Behavior

Locomotion

Hops on ground or branches; does not “double scratch” while feeding (Clark 1970). Flight is direct (Fig. 3). Female often gives fluttering moth-like flight when approaching nest before dawn during egg laying (DEB).

Self-Maintenance

Preening, Head Scratching, Bathing, Anting

No detailed descriptions.

Sleeping, Roosting, Sunbathing

Sleep in small trees or leafy shrubs; roost in similar areas in autumn (Walkinshaw 1968a). Female sleeps on nest during incubation; occasionally during egg laying (DEB).

Agonistic Behavior

Physical Interactions

Often reported as less aggressive than other passerines (Walkinshaw 1968a, Fretwell 1970), but males chase conspecific males that enter their territories; occasionally involving midair contact, grappling with beak and legs, and tumbling to the ground (Walkinshaw 1968a, MC).

Communicative Interactions

Fretwell (1970: 47) reports a territorial chase that ended “with both birds making a display of their head and/or neck, assuming in the process a very exaggerated stretched out position with much swaying.”

Spacing

Territoriality

Nature and extent of territory: Male must possess an all-purpose exclusive territory to attract a mate. Territories may be contiguous and tightly packed. Mean size in Illinois was 0.76 ha, range 0.31–1.62 ha; larger territories associated with open grassland (Best 1977b).

Manner of establishing and maintaining territory: Upon return in spring, males advertize presence on territory with Simple Song and directly chase intruding conspecific males outside the boundaries (Walkinshaw 1968a, DAN).

Establishment of boundaries between neighbors associated with long (can last up to 2 h) circular chases around the disputed area. Usually the chased male is the longer established male. Chases are at less than maximum speed, circling in the air or flying from perch to perch closer to the ground. Typically, after a period of < 1 min, both males will perch and sing (often Complex Song in this context) or feed; chase resumes when one bird supplants or flies by the other (MC).

Interspecific territoriality: No routine exclusion of other species from the territory.

Winter territoriality: None.

Dominance hierarchies: No data.

Individual Distance

Individuals in migrating or wintering flocks seen within several meters of each other. In captive flocks, distance between birds ranges from 13.0–29.8 cm, depending on food patch size and flock size (Pearson 1991). Mated pairs may feed very close together (Walkinshaw 1968a).

Sexual Behavior

Mating System

Almost exclusively monogamous, pairing with 1 mate at a time. Central Illinois—all monogamous (Best 1977b, 1979); s. Michigan—all monogamous (Evans 1976, 1978). In Pennsylvania, of 436 territorial males, 392 (90%) monogamous, 5 (1%) polygynous, 39 (9%) acquired no mate (Carey 1990, MC).

Pair Bond

Male follows female closely during nest building and egg-laying periods, 7 such pairs were observed for a total of 210 minutes in PA in 2006. Male was <5 m from female 88% of the time and >20 m from female only 4% of the time. Outside of the above nesting periods, male does not accompany female (MC). Simple Song rate decreases greatly once female appears (MC). Walkinshaw (1968a) observed that males will aggressively fly at and chase newly arrived females. Within a few hours such chases cease; males then accompany females and chase other males away. Only rare observations of courtship feeding (MC).

Precopulatory displays, copulation, and postcopulatory displays: Copulatory behavior starts during nest building, 2–5 d prior to laying the first egg. Female crouches horizontally with tail raised, usually on a low branch, flutters wings, and gives Ti-ti-ti Call. Male approaches from above rear, often with Rapid High-pitched Trill, mounts female, and makes vent contact for about 2 s. Male then flies some distance away. Both birds often chip and engage in vigorous preening following copulation. Within 1–2 d of egg laying, pairs often observed copulating 2–3 times/min over a period of a few minutes (Walkinshaw 1968a, MC).

Duration and maintenance of pair bond: Females appear to pair within 1–2 d of arrival and typically remain with their mates for a breeding season (Evans 1976, 1978). ). In Pennsylvania (1987-2006), 199 of 379 males (53%) paired at beginning of the breeding season remained paired to the same female throughout (MC). No apparent trend in annual variation in season-long pairings over the course of the study (MC). In Illinois, pair bonds appeared less long lasting: 23 males experienced 23 mate desertions in 1972 (Best 1977b). Desertions typically follow nest predation or parasitism (Best 1977b, MC), but in Pennsylvania (1991–1992) 23 of 40 desertions occurred shortly after fledging young (MC). Mates rarely pair once again in the following year. In Pennsylvania, of 312 pairs together at the end of the breeding season (1987-2005), only 17 (5.5%) remated in the following year (MC). Given annual return rates of adults (see Lifespan and Survivorship below), this proportion is much less than would be expected if surviving mates always paired again with each other.

