Breeding

Pair Formation

At start of breeding season in Mar, Apr (depending on latitude), either on male’s territory or loafing areas (Tinbergen 1960). In areas covered by ice, delay nest-building and egg-laying but not territory establishment (Morris and Chardine 1985). Males regurgitate food for females for egg formation, replenishing reserves. Late arrivals pair after onset of breeding of early-nesting pairs and attempt to establish territories among established pairs (Burger 1984).

Nest-Building

Male and female choose site and make scrape lined with vegetation, feathers, etc. Nest cup shaped by birds with breast and feet (Tinbergen 1960). Material added throughout incubation (Bent 1921).

First/Only Brood Per Season

Figure. 8 . One brood/yr. May lay replacement clutch if first destroyed. Can lay up to 12 eggs if first egg removed before second laid (Pierotti 1979, 1982). Most clutches initiated early through mid-May, can be initiated in late Jun (Pierotti 1982); birds need 4–6 d to lay 3-egg clutch. Incubation begins with second egg, lasts 30–32 d (Drent 1970). Chicks fledge 6–7 wk after hatching, are fed on natal territory until 12–15 wk old (Burger 1984). Parents and chicks abandon territory in early fall. Chicks cared for off territory for up to 6 mo (Drury and Smith 1968, Burger 1984).

Selection Process

Male and female dig various scrapes, fill them with vegetation; up to 3–4/territory. Both Choke over specific scrapes each has built; if Choke together, site chosen. Ultimate choice is where female lays eggs (Hand 1985).

Microhabitat/Site Characteristics

Site protected from prevailing wind(s), placed next to large object (log, bush, rock), which acts as visual barrier between nest and closest neighbors (Pierotti 1982, Burger 1984). Nests in rocky areas located in crevices, in depression scraped in sand or soft soil, or pressed down into short vegetation. Located above high tide, splash zone on beaches, marine terraces.

Construction Process

See above, Nest Site: selection process. Built by pair during daylight several days prior to egg-laying. Vegetation added throughout incubation.

Structure And Composition Matter

Bowl scraped into substrate, lined with vegetation, feathers, plastic, rope, etc. Some nests, especially in sand, have little or no lining (RJP).

Dimensions

Inner cavity averages 15 cm, range 10–20 cm; outer diameter averages 30 cm, range 25–35 cm; depth 5–7 cm (Bent 1921, Cezilly and Quenette 1988).

Microclimate

Protected from prevailing wind. If shelter next to nest removed, nest material blows away (Pierotti 1979, 1982). Shelter lowers windspeed above nest cup, reduces wind chill for incubating adult or uncovered eggs (Pierotti 1979).

Maintenance And Reuse Of Nests, Alternate Nests

Adults add to nest throughout incubation. Nest not reused, but specific site often reused from year to year. Alternate nests built, not used (Pierotti 1979).

Nonbreeding Nests

Alternate nests (indistinguishable from used nests) sometimes built on territory before final nest site chosen. Only final nest (where eggs are laid) is used. Counts of nesting pairs should be conducted during late incubation, otherwise numbers may be overestimated because of counting nonbreeding (alternate) nests.

Shape

Variable; most ovoid.

Size

See Appendix 1 . Typically 65–75 mm long, 45–55 mm wide (greatest breadth).

Mass

85–105 g (10–12% of adult female mass; Pierotti 1982). Second egg sometimes heaviest, third egg smallest, although difference reduced in well-nourished females (Drent 1970, Pierotti 1982).

Color And Texture

Smooth, nonglossy, with finely granular surface. Usually light olive, buff, or greenish, may vary from pale whitish buff to deep brownish buff. Speckled, spotted, blotched black, dark brown, or dark olive. Terminal egg (usually third) typically scrawled or streaked, especially on wide end (Harrison 1978).

Egg-Laying

Nest essentially complete prior to laying first egg. Eggs usually laid in early morning at roughly 2-d intervals (Drent 1970). Male feeds female throughout laying; female rarely leaves territory during laying. Male often absent obtaining food for female, reducing mate-guarding opportunities. Females strongly resist all forced copulation attempts, reducing need for mate-guarding (but see Morris and Bidochka 1983). If first egg lost, females relay for up to 24 d, depending on physiological condition (Pierotti 1979, 1982). If clutch lost, females require 7- to 10-d refractory period to produce new clutch. Replacement clutches often have smaller or fewer eggs than first clutch (Pierotti 1979). Intraspecific nest parasitism and dumping not observed. Chick adoption common (5–10% of pairs), resulting in chick-generated nest parasitism (Pierotti and Murphy 1987, Pierotti 1991).

For detailed account of egg temperature and shift between adult and chick in contribution to egg temperature, see Drent 1970 .

Onset Of Broodiness And Incubation In Relation To Laying

Incubation begins with laying of first egg. Effective incubation begins with laying of second egg; brood patches not fully vascularized, depilated until then (Drent 1970).

