Breeding

Phenology

Pair Formation

Birds found in pairs in winter flocks, but new bonds form during breeding season, suggesting mated pair bonds may form on breeding grounds immediately before nesting begins (Stokes 1950, Coutlee 1967, Tyler 1968, Holcomb 1969a, Middleton 1979). More information needed.

Nest Building

Photoperiod main proximate factor controlling reproductive cycle (Lynch 1970, Middleton 1978), but appearance of flowering composites suspected to stimulate nesting (Stokes 1950, Lynch 1970, Mundinger 1972, Middleton 1979).

First Brood Per Season

Figure 6. From Walkinshaw (1938), Stokes (1950), Berger (1968), Tyler (1968), Holcomb (1969a), Mundinger (1972), Middleton (1979), Peck and James (1987), Jacobsen (1990), Mariani et al. (1993). In e. North America, nesting does not begin until late Jun or early Jul, although a few records of early nests with eggs in May and early Jun. At Guelph, ON, first eggs presumably laid by experienced females, with mean date 6.5 Jul (SD = 1.56; n = 23; range 28 Jun–10 Jul). Nesting peaks in second half of Jul when first-time nesters begin laying. Nesting decreases in Aug, but can continue into Sep in some parts. Last egg date at Guelph, 25 Aug, but 24 Sep recorded as latest date in Ontario.

Elsewhere, nesting dates vary with subspecies. In w. North America, eggs dates for C. t. pallidus fall between 24 May and 18 Aug, with peak of nesting between 20 Jun and 8 Jul; for C. t. jewetti eggs laid between 15 Jun and 6 Jul (Tyler 1968). C. t. salicamans earliest nesting subspecies; season begins late Apr, ends in early Jul with peak in May (Tyler 1968).

Delayed (July) breeding, compared to other species, may be related to availability of suitable plant materials for nesting and composite seeds for feeding young associated with amenable climates of southwest coastal regions. Predation pressure apparently lower late in season in east-central Illinois as well (Peak 2003). Despite late breeding, still become spontaneously photorefractory, both gonadally and neurally (for song-system nuclei), like other songbirds in late summer (Marsh et al. 2002).

Renesting

If early nest destroyed, renesting occurs. At Guelph, ON, time between loss of nest and laying of first egg in replacement clutch averages 6.9 d (SE = 0.42; n = 9; Middleton 1979), but considerable variation elsewhere (Stokes 1950). Most renesting occurred in August at this site (Gissing et al. 1998).

Nest Site

Selection

Pairs move through suitable vegetation, examining, squatting, swivelling, and repeating movements in prospective nest sites, suggesting both sexes involved in selecting nest site (Middleton 1970b). Male frequently observed to “fidget” with suitable nesting materials, as if to stimulate female into building, but material invariably dropped. Final site apparently chosen by female (ALAM).

Microhabitat

From Stokes (1950), Nickell (1951), Lewis (1952), Sutton (1959), Tyler (1968), Holcomb (1969a), Harrison (1978), Miller (1978), Middleton (1979), ALAM. Avoids mature forest and prefers shrubs in early successional growth with clear space on at least one side of nest site. Preferred sites in variety of deciduous shrubs with appropriate, upright, terminal cluster of twigs, beneath canopy. Will nest in wide variety of plants including conifers and herbaceous plants. Nest height varies with habitat, extremes of a few centimeters to several meters reported. Nests frequently clumped in “loose colonies,” but “coloniality” may result from distribution of some resource other than nest site.

Nest

Construction

Built by female alone, accompanied closely by the mate-guarding male (Batts 1948, Stokes 1950, Nickell 1951, Tyler 1968, Lynch 1970, Middleton 1988). Building takes place in spells, alternating with rest periods, throughout day (Batts 1948, Middleton 1970b, unpub.). Nest usually completed in 6 d (Middleton 1979), range 4–15 d (Walkinshaw 1938, Stokes 1950, Tyler 1968, Holcomb 1969a). Rate varies with calendar date, experience of female, and between season (Stokes 1950, Holcomb 1969a, ALAM).

Nest built in 3 stages (see Middleton 1965). First, foundation lashed to supporting twigs with spider silk. Next, compact cup of rootlets and various plant fibres gradually built up and shaped around female’s body. Finally, “downy” lining is added, usually pappus of Compositae, but will use any down available including artificially supplied cotton (Stokes 1950, Nickell 1951, Mundinger 1972, Harrison 1978). Nest materials many and varied (Nickell 1951).

Dimensions

Similar dimensions from various studies: inside diameter 5 cm (range 4.0–8.0 cm); outside diameter 8 cm (range 6.0–10.0 cm); inside depth 3.5 cm (range 2.5–5..5 cm); outside depth 7.2 cm (range 4.5–11.0 cm; Walkinshaw 1938, Batts 1948, Nickell 1951, Holcomb 1969a, Peck and James 1987, Watt and Dimberio 1990).

