Common Murre Uria aalge Scientific name definitions
Version: 2.0 — Published August 6, 2021
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See Behavior: Agonistic Behavior, and Colony Attendance below. Ledges occupied en masse after several days of rafting below breeding cliffs. Process of pair formation not well known; may occur in rafts below cliffs (38) and/or in clubs (218), but re-pairing after divorce suggests that behavioral interactions with colony neighbors prior to egg laying are involved in the formation of new pairs (311).
Colony Attendance Prior to Egg-Laying
At low latitude, e.g., Farallon Islands, California (38°N, 122°W; midsummer daylight 05:30–20:30), numbers attending cliffs highest during midmorning (09:00–12:00), lowest during late afternoon and evening; during prelaying may be present only during midmorning (Farallon Islands; 27). Similar pattern at Isle of May, Scotland (56°N; 92), and also at Witless Bay, Newfoundland (AES). At high latitude (e.g., Cape Thompson, Alaska; 68°N, 166°W; midsummer daylight continuous), daily pattern completely opposite: buildup of numbers in afternoon and evening and decrease during morning (16). Pattern perhaps related to feeding: at Farallon Islands, most intense feeding at dawn and late afternoon (27); at Cape Thompson, most intense feeding in morning (darkest hours; 16; see also 355).
In northern colonies (e.g., Cape Thompson; 68°N; not much or no daylight October–March): first birds arrive early May, 2 months before laying (at this time, ocean mostly ice covered); last adults depart late September with departure of chicks (16; see Figure 1). At Semidi Islands, Alaska (56°N), initial occupation of ledges first week April, about 57 d before first egg; last adult and chick gone by end of August (355, 356).
In southern populations (e.g., Farallon Islands, 38°N), during years when food availability high or “normal” (27; see also 357, 358), breeders return to cliffs in October, 6 months before laying; last birds depart first week of August. When food not available and/or winters especially stormy (El Niño), arrival delayed until spring, 1 month before laying. Similar pattern at Isle of May, Scotland (92).
In eastern Canada, appears near colonies during March and early April, at southern locations (e.g., Gulf of St. Lawrence and Newfoundland [46–50°N], 4 weeks later in Labrador [53–56°N]); earlier at small colonies in Bay of Fundy (44°N; 359; DNN). In Newfoundland, numbers stable 1 June (first egg about then) to late July (first fledge early July); then decline to zero by mid-August (360).
In colonies in the northeast Atlantic, arrival dates varied between 28 January and 18 April. The timing of arrival was not related to latitude, but the pre-laying period was explained by colony size, being longer in large colonies (361).
Initial visits sporadic day to day, mainly during morning, absent at night, and not when weather stormy; present for a few days, then absent for a few days to weeks in most years (290, 319, 27, 362, 92). Visitation persistent and overnight shortly prior to egg-laying, especially in morning. Incubation through hatching, therefore, is best period for determining population size (363, 355; see also 364). Peak numbers in the colony occur late incubation, when nonbreeders also present. When chicks depart, numbers of adult-plumaged birds drop rapidly owing to high breeding synchrony.
Many factors affect day-to-day attendance. During prelaying at Farallon Islands, adults disappear during storms and when barometer depresses, even if no storm directly passes (27; see also 365); at other locations, correlations with wind speed and tide (289, 366). During breeding, at some locations presence not correlated with wind speed, direction, temperature, pressure, cloud cover, precipitation, or tide (360, 355); at others, inverse relationship with wind speed (363), or direct correlation with maximum air temperature (34). Relatively high proportion of nonincubating (or brooding) mates on cliffs indicates good feeding conditions (235, 367, AES; see also 368).
No nest built. Prospecting pairs sometimes drop pebbles at site where egg may be laid.
Egg-laying highly synchronous: 70% of all eggs laid within 10 d, 90% within 15 d; SD for average date of laying at Farallon Islands only ± 3.6 d (369). Egg-laying normally skewed toward early part of egg-laying period (27, 356). Laying within subcolonies, and among neighbors, even more synchronous than in entire colony (370, 371).
Interannual variation extensive in date of laying (Figure 1). At Farallon Islands, central California, 1972–1983, in response to climate variation, especially El Niño-Southern Oscillation (ENSO), mean date ranged 31 d (9 May–9 June); the average date of laying, 1972–2003, was 18 May (± 3.6 d), with date related directly to intensity of spring upwelling and timing of drop in sea-surface temperature (27, 369). Similar pattern evident at Castle Rock, northern California, 2007–2017, with mean date ranging 25 d, 27 April–22 May (232). At Farallon Islands, laying became earlier as population grew (27). At Gannet Islands, Labrador, 1981–1983, median date range 9 d (15–24 June), related to time of sea-ice break up and associated conditions (29, 327, 171). At Great Island, Witless Bay, Newfoundland, 1983–1984, median date range 8 d (18–26 May; DNN). At Skomer Island, Wales, timing from early to late May is inversely related to the North Atlantic Oscillation during the previous winter as well as population size (372).