Incubation Patches

Three incubation patches, 1 on either side of keel, 3 posterior to these. Present in both sexes. Patches larger in female (Drent 1970, RJP).

Incubation Period

First egg laid day 0, hatches day 30. Second egg laid day 2, hatches day 30. Third egg laid day 4–5, hatches day 31–32 (Drent 1970, Pierotti 1979, 1982). Delayed hatch in third egg, combined with lighter weight of chick, generates “third chick disadvantage,” whereby third chick obtains less food, grows more slowly than first- and second-hatched chicks (Pierotti 1982). Can lead to differential mortality (Parsons 1975).

Parental Behavior

Incubation shared equally by male and female, especially in successful pairs (Burger 1984, Morris 1987). During good feeding conditions, female spends more time on nest than male does; female also incubates at night (Pierotti 1979, 1987a). Male incubates mostly when female absent, will remain on nest when female returns (Pierotti 1979). Shifts last 3–4 h. Eggs covered about 75% of time until clutch complete, about 98% of time after completion (Drent 1970). Typical change-over occurs when mate returns, pair exchange Long Calls, returning mate approaches nest, may Mew-call or Head-toss. Incubating bird either gets off nest or Chokes, indicating tendency to remain. If incubating bird gets off, arriving bird walks on to nest cup, lowers breast into cup, paddles feet to adjust eggs and feathers. Once settled, preens, adjusts eggs with beak, settles to rest or sleep. If bird on nest Chokes and remains, mate may pick up nesting material, return Mew-calling. If this induces partner to leave nest, bird settles on nest as above, placing nesting material around nest.

Hardiness Of Eggs

Eggs can be left unattended for several hours without affecting hatchability (Drent 1970, Burger 1984). All eggs lost to predation lost during periods of inattention (Drent 1970, Morris 1987, Pierotti 1987a). Eggs left unattended for extended periods show hatching delay (Drent 1970).

Preliminary Events And Vocalizations

Five to 6 d prior to hatching, fine webwork of cracks appear at 1 point on shell adjacent to widest egg circumference. After 1–2 d, small “pipping” hole appears in spot, through which tip of chick’s beak with egg tooth is visible. Once hole exists, chick produces peeping sounds. Adults respond with Mew Calls. Adults switch own diet to fish when chicks emit first calls within egg (Pierotti and Annett 1987, 1990).

Shell-Breaking And Emergence

Chicks hatch before midday. First and second chick within 3–4, third chick up to 24 h later. Each egg takes about 2 d from appearance of pipping hole to chick emergence. Shell breaks just above greatest diameter; chicks push out using feet (RJP).

Parental Assistance And Disposal Of Eggshells

Parents give no physical assistance, watch over hatching chicks and Mew-call at intervals. Some adults remove shells from nest, others allow shell to be crushed into nest lining (Tinbergen 1960, RJP). Experiments indicate reduced predation by crows if eggshells removed after hatching (Tinbergen 1960), but only on nests unattended by parents. At attended nests, adults cover eggs and hatching chicks throughout hatching process, rendering adaptive function of eggshell removal somewhat problematic (RJP).

Condition At Hatching

Chicks nidifugous, semiprecocial with open eyes, thick gray down marked with black spots over entire body, weigh 60–75 g. Beak black, except pinkish egg tooth (retained 2–3 d), legs black to dark gray (Bent 1921, Dwight 1925; see Fig. 9). Remain in nest for several hours while drying. First 2–3 d move about nest vicinity; at 1 wk can run about freely, remain on natal territory. Live off yolk reserves first few days, fed by parents within hours of hatching.

Growth And Development

On day of hatching: first- and second- hatched chicks weigh 60–75 g (third-hatched chicks slightly smaller); day 5: 100–150 g; day 10: 150–300 g (Fig. 9); day 15: 300–600 g; day 20: 400–800 g; day 25: 500–900 g; day 30: 650–1,100 g (Pierotti 1979, 1982). Chicks weighing < 200 g on day 15 or < 600 g on day 30 unlikely to survive (Pierotti 1979).

Flight feathers emerge between day 15 and 20; primaries and accompanying coverts emerge first, followed by coverts on back and belly; rectrices emerge day 25–30. All feathers fully emerged by fledging, day 40–50. Tarsus about 30 mm long at hatching, grows steadily to asymptote of 60–70 mm at day 30–35. Culmen about 18–20 mm at hatching, grows steadily to asymptote of 30–35 mm at fledging (about day 50) (Elkowe and Payne 1979, Pierotti 1979).