Microclimate

Nest built in shaded location under canopy of leaves or dense cluster of needles (Batts 1948, Lewis 1952, Peck and James 1987). Though shaded from above, nest often readily visible from below. Nests of such compact construction that they hold water (Lewis 1952, Berger 1968, Holcomb 1969a, ALAM). Compact construction also suggests high insulative value, though no data available.

Nest Abandonment And Reuse

From Stokes (1950), Nickell (1951), Holcomb (1969a), ALAM. Nests sometimes abandoned during construction and before egg laying. Causes may include disturbance, unsuitable site, or wind and rain. Materials from such nests frequently reused in new nest construction. Rarely, some nests apparently reused for rearing a second brood (Peck and James 1987), and by other species (Nickell 1951).

Eggs

Shape

Subelliptical to oval.

Size

Egg dimensions reported by various authors (length x breadth): 16.5 x 12.4 mm (Berger 1968); 16.2 x 12.2 mm (Tyler 1968); and 16.9 x 12.8 mm (Holcomb 1969a).

From Western Foundation of Vertebrate Zoology—for C. t. jewetti : 16.4 (15.3–17.4) x 12.5 mm (11.9–13.2; based on 20 clutches, 114 eggs); C. t. pallidus : 16.88 (16.1–17.6) x 12.7 mm (12.4–13.5; 9 clutches, 38 eggs); C. t. salicamans : 15.9 (15.0–17.0) x 12.2 mm (11.5–12.8; 20 clutches, 93 eggs); C. t. tristis : 16.4 (15.2–17.5) x 12.5 mm (11.9–13.4; 20 clutches, 97 eggs).

Color

Eggs very pale bluish white, usually unspotted but occasionally with faint light brown spots usually concentrated at larger end of egg.

Surface Texture

Eggshell smooth, but not glossy (Harrison 1978, ALAM).

Egg Laying

Precise time of egg laying difficult to establish. Apparently early morning, most between 06:00 and 08:30, and all laid before 10:00 (Walkinshaw 1938, Holcomb 1969a, ALAM). Eggs most commonly laid at 1 d intervals until clutch complete, but exceptions recorded (Peck and James 1987). Largest clutches laid early in nesting season; clutch size decreases as season progresses and in renests or second brood attempts by a single female (Walkinshaw 1938, Stokes 1950, Holcomb 1969a, Middleton 1979).

During egg laying, female spends night on nest and presumably deposits egg before departure next morning. Pair absent from the nest for long periods early in egg laying, but female encountered with increasing frequency at, or near nest, as clutch nears completion. Pair remain near to each other and copulations observed at this time (ALAM).

Intraspecific egg dumping not reliably documented. May explain isolated records of 2 or more eggs being laid in the same nest at same time (Holcomb 1969a).

Incubation

Onset Of Incubation

Incubation by female alone; begins before laying of last egg (Holcomb 1969a, Peck and James 1987, ALAM). Single incubation patch extends posteriorly from division of ventral feather tract to vent, developed only in female; appears with first egg and reaches full development with complete clutch. Incubation period averages 12–14 d, but considerable variation (Berger 1968, Holcomb 1969a, Peck and James 1987). Influenced by experience of female and climatic conditions (Middleton 1979, Jacobsen 1990).

Parental Behavior

Following observations based on 522 h 24 min observations at 25 nests in Guelph, ON (Middleton 1988), and supported by literature. Female incubates for long unbroken spells while fed on nest by male (Mousley 1930, Kendeigh 1952, Linsdale 1957, Tyler 1968, Newton 1972 ). At Guelph, feeding intervals vary from 30 to 90 min with no consistent pattern. Similar to studies elsewhere (Mousley 1930, 1932, Tyler 1968). On nest, female spends time sleeping, preening, and shifting position. Periodically slips off nest for a few minutes then returns to resume incubation (Tyler 1968). Also leaves nest to chase intruders that approach too closely (Batts 1948, ALAM).

Female recognizes call of approaching mate (Mundinger 1970) and responds with high trilling call. As male appears at nest, trilling intensifies and female faces him with crouched posture and fluttering wings (Tyler 1968). Female then fed by regurgitation. When finished feeding, male flies to nearby perch, wipes bill several times, and flies off. Female may fly off with male for a few minutes or perch on nest rim and fluff feathers, before resuming incubation. Whole procedure lasts about 3 min (ALAM).

Incubation Period

Difficult to calculate with precision but 12–14 d appears normal (Berger 1968, Holcomb 1969a, Peck and James 1987). Considerable variation recorded, and incubation known to be influenced by clutch size, experience of female, climatic conditions, and calendar date within season (Holcomb 1967, Holcomb 1969a, Middleton 1979, Jacobsen 1990). Protracted incubation of infertile eggs (Berger 1968).