Individual variation in laying date, with some females laying consistently before, later than, or at same time as mean laying date of subcolony (370, 373). Late laying persists despite consequential lower breeding success (see Demography and Populations: Measures of Breeding Activity). Young murres, especially those breeding first time, lay later than the average (374).
U. a. inornata: Alaska: Cape Thompson (68°N; 1960), median 10 July (16); Bluff (65°N; 1987–1991), median 21 June (375); Cape Pierce (59°N; 1989), mean 29 June (376); St. Lawrence Island (62°N; 1987), median 29 June (34); Pribilof Islands (57°N; 1977–1989), mean 1 July (377); Semidi Islands (52°N; 1979–1981), mean 17 June (356); Barren Islands (59°N; 1993–1998), median hatch date minus mean incubation period (32 d), 1–15 July (378). Triangle Island, British Columbia (48°N; 2002–2007), mid-May but a 25 day range in median lay date across years, earlier in 2000s than in the 1980s (37).
U. a. californica: Farallon Islands (38°N; 1972–1983), mean 18 May, but average ranging 9 May to 9 June; mean generally earlier as population grew, ~15 May to 10 May (27). Castle Rock (42°N), mean laying also mid-May (232).
U. a. aalge: Gannet Islands (54°N; 1981–1983), median 15–24 June (29); Great Island (47°N; 1983–1984), median 18–26 May (DNN), but delayed to last week of May to first week in June in 1998–2003 (median lay date: 1998, 2001, 2002, 2003, 1 June; 1999 and 2000, 25 May, AES); Cape St. Mary's, Newfoundland (47°N; 1980–1984), average median hatching date minus mean incubation period, 18 May (379); Isle of May, Scotland (56.2°N; 1981–1985), median lay date ranged 5–9 May (17).
No second broods, but replacement eggs laid if first lost. At Farallon Islands, replacement laid 15.1 d (range 13–23, n = 50) after first is lost; few if any further replacements (27). Similar at Gannet Islands (1981–1983): 15.9 d (n = 59) from loss of first egg to replacement (29); 15.5 d at Gull Island (359).
Colony Attendance by Non-Breeders
More non-breeders present between peak hatching and fledging (see above; 360). Best/only data on this from marked individuals in Scotland, pertaining to U. a. aalge, and, therefore, likely most applicable to U. a. californica, which has a similar annual cycle (Figure 1). Immatures visit colony earlier and earlier in season and spend more time there as they grow older, but always arrive later than adult breeders. First-time breeders arrive earlier than non-breeders of same age class. No difference related to sex (see 155 for details). Non-breeders are present throughout chick rearing and they sometimes pair with widowed birds (311).
Fall visitation as follows, depending on year (percent composition): 51–67% breeders of previous breeding season, 0–42% non-breeders and site holders (breeders), 10% first-time breeders, and 0% immatures <5 yr. Females present slightly more and earlier than males. Some breeders never visit during fall (380, 381, 15). Proportion of sites visited at least once during fall and number of days visited highest for successful sites and lowest for sites where no egg laid previous season; densely populated portions of colonies visited most often. Fall occupation likely reinforces site ownership and pair bond (380, 382).
Colony departure is more synchronous than arrival, as late birds fail, then depart, and breeders prepare for annual molt (see Appearance: Molts).
No nest; site selection process involves both partners engaging in bowing and dropping small pebbles at potential sites; egg is laid in final bowing location (AES). Attracted to other breeding murres, as well as to decoys placed together on suitable habitat, accompanied by vocalizations, where murres have formerly bred within 40 km of existing colonies (e.g., 24, 383, 160). Individuals that establish new colonies tend to be slightly older than first-time breeders at established colonies; e.g., 5–6 yr of age compared to 3–7 yr at Isle of Canna, Scotland (154).
In small concentrations to avoid predators, especially in colonies exhibiting decline, favors clefts, crevices, and area under boulders (384; see also 308, 340, 341, 101). In (more usual) denser concentrations, favors narrow ledges or flats adjacent to cliff walls or large rocks, against which one line of adults lean (forward) while incubating. On Pribilof Islands, breeding ledges averaged 60 cm wide, sometimes as narrow as 10–20 cm, with no overhang; 3–9° slope, with a back wall sloping slightly away (385). More than one line of pairs can occur on wider ledges, with just the inner pair against the back wall (see 364: Fig. 3). At St. Lawrence Island, Alaska, equal numbers occupied level or sloping ledges, but higher proportion on flat terrain laid eggs; presence of neighbors also important (34). In Newfoundland, ledges generally wider and lower than those of Thick-billed Murre, where both bred together; Common Murre sites usually without a wall; <10% bred on narrow ledges, where breeding success is low (327, 192).
See Habitat. Usually in a small depression on broad to narrow rock ledges of steep cliffs, stacks, or gently sloping terrain on rocky headlands and low-lying islands; only rarely in crevice, caves, and under boulders; often uses a wall on one side of breeding site; avoids larger depressions where water collects.
