Breeding

Few data; see Figure 5 . Approximate length of breeding period near Juneau, se. Alaska: 3 mo (Rogers 1994). Cloacal protuberance and brood patches present from Apr through Aug (Pyle 1997). Testes and ovaries enlarged and brood patch partially defeathered beginning as early as Apr (museum specimens LSUMNS, UWBM). Arrives on breeding grounds from early Apr through early May, often before snow has melted (see Migration, above; Philipp 1925).

Pair Formation

In Newfoundland, most pairs arrived during first 2 wk of Apr; male establishes territory and, within a week after arrival, establishes a pair bond (Blacquiere 1979, Threlfall and Blacquiere 1982).

Nest-Building

Nests of P. i. schistacea usually built in 2–3 d, but in one instance, a pair constructed an entire nest in 1 d and female laid first egg in nest that evening (Bendire 1889). Female puts final touches on nest, adding inner lining (Bendire 1889). Apparently, in P. i. megarhyncha, female is sole nest builder (Mailliard 1921).

First/Only Brood Per Season

Egg-laying. Few data; 2–5 eggs laid starting from early May through Jun and even into early Jul (Bendire 1889; Pierce 1921; Linsdale 1928a; Austin 1932, 1968; Terrill 1968; Threlfall and Blacquiere 1982; Peck and James 1987; Rogers 1994). In Newfoundland, onset of laying relatively constant from late Apr to mid-Jun, then drops off, with no laying after 5 Jul (Threlfall and Blacquiere 1982). For 10 wk, starting 27 Apr in Newfoundland, distribution of number of nests in which laying started was as follows: 6, 8, 2, 4, 7, 6, 7, 2, 1, 1. One egg laid/d (Pierce 1921, Ryan 1974).

Hatching of First Chicks. No data. However, given incubation period and egg-laying dates, occurs mid-May to late Jul.

Departure of Young From Nest or Cessation of Close Parental Care. In Newfoundland, some young have already fledged by 1 Jun (Terrill 1968). On west coast of James Bay, first fledglings seen 22 Jul; between 22 Jun and 3 Jul, on the northshore of the Gulf of St. Lawrence, many young fledged and being fed by parents, others no longer under parental care (Terrill 1968). Nestling period (hatching to departure from nest) approximately 10.5 d for one nest at Bonavista, Newfoundland (Ryan 1974). For this same nest, time from laying of first egg to young leaving nest: 26 d (Ryan 1974).

Second/Later Broods Per Season

Little information; no records of double-brooding. However, long breeding period and observations of fresh eggs late in nesting season (late Jun), when many young have already fledged, suggest that P. i. iliaca, P. i. schistacea, and P. i. townsendi may lay second broods (Bendire 1889, Philipp 1925, Linsdale 1928a, Terrill 1968, Rogers 1994). In Newfoundland, no evidence of double-brooding (Threlfall and Blacquiere 1982). P. i. fulva, a member of the megarhyncha group, ap-parently rears only 1 brood/breeding season (Bendire 1889). Studies of color-marked birds needed.

Selection

No information.

Microhabitat

Across entire range, nests on ground, in bushes, or even low trees (Bendire 1889, Harrison 1979, Austin 1968, Terrill 1968, Threlfall and Blacquiere 1982, Burns and Hackett 1993). In Newfoundland, commonly nests in or under coniferous trees or among the roots of upturned stumps (Linsdale 1928a, Terrill 1968, Threlfall and Blacquiere 1982). Of 2 ground nests recorded in Ontario: 1 at base of a moss (Sphagnum sp.) hummock, 1 under a small black spruce (Peck and James 1987). Of 6 P. i. megarhyncha nests found on ground, all were concealed by vegetation: Douglas fir (Pseudotsuga menziesii) seedlings (n = 2), a thicket of chinquapin (Castanopsis sp.; n = 1), leaning limb of an oak (Quercus sp.; n = 1), deer brush (Ceanothus sp.; n = 1), and a piece of lodged bark (n = 1; Mailliard 1921). Of 14 ground nests found in Fresno Co., CA, by Burns and Hackett (1993), however, none was located under conifers.

Nests built in trees or bushes often placed in crotches, elbows, or other such supports (Terrill 1968). Of several nests described from e. Canada, 1 was built on a dead branch leaning against a small spruce, 2 were in the elbows of deformed white spruce (Picea glauca), and one was in the crotch of a yellow birch (Betula alleghaniensis; Terrill 1968). At Lake Tahoe, CA, 3 of 14 P. i. megarhyncha nests were in deer brush in or on edge of a thicket; 1 was in a crotch formed by a 5-cm shoot and the main trunk of a willow; 1 was in a mass of dead branches and debris under a willow clump; and 1 was on a dead aspen (Populus spp.) branch over a small stream (Mailliard 1921). Regardless of where nests are built, they are usually well concealed (Austin 1968, Burns and Hackett 1993). In Sequoia National Forest, 7.5 km west of Hume, Fresno Co., CA (boundary between P. i. stephensi and P. i. megarhyncha), of 23 Fox Sparrow nests found, 40% were completely concealed, 32% were only 25% visible, 12% were 50% visible, and 16% were completely visible without moving any branches (Burns and Hackett 1993). On average, these nests were placed 85 cm from nearest edge of nest plant and 84 cm from top of nest plant (Burns and Hackett 1993).

