Breeding

Pair Formation

Timing is uncertain; probably winter–early spring. Males perform courtship displays for several months, beginning Dec–Jan. Pairs are observed in late winter (Jan–Mar) on coast of British Columbia (JME). Courtship activity in Sweden occurs from Dec to May (Johnsgard 1978). Nearly 80% of adults were paired when they arrived on breeding grounds in New Brunswick (Cartar 1958).

Nest-Building

Begins with onset of egg-laying and follows same phenology.

First/Only Brood Per Season

See Figure 4 . Single brooded. Nest initiation dates in central British Columbia range from 4 Apr to 1 Jun (median date 4 May, 159 nests, 1984–1993; JME). Hatching of first British Columbia chicks 21 May–10 Jul (median date 14 Jun, 109 nests; JME). Near Kirkland Lake, Ontario, nest initiation dates range from 16 Apr to 26 May (median date 7 May, 96 nests, 1974–1979) and hatch dates from 3 May to 1 Jul (median date 17 Jun, 36 nests; HGL). Initiation dates for nests near Sudbury, Ontario, range from 24 Apr to 27 May (median date 11 May, 60 nests) and hatch dates from 23 May to 6 Jul (median 13 Jun, 38 broods; MLM). In Minnesota, nests are initiated in mid- to late Mar, hatch 23 May to 17 Jul (median date 14 Jun, 155 nests; M. C. Zicus unpubl. data). Nest initiation in Maine is from mid-Apr to 8 May (Gibbs 1961). In New Brunswick, initiation dates range from 7 Apr to 31 May, with peak 11–20 May (Cartar 1958, Prince 1965). On Athabasca Delta in Northwest Territories, nesting begins mid-May, downy young first observed 16 Jun (Bellrose 1980). Nest initiation date is positively correlated with date of ice break-up on main breeding lakes in Ontario (HGL); negatively correlated with age of female in British Columbia and Ontario (older females breed earlier; Mallory et al. 1994, JME). Hatch date in Minnesota varies significantly among lakes and years, owing to lake characteristics and date of ice break-up (M. C. Zicus pers. comm.).

Selection Process

Females with breeding experience are generally faithful to previous nest sites (Dow and Fredga 1985, MLM, JME, HGL); females with no previous breeding experience usually group together and prospect for potential nest cavities the summer before a nesting attempt (Eadie and Gauthier 1985). Prospecting females may also include birds that failed in a current breeding attempt and hens that successfully reared a brood (Zicus and Hennes 1989). When using nest boxes, females prefer boxes occupied in the previous year (Dow and Fredga 1985, MLM, JME). Successful nests are visited more frequently by prospecting females in Minnesota (Zicus and Hennes 1989). When several suitable nest boxes are available, females prefer those situated on wetlands with abundant aquatic invertebrates (usually fishless) and on wetlands relatively isolated from others (Mallory et al. 1993), although they will use boxes near others in clusters (several per kilometer; Dow and Fredga 1985, MLM).

Site Characteristics

Cavity nester; uses live or dead trees (apparently uses most tree species), but infrequently will attempt to nest in other sites such as rock crevices (Bellrose 1980, Western Foundation of Vertebrate Zoology [WFVZ] unpubl. data). Nests in natural cavities may be at shoreline or up to 1.3 km away from water (WFVZ); nest types include holes formed by Pileated Woodpeckers (Dryocopus pileatus) or by broken tree limbs, and hollow tops of standing trees (“chimneys”; Bellrose 1980). Recorded heights to entrance holes range from 1.3 to 13 m, although some are reported at or close to ground level (M. C. Zicus pers. comm., JME). Females using nest boxes prefer those lined with wood shavings and dark interiors (Lumsden et al. 1980, 1986); may prefer boxes placed high off ground (Dow and Fredga 1985, Lumsden et al. 1986), perhaps to minimize predation.

Construction Process

Female constructs and maintains nest; nesting material is preferred but not necessarily added. Female creates a nest bowl in the material already in nest cavity (wood chips, old squirrel nests) and lines it with downy feathers from her breast (deposited after initiation of egg-laying; Lumsden and Wenting 1976).