Construction Process and Structure
No nest; egg laying sites on bare rock, less commonly on soil or guano; some pebbles or debris may be manipulated by adults and dropped nearby to eventually be cemented to ledge by guano (38, 386, 387).
A pair's breeding space occupied by 2 birds, standing side by side or front to back depending on position of neighbors. Mean density about 20 breeding pairs/m2 on broad, flat area, or about 500 cm2/pair (364, 387).
No data. Usually stable and dry bare rock ledge or platform (does not collect water); includes marine air flow around cliffs, often strong currents with salt spray during windy conditions or when ocean swells are large.
Maintenance or Reuse of Breeding Sites
No nests, therefore no maintenance needed. Individuals normally use same site year to year as judged among individuals color-banded (e.g., 308, 309) or having distinctive plumage, such as bridling (153); 99.3% (n = 741 banded) at Isle of Canna, Scotland, 1973–1982, bred in same subcolony as previous year (154). At Skomer Island, Wales, 1973–1975, 96% (n = 74; 308), and at Isle of May, Scotland, 1982–1993, 91% (n = 470; 156) returned to same breeding site. Only data known for North America: Great Island, Witless Bay, Newfoundland, 1995–2001, >95% (n = 72; 311).
Intertidal rocks in vicinity of colonies attended mostly by 2- and 3-yr-olds; some of the latter and all older nonbreeders attend “clubs,” usually above subcolonies. Vantage points allow subadults to view breeders' activities, perhaps learning appropriate behaviors as well as available breeding spots. As nonbreeders age, they visit fewer subcolonies; 64–69% in a given year visit ledges near natal subcolony (306, 155). Immature nonbreeders manipulate pebbles and vegetation, in a seeming vestigial ‘nest-building’ behavior, more so than adults; vegetated areas often denuded (386) by physical activity and accumulated excrement. No data from North America owing to lack of marked individuals.
Large relative to body size, representing 9–11.5% of adult body mass (388, 29); egg size to parental body size relationship consistent with other auks ~12% of adult body mass (192). Yolk large (34–38% of egg content), and forms rapidly compared to other seabirds (389, 390). Rate of yolk formation among first-laid eggs varies by year and individual: 12–18 d (391, 390). Yolks of second (replacement) eggs formed more quickly (average 9.3 d) than first eggs owing to more rapid yolk deposition (392). From an evolutionary standpoint, large eggs of murres result in large chicks with sufficient yolk at hatching to withstand short-term food shortage, perhaps related to sea-ice cover (393). For egg composition, see Birkhead and Nettleship (393).
Ovate-pyriform to elliptical ovate (394). Shape maximizes surface area in contact with brood patch in a bird that incubates in a semiupright position, as well as imparts greater stability on the ledge (387, 395, 396, 397). Recent phylogenetic research implicates body mass and flight characteristics, as well as not nesting in a cavity, as factors related to egg shape in Charadriiformes, particularly Common Murres (398). Birkhead (399), however, argued that these authors over-emphasized the flight characteristics and that it really was incubation aspects that dictated egg shape in murres. Egg shape varies among females, being consistent among years and between first-laid and replacement eggs (395).
Size and Mass
U. a. aalge: Mean mass, Cape St. Mary's, Newfoundland (1931), 103.4 g (range 83–117 g, n = 15; 33); Gull Island (1977), 108.4 g (n = 287; 388); Gannet Islands (1981–1983), 111.5–113.1 g (n = 198–250 depending on year); 29). One egg, 113 g when laid, lost 8 g in 10 d of incubation (33). Size of second or replacement egg averages 9.6% smaller than first (n = 30; 388).
Mean size, eastern North America, 81.0 × 50.3 mm (n = 64; 394); at Gannet Islands (1981), 83.1 × 51.2 mm (n = 197; 29); at Gull Island (1977–1978), 82.7 × 50.9 mm (n = 287; 388). Mean volume index (length × breadth2), Gannet Islands (1981–1983), 215.3–218.9 (29).
U. a. inornata: Mean size, Triangle Island, British Columbia (2002), 85.5 x 50.5 mm (n = 15); mean volume 218.1 ± 15.1 cm3 (37).
U. a. californica: Farallon Islands: 1913 (n = 66) compared to 1968–1970 (n = 29): mean length (mm), 82.52 ± 0.78 SE versus 83.60 ± 1.48; mean breadth (mm), 50.51 ± 0.37 SE versus 50.24 ± 0.64 SE ; mean mass of shell (g), 13.63 ± 0.33 SE versus 12.10 ± 0.10 SE. Mean volume index: 210.5 (1913) versus 211.0 (1968-1970).
Very thick in order to withstand being moved around on rock substrate (no nest). Mean eggshell thickness for 2 colonies in eastern Canada: Machias Seal Island (New Brunswick), 0.77 ± 0.08 mm; Gull Island (Newfoundland and Labrador), 0.75 ± 0.06 mm (400). These values are greater than in previous reports, suggested to be due to decreased use of pesticides in recent years (400).