Site Characteristics

Some specific nest heights from Canada: 1 at 0.6 m, 2 at 1.5 m (Austin 1968), and 1 at 1.8 m above ground (Ryan 1974). Nests also found much higher, including some as high as 6 m (Philipp 1925, Linsdale 1928a, Terrill 1968, Threlfall and Blacquiere 1982). In St. John’s, Newfoundland, 1 of 46 nests was 6 m off the ground, 45 were ≤2.7 m; of these 45, 24 (53%) in trees, 21 (47%) on the ground (Threlfall and Blacquiere 1982). Later nests significantly lower to ground than earlier ones, a change that may be related to snow cover (Philipp 1925, Threlfall and Blacquiere 1982). Some specific nest heights from Hume, Fresno Co., CA (near boundary of P. i. stephensi and P. i. megarhyncha): 14 out of 23 nests (61%) placed on the ground, mean height of above-ground nests (n = 9) 30 cm ± 10.8 SD, mean height of nest plants 1.41 m ± 0.66 SD (Burns and Hackett 1993).

Nest placement within habitat varies geographically. In Newfoundland, most nests were placed under conifers; Fox Sparrows from Gull I., Newfoundland, nested in a climax forest of balsam fir, black spruce, and white spruce (Threlfall and Blacquiere 1982). In Hume, Fresno Co., CA, however, no nests were placed in or under conifers (Burns and Hackett 1993).

Nest-site habitat characteristics of Fox Sparrows in w. North America are quite different from those in the East. Preferred nest sites consist of chaparral with dense shrubby vegetation for concealment (Burns and Hackett 1993; see Habitat: breeding range, above). Rather than choosing nest sites based on species of plants present, it appears that Fox Sparrows focus on more general habitat characteristics such as presence of dense shrubby vegetation for concealment of nests from predators (Burns and Hackett 1993).

Construction

Little information, but female appears likely to construct the nest alone (Mailliard 1921, Burns 1988). Two to 3 d needed to construct a nest, but in one instance, a pair built an entirely new nest between sunrise and sunset of the same day (Bendire 1889).

Structure And Composition Matter

From Bendire 1889, Philipp 1925, Terrill 1968, Ryan 1974, Threlfall 1979, Threlfall and Blacquiere 1982, and others as noted. Nests of northern and eastern iliaca group composed of a wide variety of materials. Outer wall or rim of nest constructed from small twigs (often black spruce or balsam fir), shredded wood, rotting wood, broom moss (Dicranum sp.), strips of bark (sometimes dry and scaly), course dry grasses, mosses (Polystrichum sp. and Sphagnum sp.), lichens (Alectoria sp. and Usnea sp.), and reindeer moss (Cladonia rangifera). Inner cup or nest lining composed of an assortment of materials including fine dead grass, rootlets, hair (from sheep [Ovis aries], cow [Bos taurus], dog [Canis familiarus]), feathers, lichens (Alectoria sp.), moss, and monofilament fishing line. Nest composition and structure varies with nest placement: Tree nests bulkier and heavier (mean mass 49.6 g [range 39.0–59.7, n = 5]) than ground nests (mass 9.8 g, 15.2 g [n = 2]; Threlfall 1979, Threlfall and Blacquiere 1982). Nests in trees have outer wall of black-spruce twigs, rotting wood, lichens, and moss with inner cup of dead grass. Ground nests built from dead grasses are set into a depression that supports sides of nest. Inner linings of ground and tree nests similar.

In w. North America, members of the schistacea, megarhyncha, and unalaschcensis groups construct nests from materials similar to those used by members of the iliaca group (Bendire 1889, Grinnell 1910, Mailliard 1921, Austin 1968, Harrison 1979, Burns and Hackett 1993).