Dimensions

Prince (1968) reported 16 nests in New Brunswick with average interior diameter 20.6 cm (SD 4.1), depth 46.2 cm (19.6) (depth of nest can range from 20 to 120 cm [WFVZ] 47 nests]), and entrance hole 22.4 cm (16.3) long by 11.4 cm (3.6) wide. Nest-box data suggest that cavity orientation is not important in site choice but that boxes should be at least 33 cm deep with entrances 13 x 10 cm and floors >19 cm in diameter (Lumsden et al. 1980).

Microclimate

Nest-cavity temperatures may reach 34.6°C; average difference in daily minimum and maximum was 4.5°C for one female monitored in Finland; relative humidity ranged between 48 and 93% (Siren 1952).

Shape

Elliptical to oval.

Size

Average length ranges from 58.1 to 60.6 mm (smallest egg 44.9 mm, largest 74.8 mm; Appendix 3). Average breadth ranges from 42.6 to 44.0 mm (smallest 33.9 mm, largest 48.9 mm; Appendix 3). In British Columbia, egg breadths differ significantly among females and are highly repeatable within females (repeatability = 0.95, F = 21.3, df = 10, 65, P = 0.0001; JME). Egg lengths also differ among females but to a lesser extent (repeatability = 0.49, F = 1.95, df = 10, 65, P = 0.058; JME).

Mass

Average fresh egg mass ranges from 61.2 to 66.6 g for estimates based on sufficient sample size (smallest 48.0 g, largest 80.5 g; Appendix 3). Egg mass is highly repeatable among females in British Columbia (repeatability = 0.95, F = 19.29, df = 10, 65, P = 0.0001; JME).

In British Columbia, eggs lose approximately 0.17 g/d incubation (8–10% of fresh egg mass); thus egg mass is predicted by number of days before hatching (Egg Mass = 55.3 + 0.17 x Days to Hatch; r²= 0.14, n = 737, P <0.0001; JME). In Minnesota, eggs lose 15.4% of mass during incubation; loss of egg mass varies with nest location, quality of the nest site, and year (M. C. Zicus unpubl. data). Total clutch mass averages 83.8% of female’s body mass (SE 9.7, range 60.2–109.9, 11 nonparasitized clutches, female mass measured at end of incubation; JME).

Females with previous breeding experience may lay heavier eggs (Mallory et al. 1994).

Color

Greenish (bluish green to olive-green). Color varies among females; large variation within clutches may be due to intraspecific brood parasitism.

Surface Texture

Smooth, slightly glossy.

Eggshell Thickness

Described as thin (Bent 1925, Bellrose 1980). Mean eggshell thickness of 197 eggs from 20 clutches was 0.393 mm (range 0.328–0.439; WFVZ); from 93 eggs (with membranes) from 32 broods in n. Ontario, 0.368 mm (SE 0.004, range 0.30–0.44; HGL), identical to eggshell thickness values for 52 eggs collected in 1981 from n. Minnesota (Zicus et al. 1988). Reported higher (mean 0.435 mm, SE 0.006, 19 eggs) at turn of eighteenth-nineteenth centuries (in Zicus et al. 1988).

Egg Components

Percentage dry weight of major egg components: shell: 28.0% (SE 0.40, range 22.2–33.8, 28 eggs from separate clutches); yolk: 57.3% (0.60, 51.5–70.0); albumin: 14.7% (0.50, 5.5–18.0) (J. M. Eadie and C. Nasello unpubl. data). Proportion of yolk and albumin increases significantly with egg mass, whereas proportion of eggshell does not (J. M. Eadie and C. Nasello unpubl. data). Larger eggs have proportionally more yolk.

Egg-Laying

Slow rate, similar to other Bucephala, Mergus, and Lophodytes . Laying begins with nest construction. Usually 1 egg every other day. Intervals between eggs in British Columbia: 1.87 d (SE 0.10, range 1–3 d for nonparasitized nests, 1–11 d in parasitized nests, 56 nests; JME). In n. Ontario, laying rates averaged 45.4 h/egg (SE 1.4, 31 clutches, 89 eggs; HGL), whereas in New Brunswick, laying intervals were 1.92 d (3 nests; Prince 1965) and in Minnesota 1.36 d (13 nests; Johnson 1967). Average duration of entire laying period in British Columbia: 14.7 d (SE 0.4, range 7–26, 73 nests; JME).