In the Farallon Islands, changes in thickness between 1913 (n = 66) and 1968–1970 (n = 29) measured as follows: thickness index (mass [g] × 10/length [cm] × breadth [cm]), 3.27 ± 0.06 SE versus 2.88 ± 0.10 SE; shell thickness (mm), 0.70 ± 0.01 SE versus 0.61 ± 0.02 SE. Size not different, but thickness, thickness index, and shell mass 12.8, 11.9, and 11.5% less, respectively, in later sample (401). Eggshells thinner in 1968-1970 in accord with higher chlorinated hydrocarbon concentrations (401). In 1993 sample, thickness 0.68 ± 0.06 SE (n = 19), therefore, restored to earlier levels; compared to eggs from Oregon, 5.4% thicker than collected 1947 but 0.3% thinner than those from 1979 (402; see Conservation and Management: Effects of Human Activities).
Color and Surface Texture
Astonishing variety, with background mostly dark green to blue-green or turquoise with black spots and streaking (38, 365), but also lighter to tan, pinkish, and white; sometimes no spots or streaking (394, 27). According to Gaston and Nettleship (365), proportion of dark green-blue eggs to light color is normally about 50:50. Rarely, reddish eggs occur, likely the result of a genetic mutation in a given female resulting in erythrism (403). In California, intensity of green and blue related to prevalence of euphausiids in diet (which dominate diet in spring, see Diet and Foraging: Diet); lighter colors apparent when euphausiids unavailable as during El Niño, i.e., prevalence of dark colors (using 365 color scale) changes from 53% to 38% when low euphausiid contribution to pre-egg laying diet (27). Adults use color and markings to identify their own eggs; usually successful when given a choice against a foreign egg (404, 286, 405). Strong tendency for a given female to always lay eggs of same color and markings (35, 404, 406; see 395); apparent, too, between first-laid and replacement eggs (395; DGA, DNN, personal observation). Inter-individual variability in egg coloration (and ability to recognize own egg) is an adaptation to high-density breeding (289).
Most often early morning, at least in lower latitudes where dark periods occur, but some throughout day. A few minutes before laying, female stands up off tarsi to raise cloaca from ground; body vertical, facing rocks or cliff walls; wings held loosely down at sides; tail between legs (386). Appearance of egg preceded by convulsing, sometimes pecking at cloaca, and finally straining upward several times. Narrow end of egg emerges first. With tail down, female plops forward, pushing egg beneath with blunt end toward cliff wall.
In hours before laying, female exhibits “nest” building behaviors (386); includes picking up objects (pebbles, feathers) and placing by side, and using feet to scrape any loose material outward from beneath site where egg is to be laid. These behaviors occur in bouts, sometimes repeatedly.
Onset of Broodiness and Incubation in Relation to Laying
Egg incubated as soon as laid; normally continuously thereafter. During periods of extreme food shortage (El Niño), eggs may be left unattended, but often are lost to predation or disturbance by neighbors. Parents that have lost an egg sometimes adopt a neighbor's egg if left unattended, although it rarely is retained or hatched (405).
One, in center midline of belly, both sexes (same as Thick-billed Murre Uria lomvia, Razorbill Alca torda, and Great Auk Pinguinus impennis; 192). In Barkley Sound, British Columbia, regressing patches visible on many males accompanying chicks from early July to early September (H. R. Carter and S. G. Sealy, unpublished data); thus, patch regression, begun after hatch, not completed until late chick period.
Averages 32.4 d ± 1.4 SE (range 26–39, n = 1,202) on Farallon Islands (27); almost identical to data from elsewhere (cf. 387, 327). However, slight interannual variation related to persistence of incubation, in turn related to food availability (i.e., adults less attentive and incubation slightly longer when food sparse; 27).
Upright incubation posture similar to that of Great Auk, contrary to Razorbill (which lies down); related to pyriform-shaped egg (192, 396, 397). Incubation shared equally between sexes (407, 298); females incubate more during night with changeover occurring in late afternoon/evening then again at first light in Labrador (298), whereas in other breeding locations either sex broods at night (Great Island, Newfoundland: 299). At least one changeover during day to allow both members time to feed and bathe (DGA). Changeovers not likely to occur at same time each day, and not synchronized with neighbors; at Gannet Islands, Labrador, incubation shifts averaged 17 h (range 1–38; 298).
Hardiness of Eggs against Temperature Stress: Effect of Egg Neglect
No data. In central California, eggs left unattended for hours (which happens only under periods of extreme food shortage); if not taken by gulls, often still hatch (DGA). One egg abandoned mid incubation for 4 days, subsequently hatched (T. R. Birkhead, unpublished data)
Preliminary Events and Vocalizations
Embryonic growth rate rapid compared to other birds (408). Embryo mass about 1 g at 7 d of age, growing slowly to 8 g at 20 d; thereafter growth rate increases markedly and embryo weighs 30–40 g by day 27 (388). Mass of pipping chick directly related to embryo mass; in pipping eggs (n = 11; Gannet Islands), egg mass averages 100.0 g, chick wet mass 75.8 g, including remaining yolk of 17.6 g; values similar to Thick-billed Murre and Razorbill, but greater than for Atlantic Puffin (Fratercula arctica), whose chick remains in the nest much longer and lacks prolonged parental care after fledging (393).