Dimensions

A nest from Moose Factory, Ontario (U.S. National Museum 4411) measured 12.7 cm wide × 7.62 cm deep on outside and 7.62 cm wide × 5.08 cm deep on inside (Bendire 1889). In Fresno Co., CA (boundary between P. i. stephensi and P. i. megarhyncha): mean of outside diameter 6.9 cm ± 1.2 SD; outside height 6.7 cm ± 1.2 SD; depth 4.8 cm ± 0.9 SD (n = 23; Burns and Hackett 1993). Nest size varies regionally, but pattern is unclear. Nest dimensions from other localities include: San Bernadino Mtns., CA (P. i. stephensi; average in cm, n = 4), outside diameter 15.2, inside diameter 7.6, outside depth 11.4, inside depth 4.4 (Pierce 1921); Lake Tahoe, CA (P. i. megarhyncha; range in cm, n = 14), outside diameter 15.2–35.5, inside diameter 6.3–7.6, outside depth 7.6–13.9, and inside depth 2.5–4.4 (Mailliard 1921).

Microclimate

No data.

Nonbreeding Nests

Before first clutch is laid, may build >1 nest (Threlfall and Blacquiere 1982). Will abandon first nest and build a second to renest if first clutch is destroyed (Threlfall 1979, Burns 1988).

Shape

Oval (Grinnell 1910, Harrison 1979).

Size

Mean length and breadth, in mm: iliaca from Newfoundland, 23.5 ± 0.84 SD × 17.1 ± 0.50 SD (n = 20; Threlfall and Blacquiere 1982); stephensi, 22.08 ± 1.08 SD × 17.06 ± 0.86 SD (n = 17; Pierce 1921). A lack of published egg-measurement data including standard deviations makes assessing patterns of geographic variation in egg size difficult.

Mass

Mean mass of P. i. iliaca eggs from Newfoundland: 3.5 g ± 0.20 SD (n = 21; Threlfall and Blacquiere 1982), about 10% of female body mass.

Color

Slightly glossy; pale bluish green, boldly marked with spots, blotches, cloudings of reddish brown; considerable variation in pattern and color (Pierce 1921, Harrison 1979). Ground color occasionally obscured by brownish markings (Bendire 1889). In Newfoundland, brown spotting tends to be concentrated on larger end of egg (Blacquiere 1979).

Surface Texture

Slightly glossy when laid, but gloss fades with time (Blacquiere 1979).

Eggshell Thickness

No information.

Clutch Size

Mean clutch size in Newfoundland: 3.24 ± 0.60 SD (range 2–4 [n = 34]; Threlfall and Blacquiere 1982). Two out of 50 P. i. schistacea nests examined by Bendire (1889) had 5 eggs. Mean clutch size for P. i. townsendi, near Juneau, AK: 4.11 ± 0.33 SD (n = 9; Rogers 1994).

Egg-Laying

Begins immediately after nest is complete (Threlfall and Blacquiere 1982). Eggs typically laid 1/d, early in morning (Blacquiere 1979).

Onset Of Broodiness And Incubation In Relation To Laying

No evidence of incubation before third, and final, egg laid in one nest observed near Bonavista, Newfoundland (Ryan 1974). Threlfall and Blacquiere (1982), however, collected data from 8 nests and noted that at least 1 female started to incubate before clutch was complete. Incubation by female P. i. megarhyncha also begins as soon as first egg is laid (Mailliard 1921).

Incubation Patch

Only female develops a brood patch, Apr–Aug (Pyle 1997).

Incubation Period

About 12–14 d (Bendire 1889; Austin 1932, 1968; Terrill 1968; Blacquiere 1979; Harrison 1979). Range roughly equal for all 4 groups of Fox Sparrows. In Newfoundland, incubation period for 1 clutch: 12 d 4 h (Threlfall and Blacquiere 1982); 14 d for 3 nests studied near Bonavista, Newfoundland (Ryan 1974).

Parental Behavior

In Newfoundland, incubation performed solely by female (Philipp 1925, Threlfall and Blacquiere 1982). In Hume, Fresno Co., CA, Burns (1988) observed only nonsinging birds, which he assumed to be female, incubating. Most likely for other populations, females are also sole incubators (Mailliard 1921, Austin 1968).

Preliminary Events And Vocalizations; Shell-Breaking And Emergence

Details in Blacquiere 1979 . Small area of shell is cracked and pipped. Once opening exists, chick makes weak vocalizations. Using egg tooth, breaks egg in a narrow line around larger end, near equator. Eventually, top of egg breaks off and chick emerges. Hatching relatively synchronous, all eggs hatching within 35 h of one another (Threlfall and Blacquiere 1982).

Parental Assistance And Disposal Of Eggshells

No eggshells found in nests with newly hatched nestlings, suggesting parents dispose of eggshells quickly (Blacquiere 1979).

Condition At Hatching

P. i. megarhyncha, at about 3 d old are helpless and downy (Austin 1968). P. i. iliaca, from Newfoundland, hatch out with a proportionately larger tarsus than Hume, CA, birds (Burns 1993). Plumage at hatching (natal down) not described (Terrill 1968).