Most egg are laid in morning (0500–0700 h) and late afternoon (1700–2100 h). Time on nest during egg-laying ranges from 7 to 223 min (mean 64.0 min, SE 19, 12 females; JME). Longer times are typical of females close to clutch completion and beginning of incubation. During egg-laying, females may visit their nests 2–3 times during the day without laying (females only visit their nest once per day in Minnesota; Zicus et al. 1995); the function of this behavior is unknown, although it may play a role in guarding nests from parasitic conspecifics. Mean duration of all nest visits in British Columbia was 89 min (SE 18, range 1–339, 31 females; JME). Laying times in n. Ontario averaged 185 min (range 30–475, 37 observations; HGL) and increased with each successive egg (HGL).

M. C. Zicus (unpubl. data) found that female Common Goldeneyes in Minnesota did not change mass with any consistent pattern during egg-laying, suggesting that these females rely heavily on exogenous food sources for nutrients during egg-laying.

Intraspecific brood parasitism (egg dumping) occurs frequently (see Breeding: brood parasitism).

Onset Of Incubation And Broodiness In Relation To Laying

Females spent 0.5–78.5% of the day on the nest during laying; time on nest (particularly overnight attendance) increased near clutch completion (Zicus et al. 1995).

Incubation Patch

Single brood patch, on female only.

Incubation Period

Only females incubate. Incubation period (excluding 1 d for brooding in nest) varies from 28 to 32 d in most areas (Bellrose 1980, Mallory and Weatherhead 1993a). In ne. Ontario, incubation period averages 31.2 d (SE 2.8, 28 clutches; HGL); in central British Columbia, 29.1 d (SE 0.3, range 27–33, 57 clutches; JME); in n. Minnesota, ranges 28–30 d (12 clutches; Zicus et al. 1995). In Minnesota, female that spent more time off the nest each day had longer incubation periods (Zicus et al. 1995).

Parental Behavior

Males abandon nesting females after 1–2 wk of incubation (MLM). Females do not settle into a consistent incubation rhythm until day 5 of incubation, and break their consistency around day 29 when sounds from chicks in eggs may influence behavior (Mallory and Weatherhead 1993a). Females incubate continuously through night but take several recesses during day. Number of daily recesses varies (range 1–7, Siren 1952, Zicus et al. 1995; mean 2.7 (SE 0.1), Mallory and Weatherhead 1993a), as does average recess duration (mean range 40.8–138.7 min, Zicus et al. 1995; mean 114 min (SE 5), Mallory and Weatherhead 1993a). Reported incubation constancy varies considerably between studies (range 75–89%, Siren 1952, Semenov-Tyan-Shanskii and Bragin 1969; 36.7–96.3%, Zicus et al. 1995), averaging 81.2% (SE 0.4) for 16 females in Ontario (Mallory and Weatherhead 1993a). Early in incubation, females tend to take few but long recesses from nest, resulting in low incubation constancy (Mallory and Weatherhead 1993a, Zicus et al. 1995). Once a consistent rhythm is established, females maintain relatively similar numbers of daily trips from nest, but they increase duration of each trip, resulting in an overall increase in amount of time off nest as incubation proceeds (Mallory and Weatherhead 1993a, Zicus et al. 1995). During morning and afternoon incubation session, females adjust their position on nest approximately every 17–20 min, whereas they adjust positions every 33 min during overnight sessions (MLM). Patterns of incubation rhythms can differ substantially for females nesting on different lakes, and even between years for the same female (Zicus et al. 1995). Females usually take their first recess within 4 h of sunrise, and are often absent from nest between 1000 and 1600 h (Mallory and Weatherhead 1993a, Zicus et al. 1995). During incubation recesses, females usually forage out of sight of nest (MLM).

Females may be caught on nest; usually docile when handled (MLM). Nest defense increases through incubation, with females performing Broken-wing Distraction Display when flushed during last 6 d of incubation or on hatch day (Mallory and Weatherhead 1993b). If flushed early in incubation, females may desert clutch (probably varies with degree of conditioning to people and with severity of disturbance); females that desert or lose a clutch rarely renest (Zicus 1990). When flushed, females may defecate on eggs.