Hatching begins with pipping about 24–36 h before chick emerges. Calls of chicks clearly audible. Parents call to pipping eggs and sometimes even offer fish; vocal recognition may begin at this time (286; see Sounds: Vocalizations).
Shell Breaking and Emergence
On average, 2.7 d (n = 53) for chick to emerge from egg after first cracks appear (359). Once egg pipped, chick emerges within 24 h; incubating adult sometimes assists process by pecking and breaking eggshell around opening. Rarely observed, as chick is brooded closely.
Little variation in hatching success observed over 12 seasons at Farallon Islands, central California: mean for first eggs 85% (range 80–93%, n = 1,506, excluding intense El Niño in 1983, when it was 32%; 27). Little variation also at Castle Rock, northern California, averaging 73.6% over 11 yr (232). Success of first-laid eggs much higher than replacement eggs (67%). In addition to those that hatched, an average 12% lost and 3% addled (27). Similarly, at Gannet Islands, 1981–1983, mean hatching success of first eggs ranged 82–89%, and of replacement eggs 36–50% (327). At Great Island, hatching success of first eggs 72.7% (1983, n = 162; DNN) and 80% (n = 95, 1998–2002; AES), and replacements 69.2 % (n = 13; DNN). Rates in Alaska seem slightly lower, on average, for both first eggs (34–76%) and replacements (47–65%; 409). In presence of aerial predators, such as Bald Eagles, which cause adults to temporarily abandon ledges, hatching success reduced markedly by gulls swooping in to take exposed eggs (340; see Behavior: Predation).
Parental Assistance and Disposal of Eggshells
No active attempt on part of parents to remove from breeding site; shells become crushed or fall from ledges; egg membrane (robust) often remains at site for several days after hatching (H. R. Carter, unpublished data; DGA, DNN, AES).
Condition at Hatching
Fully covered with down (length 8 mm on head, 11 mm on body), with remnants of yolk sac still attached. Feet and legs disproportionately large; tarsus about 45% that of adult (388). Can “stand” on tarsi (as do adults) within a day of hatching (DGA, DNN).
Growth and Development
Six days after hatch neossoptiles disappear, replaced by contour feathers; egg tooth faded, and yolk sac reabsorbed; by 12 d old, contour feathers well developed. Rate of growth (daily mass change), first 20 d: r = 0.049 at Gull Island, Newfoundland; 0.062 at Skomer Island, Wales; and 0.041 at Farne Islands, Scotland (388). Linear growth during first 16 d, at 8.8 g/d (Gull Island; 388) to 9.3 g/d (Skomer Island; 244). Body mass at 16 d about 200–216 g (410, 290, 388; see below for departure mass).
Exhibits certain characteristics as a means to reduce likelihood of falling from breeding ledges: reduced tendency to wander, faces or is “attracted” to wall, avoids light (i.e., negatively phototrophic), avoids cliff edge, and delays flight practice to near last day on ledge (411 and references therein).
Sex Ratios and Sex Allocation
Differential allocation to male and female chicks: male chicks were fed more often than females in Witless Bay, Newfoundland (412), but female chicks were heavier than males at Hornøya, Norway (413). More cliff time during pre-lay period and single parent post-fledging care were suggested in the former case as selecting for males being larger and/or in better condition; whereas post-fledging competition for breeding sites is suggested for females in the latter case.
Males and females spend equal time at colony 2–3 wk before egg-laying, then females begin to visit less, males more (Birkhead 1978a; 407). This pattern is prevalent among many seabird species (with females storing sperm but which attenuate over time). Yet in single-egg species, the ratio of sperm to ovum in females is exceedingly high. This high ratio may help to insure fertility given that female colony attendance decreases just before egg laying (414). Both sexes incubate egg and brood chick equally (298). Since females feed chicks more than males in some colonies (varying with pairs and year; 407, 303, 415), parental investment by sex to this point similar. Males depart with chick, and females continue to visit colony for several weeks, staying longer in European colonies than at Witless Bay colonies in Newfoundland. Actual division of labor overall appears equal considering (1) attendance (i.e., defense, feeding, and guiding) of chick post-fledging (male) and (2) greater investment in egg-laying and defense of breeding site from prospectors/competitors after fledging, assuming a carryover effect to next breeding season (female). On average, male probably best choice for both tasks, owing to greater size and aggressiveness, as is the case for Thick-billed Murre (Uria lomvia; 416, 365). However, prolonged care only by male suggests enhanced survival of young when accompanied by male rather than female. Defense of breeding site from competitors prior to fall exodus (essential to subsequent breeding success) left to female, who may be in poorer condition.