Hatchling mean mass: P. i. iliaca, from Newfoundland, 3.2 g (n = 4; Blacquiere 1979); Hume, CA (where P. i. stephensi and P. i. megarhyncha meet), 2.4 g (n = 4; Burns 1993).

Growth And Development

From Burns 1993 and others as noted. Nestlings grow rapidly (growth constant k = 0.57), with differential growth of particular morphological features favoring early devel-opment of legs and feet (Blacquiere 1979). Relative growth of tarsus length in relation to body mass is allometric; changes throughout development. Comparing populations in Newfoundland (P. i. iliaca) and Hume, CA (where P. i. stephensi and P. i. megarhyncha meet), relative growth rates differ early in development, but eventually converge (see Burns 1993 for details). By the time young leave nest, they are well feathered (Terrill 1968). Juvenal plumage apparently acquired by a complete postnatal molt and resembles a first-winter plumage, but is browner with paler edgings, more streaks above, and heavier dusky streaks below (Dwight 1900; see Appearance, below).

Brooding

Nestlings apparently brooded only by female (Blacquiere 1979, Threlfall and Blacquiere 1982).

Feeding

Female apparently does most feeding of nestlings, but males recorded occasionally carrying food to young (Philipp 1925, Austin 1968, Terrill 1968, Blacquiere 1979, Burns 1988). Males also recorded passing food items to female, who then feeds them to nestlings (Grinnell et al. 1930, Austin 1968). Male recorded feeding one of its young 21 d after offspring fledged (Blacquiere 1979).

Young fed at intervals of 2–5 min (Linsdale 1928a). Parent gathers food from forest-floor litter. Grinnell et al. (1930) observed and collected several adults gathering insect food for young, including one individual that carried 2 large ants and a caterpillar in its bill. Nestlings probably fed primarily animal matter (Linsdale 1928a, Blacquiere 1979). See Food habits: diet, above, for further details.

Nest Sanitation

Parents keep nest “scrupulously clean” (Philipp 1925). Female eats fecal sacs of her nestlings as sacs are voided (Linsdale 1928a, Grinnell et al. 1930).

No information.

Identity Of Parasitic Species

Infrequently parasitized by Brown-headed Cowbirds (Molothrus ater; Friedmann 1963). Brown-headed Cowbird eggs and young found in nests of several Fox Sparrow subspecies, including zaboria, olivacea, schistacea, swarthi, fulva, and monoensis (Bendire 1889, Austin 1968).

Frequency Of Occurrence, Seasonal Or Geographic Variation

Although Brown-headed Cowbirds were common in Fresno Co., CA, Burns (1988) did not find any cowbird eggs or young in Fox Sparrow nests (n = 23). No cowbird eggs found in 9 P. i. townsendi nests observed throughout breeding season near Juneau, AK (Rogers 1994). In the East, Fox Sparrow not parasitized by Brown-headed Cow-birds because ranges do not overlap (Terrill 1968).

Timing Of Laying In Relation To Host’s Laying

No information.

Response To Parasitic Mother, Eggs, Or Nestlings

No information.

Effects Of Parasitism On Host

No information.

Success Of Parasite With This Host

No information.

Departure From Nest

As early as beginning of Jun (Todd 1963, Austin 1968, Terrill 1968). Near Juneau, AK, last nestling fledged by 2 Jul (Rogers 1994).

Age at Departure. Nine to 10.5 d between hatching of young and departure from nest (Ryan, 1974, Blacquiere 1979).

Condition of Development at Departure. In some cases, fledglings unable to fly (Blacquiere 1979).

Manner of Departure. When young nearly ready to leave nest, they jump out and hop away (Blacquiere 1979).

Growth

From Blacquiere 1979 . Nestling body mass at fledging: 25–26 g (about 64% of adult mass). Of 8 body parameters measured in P. i. iliaca from Newfoundland, only tarsus reached full adult size prior to fledging. At fledging, measurement of length of hallux plus claw was 83% of adult size; all other body parameters <75% of adult size.

Association With Parents Or Other Young

Once young leave nest, they are accompanied by parents; one color-banded adult male P. i. iliaca, still on its territory 21 d after its nestlings fledged, fed one of its fledglings (Blacquiere 1979). In Aug, family groups observed with fully fledged young (Austin 1968).

Ability To Get Around, Feed, And Care For Self

No information.

In comparison to other passerines, skulls of Fox Sparrows pneumatize slowly (Stewart 1972). Skull pneumatization completes as early as 1 Dec, but some second-year birds may retain unpneumatized ‘windows’ on top of the skull through summer and rarely into fall (Pyle 1997). In most cases, window in skull retained longer than the Bursa of Fabricius (LSUMNS, UWBM). In one case, however, a bird with a completely ossified skull and a 6 × 4-mm granular ovary had a 5 × 4-mm bursa (UWBM).