During incubation, females lose body mass. Estimates of amount of mass lost vary: 16.7–17.8% for females nesting near Sudbury, Ontario (Mallory and Weatherhead 1993a); 11.0–11.3% for females nesting in Minnesota (M. C. Zicus unpubl. data).

Hardiness Of Eggs

Minimum daily temperatures during egg-laying often drop below 0°C, and eggs may freeze; ducklings may still hatch from eggs cracked by freezing (Lumsden and Wenting 1976). Eggs may also withstand up to 1 d absence during incubation and still hatch (MLM).

Preliminary Events And Vocalizations

Tapping and peep calls can be heard up to 3 d before hatching.

Shell-Breaking And Emergence

The first crack (“star-pip”) occurs 24–48 h before hatching. Eggs hatch synchronously, usually within 12 h, often overnight or in early morning. Young vocalize occasionally during hatching; females may respond with a soft guttural chuckle (JME). Hens are highly attentive to nests during hatching and will remain on or close to nest if approached (JME, MLM). Nonetheless, hens still maintain a rhythm of departures from nest similar to that during incubation, although the amount of time away is reduced (Zicus et al. 1995). Pipped eggs or ducklings can be removed from under some females while they remain on nest (JME, MLM). This is typical of older, experienced birds that have been handled and banded in the previous year.

Parental Assistance And Disposal Of Eggshells

Eggshells and membranes may be removed after hatching but often remain (JME, MLM). Females, including prospecting hens, have been observed to eat eggshell fragments and membranes (JME, M. C. Zicus pers. comm.). In British Columbia, no reliable correspondence between number of eggs hatched and number of shell membranes left in nest (JME); hence, this method of determining clutch size is not reliable for Common Goldeneyes (JME, MLM).

Condition At Hatching

Precocial. Covered with down at hatching, eyes open. Black head with large white cheek patch extending under chin. Back and sides black with white patches on rear edge of wing, side, and rump. Underparts white. Legs and bill gray, iris brown. Mass 38.1 g (SE 0.4), culmen length 12.8 mm (0.09), culmen width 8.3 mm (0.05), tarsus length 25.3 mm (0.15 mm) (93 ducklings; JME).

Departure From The Nest

Young remain in nest 24–36 h after hatching. Plumage dries within 12 h. At nest departure, female flies repeatedly to nest hole, eventually sitting below cavity and calling. Young jump from nest in rapid succession (40–150 s, 5 broods; Johnsgard 1978) and follow female to brood territory (lake, river, pond) which may be several kilometers away (Wayland and McNicol 1994).

Growth And Development

Growth constants (K) estimated by logistic regression of weight on age for ducklings captured between 21 and 57 d averaged 0.09 (SE 0.015, males) and 0.08 (0.024, females). These constants did not differ from those of congeneric Barrow’s Goldeneyes. Young thermoregulate soon after hatching; females brood young occasionally for first few weeks. Newly hatched (1 d old) Common Goldeneye ducklings can maintain body temperatures during exposure to cold temperatures (Koskimies and Lahti 1964). After leaving nest, ducklings swim and feed with ease. Most feeding in first few days is by surface dabbling, but ducklings can dive within 1–2 d after leaving nest. Dives increase in duration and efficiency after the first week.

Development of Juvenal contour feathers is similar to that in Buffleheads (Gauthier 1993). Feathers appear first on flanks and scapulars and then on tail after approximately 20–22 d. Wing feathers begin to unsheathe after 3 wk (23–25 d), and belly feathers appear after 1 mo. Head, back, and neck feathers emerge last. Juvenal plumage is complete by around 50–55 d.

Brood Survival

In British Columbia, survival of young is variable, averaging 36.5% (SE 3.8, range 0–100%, 86 broods, 1984–1992; JME). Average brood size decreased from 8.7 (SE 0.2) at hatching to 3.1 (0.4) near fledging (86 broods; includes only nests where ≥ 1 young hatched and left nest; JME). Many females, however, lost their entire brood (33.7% total brood loss), and the modal number of young fledged was 0. Brood survival elsewhere also appears to be low: Maine 28.5% (Gibbs 1962); New Brunswick 53% (Cartar 1958), n. Ontario 31–53% (Wayland and McNicol 1994). Brood survival may be highly dependent on brood habitat characteristics, principally the availability of aquatic invertebrate food resources but also weather and predation (Eriksson 1978, Wayland and McNicol 1994; see Breeding: brood site).