Although one adult in each breeding pair is almost always with the egg or chick (but see 232), there is considerable variation in the amount of time that both parents co-attend at the breeding site. Pairs spend more time together under favorable feeding conditions (417, 209, 301, 302, 303), and within the range of conditions during this time period, this variation in co-attendance time did not significantly impact chick-provisioning rates or chick survival. High levels of co-attendance were thought to allow more ‘loafing’ time for non-brooding partners. Alternatively, partners may negotiate more under good conditions, attempting to do more of the less energetically expensive parental activity (brooding) without pushing their partners towards desertion as would be more likely under poor feeding conditions (304). Supporting evidence for the brooding negotiation hypothesis in relation to co-attendance time: (1) longer co-attendance times under good conditions occurred because returning birds waited longer before departing when brooders prevented an exchange, and (2) low-quality birds delayed brooding reliefs longer than high-quality birds. Furthermore, brooders signal intention to delay the exchange by not reciprocating their partner’s allopreening (307).
At first, chick visible only when parent offers food; by time of site departure, chick usually stands next to parent. At least one parent always present, except under extreme food shortage (see Behavior: Predation). At Gannet Islands, Labrador, daytime brooding shifts average 4 h (range 1–14); those that include the night average 12 h (range 7–20; 298). In rare cases, chicks left alone take advantage of neighboring adults that have lost their chick; failed breeders known to brood and even feed such chicks (243); allobrooding only observed on Great Island, Newfoundland, in the year with the best feeding conditions (1999 in years from 1997 to 2003; AES).
Parent arrives with fish in bill (head in throat, tail toward tip of bill), calls, and lowers head next to chick as it takes over brooding (other parent shuffles or is pushed aside; DGA, DNN, AES). Chick calls in answer. Parent shields fish from neighbors with partly unfolded wings. Chick grabs fish in bill, then works with short “bites” to orient head-first to be swallowed. Young chicks may not take fish immediately, but almost always within a few hours. Neighboring adults may steal large fish, or its tail, while parent waits for chick to feed. Among older chicks (>1 week), fish usually taken immediately. If fish is long, tail may project from chick's mouth, but disappears as head digests. When food sparse and diet diverse (e.g., El Niño), chicks ignore inappropriately shaped prey (111).
Chicks fed a single fish several times daily; feeding rates vary with prey size, caloric value, and availability, both within and between days, and by year (see 171, 83). At Farallon Islands, average number of fish/d, 1973–1983, 2.2–5.0, with time between feeds 141–218 min; fewer feeds and longer feeding intervals occurred during years of food shortage (see also 171). Daytime trip durations (rough measure of brooding shift length, 2–3 h under good foraging conditions; 1998, 1999), ~ 4 h when capelin arrived inshore after the first week post-hatch, then decreased to ~ 2h after capelin arrival (Great Island, Witless Bay, Newfoundland; 303). Feeding rate highest in early morning and evening crepuscular periods (27; see Diet and Foraging: Feeding). Frequency of deliveries and type/size of prey affected by stormy seas (368, 418). At Gannet Islands, Labrador, chicks fed, on average, 4–5 times each day during 15-h day, with mean feeding rate significantly higher in 1982 (1.15 meals/chick/4 h; n = 11) than 1983 (0.89 meals/chick/4 h; n = 14), and duration of foraging trips longer in 1983 (93.9 min; n = 161) than 1982 (78.0 min; n = 167; 171). In 1996–1997, 2 distinct peaks in delivery of food to chicks: 06:00–08:00 and a lower, but broader peak 15:00–18:00 (187). At Gull Island (1978), Witless Bay, Newfoundland, chicks also fed throughout day (14 h long), but peak occurred 08:00–16:00, and chicks fed on average 3.3 fish/d (n = 89; 359). Peak in early morning in 1997–2003 for Great Island (AES), likely corresponding to diel vertical migration (DVM) of capelin, such that murres could obtain prey with shallower dives just before sunrise and after sunset, but would need to make deeper dives during the rest of daylight hours (189). Feeding rates at Farallon Islands, California, did not vary between years, which may indicate that parents buffer slight variation in prey availability by investing more time in actual foraging (417, 419, 235, 302; see Demography and Populations: Measures of Breeding Activity).
Feeding rate and caloric intake also vary with chick age. At Gannet Islands, Labrador, feeding rate for chicks 1–2 d old about 2 fish/d (225 kJ/d); maximum at 9–10 d, with 4–5 fish/d (400–480 kJ/d); total intake over 24-d chick-rearing period 7,021–8,259 kJ (296–336 kJ/d), but intake varies between years (171). Under relatively good conditions at Great Island, Witless Bay, Newfoundland, chicks received approximately 4 fish/d in weeks 1 and 3 after hatching with a peak of 6 fish/d in the second week; in a year with delayed capelin arrival inshore, chicks were fed 2 fish/d in week 1 and 4–5 fish/d thereafter (303). Lower provisioning rates recorded under poor foraging conditions in Witless Bay colonies (420, 279: ~2fish/d). Feeding rate at Isle of May, Scotland: 4.1 fish/d, totaling about 30 g (421); Sumburgh, Head, United Kingdom total: 38 g, 6.3 fish/d in good year, 3.0 fish/d in poor year (301). Captive murre chicks ate up to 130 g/d (410) with fledging mass only about 20% higher than for chicks in the wild (421).