Extra-Pair Copulations (EPCs)

MC observed no EPCs over 7 yr in Pennsylvania. Petter et al. (1990) observed 1 EPC in 700 observation hours in Ohio. Walkinshaw (1968a) observed a single female copulating with 3 males. In Pennsylvania, DNA fingerprinting indicated that 23 of 152 (15.1%) nestlings so far analysed had DNA that did not match the attending male (MC). Petter et al. (1990), using protein comparisons, found that 5 of 52 (10%) nestlings had proteins mismatched with the attending male, though 3 might have been intraspecific brood parasitism.

In Pennsylvania (1990-2002), DNA fingerprinting indicated that 98 of 1,051 nestlings (9.3%) had DNA that did not match the attending male. 36 of 175 sampled males (20.6%) had at least one extra-pair nestling in their nests (MC). 82 of the 98 extra-pair nestlings (84%) were in nests in which virtually the entire brood was extra-pair. There were 18 males attending such nests, and 13 (72%) of them were first time breeders on the site; 78% of their social mates were also first time breeders on the site. Such cuckolded males and their social mates were also likely to have been late arrivals in spring migration (MC).

In Pennsylvania (1990-2002), the frequency of EPCs steadily declined from 20% in 1990 to 0% in 2000-02. This decline in frequency was highly correlated (r = 0.77, df = 11, p = 0.002) with the decline in breeding population size on the site over those years (see Demography and Populations below) (MC).

Social And Interspecific Behavior

Degree of sociality

Solitary during the breeding season. Small flocks in winter and migration. Mated pairs may feed in close proximity to other pairs on spaces between territories with no signs of aggression (Walkinshaw 1968a).

Play

Independent young 25–30 d old observed diving and flying at each other. Walkinshaw (1968a) interpreted this as play.

Nonpredatory interspecific interactions

A Field Sparrow and a Rufous-sided Towhee (Pipilo erythrophthalmus) pair nested 0.45 m apart; both species fed young at both nests (Hoyt and Southgate 1948). A Field Sparrow and a Common Yellowthroat (Geothlypis trichas) laid and incubated full clutches in the same nest (MC). No data on winter flocking with other species. Isolated Field Sparrows seen occasionally in ne. Pennsylvania typically found with wintering American Tree Sparrow (Spizella arborea) flocks (MC).

Predation

Kinds of predators and manner of predation

Adult birds disappear, but cause not usually known; brooding females, eggs, and nestlings are taken, usually by unknown predators. Eggs and nestlings usually all taken at once (Best 1978).

Thompson and Burhans (2003) used video cameras to record nest predation events. Of 46 predators identified in Field Sparrow habitat, 33 (72%) were snakes, with 40% of the events due to black rat snakes (Elaphe obsoleta). Other predators were mainly mammals and raptors. Blue racers (Coluber constrictor) observed taking nestlings (Best 1974c, DEB). Naumann (1929) observed a rattlesnake (species not reported) taking adult and nestlings. Walkinshaw (1968a) observed a milk snake (Lampropeltis sp.) taking eggs. Other snake predators include garter snake (Thamnophis sirtalis), and prairie kingsnake (Lampropeltis calligaster; Best 1978, DEB, MC). Snake predation generally thought to leave nest undisturbed; sometimes with a hole in the bottom (Best 1978, Nolan 1978, Thompson and Burhans 2003, MC). Using this pattern, Best (1978) attributed 48% of 403 egg losses and 54% of 137 nestling losses to snakes; MC attributed 62% of 377 predated nests to snakes.

Nolan (1963) observed a chipmunk (Tamias striatus) remove and eat a nestling. Other mammalian predators are thought to include red fox (Vulpes fulva), gray fox (Urocyon cineoargenteus), weasels (Mustela spp.), skunks (Mephitis mephitis), mink (Mustela vison), raccoon (Procyon lotor), and opposums (Didelphis virginiana; Best 1978, Evans 1978, Thompson and Burhans 2003). Nests pulled from the vegetation are thought to be a result of mammal or raptor predation (Thompson and Burhans 2003).

Birds seen destroying nests include Blue Jays (Cyanocitta cristata; Walkinshaw 1968a) and house wrens (Troglodytes aedon; Crooks and Hendrickson 1953, Thompson and Burhans 2003). American Crow (Corvus brachyrhynchos) observed eating nestlings (Batts 1958).

Response To Predators

Adults take cover when accipiter hawks are nearby (Walkinshaw 1968a). Adults give rapid chip calls when humans are near nest; chips also heard in response to blue racers at nests (Sutton 1960, DEB). No physical attack on predators. Adults with fledged young feign wing injury when approached by humans (Crooks 1948, Batts 1958, DEB, MC).