendeigh 1980).

Drinking, Pellet-Casting, And Defecation

No data.