Mortality is highest during the first week of life (Savard et al. 1991); little mortality occurs after 21 d. Primary causes of death are rain and cold weather shortly after hatching, predation by avian and mammalian predators and northern pike, and infanticide by Common Goldeneye females, Red-necked Grebes (Podilymbus podiceps), and Common Loons (Gavia immer).

Brooding.

Broods are attended by female only (Fig. 5). Young are highly independent, requiring little direct care (Pöysä 1992). Females defend brood territories, presumably ensuring high-quality food resources and preventing attacks by conspecifics or predators. Females brood young at night or during inclement weather, particularly in first 2 wk after hatching; they brood most often on loafing platforms, floating logs, or fallen timber near shore. Brood cohesion is strong in first 2–3 wk, and young respond quickly to female alarm calls, usually by swimming rapidly after female, occasionally by diving or scattering if brood is directly attacked or threatened. This scattering behavior is commonly observed following a low-level helicopter survey of a lake for broods (MLM).

Parental Carrying Of Young

Early reports suggested that females carry young from nest site on their backs (see Bent 1925), but this has never been confirmed and seems unlikely. After leaving nest, ducklings occasionally scramble up on a female’s back while swimming, but carrying of young is infrequent and not initiated by parent.

Brood Site

Females often move broods from nesting lake to a rearing lake (e.g., Grinnell 1901), although this appears to depend on lake size and productivity. An abundant supply of aquatic invertebrates is a key factor in selection of the rearing lake (Eriksson 1978, Eadie and Keast 1982, McNicol and Wayland 1992, Wayland and McNicol 1994); clustered lakes also appear to be preferred for rearing (Wayland and McNicol 1994). Distances between nesting and rearing lakes may be up to 10 km, but the distance traveled does not appear to influence duckling survival (Wayland and McNicol 1994).

Intraspecific Brood Parasitism

Also called egg-dumping or nest parasitism. Occurs frequently in both North American and European populations, particularly where nest boxes are available (Eriksson and Andersson 1982, Eadie 1991). Frequency is difficult to determine since eggs of conspecifics are similar; different criteria may provide variable estimates (Eriksson and Andersson 1982). In Sweden, frequency ranges from 23 to 41% (Eriksson and Andersson 1982, Dow and Fredga 1984).

Based on multiple criteria of egg morphology, clutch size, laying intervals, and DNA fingerprinting, frequency of intraspecific brood parasitism (IBP) in British Columbia ranges from 37.5 to 54.0% of nests among years (1984–1992) and from 0 to 77.8% among lakes. Rate of parasitism is significantly correlated with the degree of nest limitation and is highest in nests initiated early in breeding season (Eadie 1989, Eadie and Fryxell 1992). Clutch sizes in parasitized nests can be as large as 24 eggs, but > 60% of parasitized nests in British Columbia contained < 13 eggs (JME).

Average nest and hatching success of parasitized nests in British Columbia do not differ from those of nonparasitized nests. Nest success (percentage of nests where at least 1 egg hatched) is only reduced when total clutch sizes exceed 16–20 eggs. In British Columbia (JME), average number of parasitic eggs in parasitized nests is 3.6 (SE 0.4, range 1–11, 75 nests); hatching success (proportion of eggs that hatch in successful nests) is significantly lower for parasitic eggs (83.1%) than for host eggs (90.7%) because some parasitic eggs are laid after incubation starts. Host females do not defend their nest against parasites; antiparasite defenses consist primarily of nest desertion when clutch sizes are large. Posthatching brood survival does not differ significantly in parasitized and nonparasitized broods once the effects of hatch date and female age are controlled (Eadie 1989).