Although pairs vary in whether males or females have higher provisioning rates (304), female Common Murre provision at higher average rates than males (Great Island, Newfoundland , Isle of May, Scotland ). Some measures of foraging effort did not differ between males and females during the biparental pre-fledging chick-rearing period (dive depth, dive and pause duration ; time spent diving, patch quality ), but Thaxter et al. (415) found that males took longer trips and dove more often than females. Thaxter et al. (415) suggested that since females provision more than males, the additional dives by males may be for self-feeding in preparation for the post-fledging male-only care. This may also be true in Witless Bay, Newfoundland, given the higher female provisioning rate (303), but equivalent foraging effort (266), as has also been found in Thick-billed Murre (283).
Breeding Site Sanitation/Carrying of Eggs or Young
Not known to occur.
Not known to occur, but failed breeders can occasionally brood and very occasionally feed chicks of neighbors (Tschanz also recorded alloparental behavior: 243; M. P. Harris and S. Wanless, personal communication; AES, personal observation); most common in a good foraging year (AES).
Brood Parasitism by Other Species
Not known to occur as a reproductive strategy.
Employs “intermediate strategy” of chick development in Alcidae (e.g., Synthliboramphus chicks depart with parent just after hatching, but puffin [Fratercula spp.] and guillemot [Cepphus spp.] chicks remain in nest until independent), likely to reduce energetic costs of chick rearing (422, 111) and competition for food in large, highly synchronous breeding populations. Chick age at departure: Farallon Islands, averaged 23.5 d (1972–1981 [n = 1,175]; 27); Gannet Islands, 23.9 d (1981–1983 [n = 394]; 29); and Gull Island, 20.2 (1977 [n = 40]; 359). At Farallon Islands, colony-chick period slightly longer in food-poor years, compared to food-rich years; slightly shorter among late chicks (27). Inter- and intra-year variation seen also at Gannet Islands, 1981–1983, with departure age negatively correlated with hatching date (29). See 423 for summary of European data.
Length of colony-chick period a compromise among several factors (422, 424): (1) parental need to find food, if being depleted nearby (through interference or exploitative competition); (2) a limitation on egg size and, thus, degree of precocious development, owing to factors related to wing-loading (precocious hatching would allow parent to take chick to food even sooner); and (3) predation pressure, to which chicks must be developed sufficiently to glide from ledge and to dive in order to escape avian predators. A dynamic model incorporating differential growth and mortality in breeding-site versus ocean chick rearing, and relation between chick size and survival, correctly predicts chick mass at departure and age (425). An additional factor is the energetic cost of bringing food back to the colony for a bird with high wing loading, such that it may cost less to take the chick to the food than to continue bringing fish to the chick at the colony.
Departure from the Breeding Site
Substantial variation in growth and age at departure, as chicks and parents adjust departure timing to synchronize with other colony members, and to meet their own needs. A model to investigate influence of growth rate and hatching date on fledging decision in alcids, including murres, focused on “the differential growth benefits and mortality costs of the pre- and post-fledging habitats (nest and ocean)” to explain the declining mass of late-hatching chicks (426). Model predictions confirmed by observations (see above; 427). Body mass at colony departure also related to food availability, both between and within colonies (428), and yearly differences have been documented in relation to food availability (256). Fledging body mass does not affect chances of subsequent survival of chick, likely because chick must develop substantially more before it becomes independent regardless of departure mass (429). For most chicks, mass may be less important than degree of development and locomotion at departure for helping to ensure survival at departure and for first few days at sea.
Body fully feathered, except some down on head; among flight feathers, only wing coverts grown (see Appearance: Molts). Average body mass at departure as follows:
U. a. inornata: Cape Thompson, Alaska (1960), 179.9 g (n = 6; 16); St. Paul and St. George islands, Alaska (1976), 175–205 g (n = 9), (1977), 160–185 g (n = 14; 428); Middleton Island, Alaska (1978), 203.8 g (n = 374; 430); Triangle Island, British Columbia (2002–2007), varied from mean of 170–230 g, depending on year (n = 9–14; 37). Those that took longer than a day to reach the ocean lost body mass at 17.7 g/d; body mass lower at a new, expanding colony (190.7 g, n = 86) compared to other colonies (207.8 g, n = 288), perhaps related to younger parents (430).
Departure mass, as observed at Stora Karlsö, Sweden, declined among late chicks: mean mass similar among chicks that depart 10 d before to 3–5 d after mean date (ca. 256 g), but decreases to 222 g about 15 d after mean date (427, 431). Significant yearly differences linked to food abundance at Hornøya, Norway (range 220–290 g; 432).