Young chicks brooded on cold or rainy days until 7–10 d old. Chicks maintain homeothermy within 24 h of hatching, expend about 7% total metabolic costs thermoregulating (Dunn 1976). Chicks ambulatory within 24 h, actively move about by 3–5 d, start stretching wings at 15 d, beating wings about 30 d, jump up and down beating wings between 30 and 40 d, first become airborne about 40–45 d, capable of actual flight by 45–50 d (Pierotti 1979). Chicks have Begging Calls (see Vocal array) at hatching; postural and vocalization changes described above. Chicks peck at, pick up objects, huddle together to sleep or rest. When parent(s) return with food, chicks rush parent and beg actively. If parent regurgitates, chicks scramble to grab food, often pulling fish from parent’s mouth. Competition appears to be “scramble”; no obvious aggression among siblings. Larger (earlier-hatched) chicks usually win scrambles. If food provided not adequate for 3 chicks, smallest (youngest) chick may wander off and be attacked or killed (60–70%) or adopted (30–40%) by neighboring adults (Graves and Whiten 1980, Pierotti 1980, 1991, Holley 1984, Pierotti and Murphy 1987).

Brooding

Both parents brood young, female more in total (Pierotti 1979, 1982). Brooding behavior begins with hatching of first egg and continues until chicks 7–10 d old. Chicks > 5 d brooded only during inclement weather. One adult always present and attending chicks until > 30 d in successful pairs (Burger 1984, Morris 1987).

Feeding

Both parents feed chicks from day of hatching until 11–12 wk. Males feed more often before fledging (0–50 d), females more often after fledging (50–80 d) (Burger 1984, Pierotti 1987a). Adults leave territory to forage, return with food in proventriculus. On return, chicks either rush up and beg, or adult Mew-calls, attracting chicks. Young chicks (<10 d) peck at red spot near gonys, may stimulate regurgitation by adult (Tinbergen 1960), but many adults regurgitate before chicks peck. Major function of red spot may be to orient chick–feeding during early behavioral development. Older chicks (>10 d) do not peck at red spot, but give Begging Call while oriented at base of adult’s mouth (RJP). Adult regurgitates food, holds bolus in bill for young chicks (<10 d), regurgitates bolus onto ground for larger chicks. Chicks pick up pieces or entire prey items, swallow whole.

Young chicks (<10 d) fed small prey items (small fishes, euphausiids, copepods, insects, earthworms) or well-digested prey that breaks into pieces small enough to be handled (e.g., fish). Small chicks cannot handle entire large fish or invertebrates (mussels, crabs, squid, urchins) or human refuse. Adults feeding large food items to offspring lose them to death or adoption (Pierotti and Annett 1987, 1990, 1991). Large chicks (>10 d) can handle larger food, swallow entire fish, squid, or refuse. In Newfoundland, chicks fed capelin until 2–3 wk old, squid when chicks > 2 wk old. Chicks fed refuse grow more slowly, survive poorly compared to chicks fed natural diets (Pierotti and Annett 1987, 1990, 1991). In Holland, increase in garbage and invertebrates fed to chicks associated with decrease in breeding success (Noordhuis and Spaans 1992). Chicks fed every 3–4 h by male, every 4 h by female prior to fledging (Pierotti 1987a, Pierotti and Annett 1991). Males fed chicks 160 g capelin or 180 g squid/meal, females 120 g capelin or 100 g squid/meal (Pierotti 1987a, Pierotti and Annett 1987). In Massachusetts and Maine, adults feed chicks small fish, insects, marine invertebrates (RJP). Feeding refuse to small chicks may be cause of low fledging success in some New England colonies (< 1.0 chick/nest in Massachusetts, compared with nearly 2 chick/nest in Newfoundland) (see Kadlec and Drury 1968, Hunt 1972, Pierotti 1982, Pierotti and Annett 1991). Chicks try, but unable to ingest large pieces of refuse, intact mussels, or crabs as food in both Newfoundland and Massachusetts (RJP).

Nest Sanitation

Chicks (and adults) defecate on territory but away from nest. Adults also defecate while flying. No parasites observed in nest, but young can become infested with fleas if mammals (rats, rabbits) present on nesting islands.

Parental Carrying

Does not occur.

A few triads (1 male, 2 females) observed, all of which incubate, brood, and feed offspring (Shugart 1980). These groups typically unsuccessful in fledging offspring.

No nest parasitism (eggs) observed. Chicks often adopted when they wander into territories of neighboring pairs (Graves and Whiten 1980, Pierotti 1980, 1991, Holley 1984, Pierotti and Murphy 1987).

Departure From Nest

Chicks leave nest within 24 h, remain on nesting territory and around nest 40-plus d. Leave nesting territory initially with first flight at 45–50 d. Chicks fully grown, fully feathered, and at or above adult mass at fledging (Pierotti 1979). Return to nesting territory to rest and be fed up to 12–15 wk of age (Burger 1984).

Growth

Most growth occurs prior to fledging. Mass probably lost while juveniles learn to forage for themselves. Wings and tail may continue to grow after fledging.

Association With Parents Or Other Young

Some chicks associate with adults, beg food up to 6 mo postfledging (Drury and Smith 1968, RJP). Newly fledged chicks gather in groups around colony, also concentrate on areas where food predictably obtained, e.g., rocky intertidal, fishing activities, refuse dumps. Large numbers of juveniles associate with feeding humpback whales in Gulf of Maine, off s. Nova Scotia, in fall and winter; feed on fish driven to surface by foraging whales (Pierotti 1988).