Hatching

Preliminary Events

No clear evidence, from behavior or vocalizations, when hatching imminent.

Emergence

First signs involve female’s disturbed incubation behavior, frequent standing, peering, and poking into nest. Hatching begins with pipping followed by gradual chipping of broad end, eventual separation of cap, and struggling emergence of chick (ALAM). Hatching of individually marked eggs appeared to require about 15 h (ALAM). Evidence to support both synchronous (< 24 h; Holcomb 1969b, ALAM) and asynchronous (> 24 h; Holcomb 1969b, Newton 1972, Skagen 1987, A.M. Jacobsen pers. comm.) hatching of clutch.

Parental Assistance/Shell Disposal

Not known if female actively assists hatching. Fragments of shell observed to be eaten, and larger fragments removed from nest, by female (ALAM).

Young Birds

Condition At Hatching

Young altricial. Sex ratio unity. Mass of males =1.08 g (SD = 0.051; n = 161): females = 1.07 g (SD = 0.054; n = 145; Jacobsen 1990), comparable to other studies (Holcomb 1968, 1969b). Chicks essentially naked, with few wisps of pale grayish natal down on crown and body. Body reddish with faint dark lines tracing incipient feather tracts. Mouth pinkish red with gape flanges pale yellow (Tyler 1968, Harrison 1978, ALAM). Legs dark. Eyes closed at hatching. Egg tooth disappears within 2 d.

Growth And Development

Young grow rapidly in first few days. At Toledo, OH, body mass of 9.9 g reached on 9th day. Thereafter, weight increase slowed; maximum nestling weight of 12.2 g reached on 14th d (Holcomb 1968, 1969b). Growth of culmen, tarsus, wing, and total body reflect a similar pattern (Holcomb 1968, 1969b). Eyes begin to open around day 3 and fully open by day 7 (Holcomb 1969b).

Feather tracts increasingly obvious, with ensheathed feathers erupting between days 3–6, opening (fringing) between days 5–7 and giving good covering by 9th d (Holcomb 1969b). Alar tract first to project and caudal the last. Flight feathers on wing grow fastest and by 12th d reach 59% adult wing length. Tail feathers, by contrast, short and stubby (Holcomb 1968, 1969b). Juvenal plumage recognizable by 12th d.

Respond quickly to approaching parents. Any vibration at nest causes nestlings to raise their heads and open their gapes, accompanied by faint, high-pitched, begging calls (ALAM). Between 8th and 10th d, begging calls become markedly louder (Knight and Temple 1986). During early brooding, most time spent sleeping in crouched posture. Thereafter, activity increases as preening and stretching become common and progressively less time spent crouching and sleeping (ALAM). Nestlings need 12 d development to survive nest departure (Berger 1968, Newton 1972, ALAM).

Parental Care

Brooding

Over first few days chicks brooded closely by female, while male continues to feed her at nest (Mousley 1930, 1932, ALAM). About 4th d broodiness begins to wane, becoming increasingly limited to early morning hours, cold or rainy periods, and overnight (ALAM). By 8th d brooding apparently not essential and chicks capable of surviving without it (Middleton 1979, 1988).

Feeding

Male continues to feed female on nest; female, in turn, feeds chicks. Around 4th d female begins to leave nest for lengthening periods, both parents now feed chicks directly but male gradually assumes chief responsibility (Mousley 1930, 1932, ALAM). Female’s role in early days post-hatching is critical to nest success. At Guelph, ON, loss of female in first 8 d post-hatching invariably led to nest failure, while loss of male did not (Middleton 1979, Pengelly 1982). Female’s feeding role diminishes as broodiness wanes. By 8th d female can abandon brood without risking its success (Middleton 1979, 1988).

All food is provided in form of a sticky, semi-solid mass primarily of seeds, regurgitated by parents (Newton 1972). No detailed analysis but observations suggest food is similar to that consumed by adults (ALAM). Rates of provisioning vary among pairs, nestling stage, and season. By comparison to other passerine species, feeding rates are slow and vary between 30 min to over 1 h (Mousley 1930, Stokes 1950, Tyler 1968, ALAM). Food apparently distributed among chicks in nest as parents give attention to > 1 chick at each feeding.

Nest Sanitation

Nestling droppings eaten or removed by parents until 7th or 8th d, when feces is voided over edge of nest and begin to accumulate on nest rim (Mousley 1930, Stokes 1950, Nickell 1951, Watt and Dimberio 1990). Nest gradually becomes trampled and at departure is flattened and feces encrusted (Watt and Dimberio 1990). Defecation often follows feeding, particularly in early stages of development.

Feather mites commonly encountered (Nickell 1951, ALAM) and other invertebrates frequently found in used nests (Watt and Dimberio 1990).