According to L. M. Tuck (38: 159), “If the land-coming of murres is exciting, the sea-going is even more so. For a few days before the chicks are ready to go to sea, adults congregate at the base of the cliffs and call excitedly . . . a milling congestion of birds in which numbers and noise are outstanding. Such early groups are probably non-breeders or birds which have lost their eggs or young, but at the critical time of sea-going they are joined by increasing numbers of breeding birds.”
Departure highly synchronous, but varies with latitude and year. At Gannet Islands, Labrador (54°N), mid-80% of departures took 4 d in 1981, and 6 d in both 1982 and 1983 (171); at Farallon Islands, California (38°N), mid-80% took about 5–10 d, 1972–1982 (27: Fig. 8.4). Therefore, departure synchrony even greater than egg-laying synchrony owing to loss of late-laid eggs and shorter chick-rearing period of late-hatched chicks (see above).
Dates of ledge departure vary (Figure 2). At Farallon Islands (possibly most variable), median date ranged 5–25 July 1972–1982 (27: Fig. 8.4). At Gannet Islands, median 9–13 August 1981–1983 (171); and Great Island, Newfoundland, 19–21 July 1983–1984 (DNN). At Isle of May, Scotland, median date ranged 23 June–9 July 1981–1986 (433). At Stora Karlsö, Baltic Sea, average ranged 25 June–5 July during 1972–1977, but earlier at 21–27 June during 2000–2006 (434).
When about 48 h from departure, chick exercises wings and moves away from breeding site; actual departure regulated by male parent (DNN, 29). Almost always leaves after sunset (or darkest part of day where daylight is 24 h), but before complete darkness (some late chicks may leave during day; 38). Avoids fledging during high winds and rough seas (29, 27). Giving Departure Call (see Sounds and Vocal Behavior: Vocalizations), begins to move toward water with male parent. In aborted departures, parent may brood chick at new location until next evening. During actual departure from breeding cliffs, behavior of parent varies greatly. If breeding site on a ledge, chick usually jumps first followed, almost touching, by adult; sometimes adult flies to water beneath and calls to chick, with constant “dueting” between parent and chick until reunited. Chick leaps and breaks fall by fluttering partly developed wings; some mortality if chick hits sharp rocks. If breeding site on a steep slope, chick walks and tumbles; male parent accompanies chick closely; if left unguarded, fledgling likely to be taken by predatory gulls once away from subcolony.
On open coasts, once they reach the shoreline, chicks often swept away by swells, often with parents immediately in front calling loudly and frequently; once chick enters water it swims off. If parent absent or distant when entering water, chick mobbed by other adults until proper identity established through voice recognition (see Sounds and Vocal Behavior: Vocalizations). At this stage, tarsus length 80% adult size, in contrast to wing chord and culmen length, which are 20% adult size (388). See Tuck (38) and Whitt (435) for especially detailed accounts of chick-leaving.
Captive later-hatching chicks fed ad libitum grew faster than early hatching chicks, but grew more slowly when food was restricted (436). Wing growth may be prioritized over mass gain under poor feeding conditions, possibly to facilitate early fledging (Great Island, Newfoundland, 437; captive chicks, 436).
Association with Parents or Other Young
Accompanied at sea by male parent, which guards and leads it to prime foraging areas and provides it food (422, 424, 24); duration of parental care uncertain, believed to last at least 1–2 mo (438, 387).
Ability to Move, Feed, and Care for Self
Swims strongly on legs and feet disproportionately large relative to body size (see above). Initially dives weakly, staying below 10–20 s (DGA).
Little known about the life history of young birds between departure from colony and first visits to colonies several years later. Rate of growth during first month at sea, as measured by change in wing chord, culmen length, and culmen depth, much faster than rates determined for chicks at colonies (439); no difference in rate of body mass gain (440). After departing colony, chicks gain about 15 g/d, reaching 90–95% adult mass by 45–60 d post-departure (438, 440). Some dependent chicks in central California still being fed by adults during autumn (September), even though body mass greater than that of parent (DGA).
Age of independence not known, probably 2–3 mo post-departure (438, 387); may be capable of flight at 46 d (441 and references therein). During some years in central California (January–February; 4 mo post-cliff departure), however, appreciable number of adults (molting into or in breeding plumage) seen paired with smaller, winter-plumaged bird, possibly still parent-chick pairs (DGA). If correct, then parent-chick association may sometimes exceed 2 mo. At Isle of May, Scotland, some pairs that fledged young successfully do not reappear at colony during autumn (381), which indicates that male parents may still be with their chicks at sea. In Barkley Sound, British Columbia, many fully independent juveniles observed diving, no longer attended by adults, in September and October; no parent-chick pairs observed after October, when many adults had completed Prebasic molt, regained flight, and departed (H. R. Carter and S. G. Sealy, unpublished data).
Mortality increases soon after cliff departure (August–September), but not again until November–February, which must correspond to first months normally independent of parents (see Demography and Populations: Causes of Mortality). Review of immature survival in European colonies (United Kingdom, Sweden) and Farallon Islands, California, indicates that survival of 1-yr birds is ~0.5, and increases to more than 0.8 for 3–4-yr birds (442).