Interspecific Brood Parasitism

Also frequent. Reported for both natural cavities and artificial nest sites. In the early 1900s, Brewster (in Bent 1925) reported clutches mixed with those of Hooded Mergansers in natural cavities. Mixed clutches also reported with Barrow’s Goldeneye, Common Merganser, Bufflehead, Wood Duck (Aix sponsa), and Smew (Grenquist 1963, Eadie et al. 1988, Zicus and Hennes 1988). In Minnesota, Common Goldeneyes were involved in 64% of 206 multiple-species nests found in nest boxes (Zicus and Hennes 1988); 30 of 374 of nests (8%) used by Common Goldeneyes also contained either Wood Duck or Hooded Merganser eggs (M. C. Zicus pers. comm.). Common Goldeneyes in British Columbia frequently lay in nests of Barrow’s Goldeneyes, and vice versa, apparently indiscriminately (Eadie 1989). Mixed clutches with Buffleheads also occur, but less commonly; these nests are usually incubated by a Common Goldeneye hen (Gauthier 1993). Common Goldeneye nests are used by other secondary cavity-nesting species such as Starlings (Sturnus vulgaris) and Tree Swallows (Tachycineta bicolor), but this is the result of competition for the nest site rather than brood parasitism per se.

Eggs have hatched successfully when laid parasitically in all of the waterfowl species mentioned above, although quantitative studies are lacking. Bouvier (1974) reported that 14 of 17 Common Goldeneye eggs hatched when laid in nests of Hooded Mergansers; conversely, 4 of 5 Hooded Merganser eggs hatched when laid in Common Goldeneye nests. Patterns of parasitism between Common and Barrow’s goldeneyes in British Columbia are virtually identical to those described for intraspecific parasitism above. Eadie and Lumsden (1985) reported that survival of Common Goldeneye ducklings was higher in broods parasitized by Hooded Mergansers than in nonparasitized broods; Common Goldeneye hosts might benefit when parasitized interspecifically through a reduction of predation risk on host young. Subsequent experimental studies have not corroborated this result (Eadie 1989).

Broods frequently amalgamate after leaving nest (also called creching, brood-mixing, or gang-brooding; Phillips 1925, Bellrose 1980, Eadie et al. 1988). In British Columbia, 35% of Common Goldeneye broods were involved in brood mergers (40 broods, 1984–1986; JME). Brood amalgamation appears to occur in 2 circumstances. (1) Some females abandon their broods soon after hatching and their ducklings then merge with other broods. Cartar (1958) reported that up to 14% of all young sighted in New Brunswick were without a parent in attendance. Experiments in British Columbia demonstrated that females with experimentally reduced broods were more likely to abandon their young, as were females that experienced high duckling mortality in the first week (J. M. Eadie and B. Lyon unpubl. data, Pöysä 1992). Abandoned young often, but not always, joined another brood. (2) Some females “lose” ducklings after a territorial dispute with another female. Young scatter and mix when females become involved in fights; when the dispute ends and broods reconverge, some or all of the young may be transferred to 1 brood (most often the brood of the territory owner). Females that lose young in such a manner tend to be those that hatched broods late in a season.

The functional significance of brood amalgamation is uncertain. Savard (1987) and Gauthier (1993) argued that brood amalgamation in Barrow’s Goldeneyes and Buffleheads, respectively, occurred simply as an inadvertent consequence of territorial disputes. Others (reviewed in Eadie et al. 1988) suggest that brood amalgamation may function as an antipredator adaptation or as a mechanism of adaptive brood desertion and adoption. Too few quantitative studies on marked individuals have been completed to assess these possibilities.

Females abandon young before young can fly, usually at 5–6 wk of age, but occasionally as early as 1 wk of age (see above). Young are able to fly at 56–65 d (Johnsgard 1978, Bellrose 1980).

Poorly known. Mortality of immatures is high; immatures experienced the highest mortality of any duck banded in Minnesota (Moyle et al. 1964). Johnson (1967) estimated mortality of first-year birds to be 36% due to of hunting; losses of adults to hunting were considerably lower, suggesting that immature birds may be most susceptible to hunting pressure near their natal area. Annual mortality rate for 258 birds banded as flightless young in Minnesota was 82% (Moyle et al. 1964), although more recent estimates are lower (M. C. Zicus pers. comm.). Similarly, data from hunter-shot birds (1976–1991) in e. Canada and ne. U. S. suggests that, over this region, only 13% of the kill of Common Goldeneyes took place early in hunting season (Sep) and that as much as 57% took place in Nov and Dec, suggesting that most of the birds shot were not necessarily local immatures (preliminary analysis, H. Boyd pers. comm.). Thus, survival of local immature birds may be higher in areas where hunting pressure is lower, and survival undoubtedly varies regionally.