Cooperative Breeding

Not known for this species.

Brood Parasitism

In some populations early nests commonly parasitized by Brown-headed Cowbird (Middleton 1977c, 1991, Friedmann and Kiff 1985). Because breeding seasons of these species barely overlap, goldfinch nests begun later than 16 Jul at Guelph, ON, are immune from cowbird parasitism (Middleton 1977c). Incidence of parasitism varies from 0% to 9.4% (Walkinshaw 1938, Stokes 1950, Nickell 1951, Holcomb 1969a, Middleton 1977c, Mariani et al. 1993).

Because incubation begins with penultimate egg, nest seldom left exposed as clutch nears completion. All cowbird eggs encountered, Guelph, ON, were laid immediately before egg laying began or when 1 or 2 goldfinch eggs present. Two cowbird eggs greatest number found in any one nest (Berger 1968, ALAM).

Goldfinches appear tolerant of cowbirds away from the nest. Behavior at the nest not observed. In isolated instances host known to build floor over parasite’s egg (Berger 1968, ALAM). Desertion suspected if cowbird egg is laid before any of host’s eggs, but whether parasitism is primary cause of desertion is difficult to verify (ALAM).

Effect Of Parasitism

Parasitism significantly reduces clutch size, by approximately 1 egg, and most adversely affects experienced nesters (Middleton 1977c). Although most cowbird eggs hatch, few cowbird chicks survive beyond 3 d (Middleton 1991). If cowbirds survive > 3 d, development is retarded; none known to survive in nest > 15 d (ALAM). At Guelph, no records of cowbirds successfully departing goldfinch nests (Middleton 1991). Berger (1968) reported similar observations. This failure apparently caused by insufficient protein in seed diet of goldfinch (Middleton 1991, Mariani et al. 1993). Successful rearing of cowbirds by goldfinches must be a very rare event (but see Friedmann and Kiff 1985).

Where cowbirds survive beyond 3 d, their ability to deprive goldfinch nestlings of food severely restricts development of latter, and usually results in total nest failure (Middleton 1991). Such events are rare and bulk of population little affected by cowbird parasitism. American Goldfinch poor cowbird host.

Fledgling Stage

Nestling Period

Value of nestling period calculations questionable because time of nest departure determined by variety of factors (Middleton 1970b, Newton 1972). At undisturbed nests, departure any time after 12th d (range 11–17 d; Mousley 1930, 1932, Stokes 1950, Berger 1968, Harrison 1978, Newton 1972, ALAM).

Condition At Departure

At departure, chicks have almost completed body growth, with feathers one half to two thirds grown (Holcomb 1969b). Chicks active and alert, and spend much time immediately before departure in preening, stretching, and visually exploring nest vicinity.

Manner Of Departure

At undisturbed nests, surrounded by vegetation, young climb from nest and on to neighboring branches (Mousley 1930, Tyler 1968, ALAM). Because individuals leave at different times, nest departure may be spread over a full day. Observations suggest a preference for the midday period (see Middleton 1965, unpub.). In exposed nests, young capable of sustained flight may fly considerable distance to protective shrubbery (Berger 1968). In first few days, young found dispersed in immediate nest vicinity and located through begging calls (Tyler 1968, ALAM). As flight improves, young begin to follow parents in group.

At disturbed nests, and if nest departure premature, young burst explosively from nest and flutter to ground where they disperse quickly into cover. If capable of flight, brood members fly off in various directions to suitable protective shrubbery (Berger 1968, ALAM).

Dependence On Parents

Young remain dependent on parents for about 3 wk after nest departure, but precise timing of complete independence difficult to determine. Juvenal plumage completes growth during first week. As flight capability improves, family group becomes mobile and ranges over wider area. Group maintained by chick calls given from stationary locations and during flight. During first week young begin to pick and probe at various items and gradually begin to forage for themselves. Young respond quickly to parents approaching with food by flying to meet them with loud begging calls. Young appear to harass parents for food, and compete with siblings through vigorous begging display (ALAM).

Where female produces second brood, male usually assumes full responsibility for chicks from first nest (Middleton 1979, 1988).

Immature Stage

Following independence, immature birds collect into flocks, often associated with adult birds, characteristic of late summer and early autumn. Such flocks gradually increase in size; by late Sep to early Oct they may number in the hundreds. Flocks roam countryside in search of food, which tends to be abundant at this time of year. Many young remain in the northern parts of the range during winter (Prescott and Middleton 1990), gradually completing their First Prealternate molt (Middleton 1977b, 1978). Breeding condition is achieved by mid- to late Jun of next year (Mundinger 1972, Middleton 1978). Young birds enter breeding population in first year, but achieve breeding condition about 2 wk later than adults (Middleton 1978). Accordingly, they nest later than experienced birds (Middleton 1979).