Breeding and Life Cycle

With respect to KING GEORGE ISLAND, South Shetlands, where THIS STUDY was conducted, however, populations monitored at Admiralty Bay (location of SSSI 8, now ASPA 128) from 1976 to the present were highly variable but stable until the late 1980s, and then declined sharply. For this area, mean population counts “from 1990 to the present” are lower than mean counts “for 1976 to 1988” by 30 % (Penguin CAMP Report, August 1998, as quoted in CBSG Penguin Conservation Workshop, Ushuaia 2004) to 35 % (SCAR 2001).

As for Potter Peninsula, AGUIRRE (1995) reported 14,554 pairs of breeding Adélie penguins at STRANGER POINT (SSSI 13/ ASPA 132) whereas (personally witnessed) censuses in 2000 and 2001 yielded approximately 7,300 and 5,500 breeding pairs, respectively. This was confirmed by SANTOS & al. (2004), who reported a continuous decrease from 1998 to 2002, when the number of breeding pairs totalled only 49 % of those counted in 1995. Even though these figures might not be entirely compatible (the 2000/ 2001 censuses were effected by counting nests with eggs and nests occupied; the author of THIS THESIS does not recall census methods poster-presented by SANTOS & al. 2004), the general trend for this area appears to be a declining one.

The Adélie penguin has been classified as being susceptible to human disturbance, with local decreases in population size caused by the construction of research bases in the Ross Sea, at Cape Royds, and at Terre Adélie (= Adélie Land), though stricter regulations on human activity have resulted in the colonies’ returning to former numbers of breeding pairs (HARPER & al. 1984;

JOUVENTIN & al. 1984; both quoted in WILLIAMS 1995). The Penguin CAMP Report (August 1998, as quoted in CBSG Penguin Conservation Workshop, Ushuaia 2004, p. 42) lists the following existing and potential threats to the Adélie penguin in the Antarctic Peninsula area (boldface added here):

a) the persistent, restricted location of commercial krill fishing in waters adjacent to breeding populations during their breeding season (AGNEW & PHEGAN 1995, as quoted in CBSG Penguin Conservation Workshop, Ushuaia 2004, p. 42),

b) oil pollution and other marine pollutants such as organochlorines,

c) direct human disturbance, especially in the vicinity of stations (and particularly on KING GEORGE ISLAND) and at sites frequently visited by tourists.

Table 3-1: Adélie Penguin Life Cycle. With respect to arrival until egg-laying, average number of days is given for KING GEORGE ISLAND (KGI) specifically. Extracted from WILLIAMS (1995).

Month Activity Average Number of Days

Sept./ Oct. arrival till egg-laying 21 (KGI), may be shorter at other locations Nov./ Dec. incubation period till hatching 35-39 (1^st eggs in 2-egg clutch); 33-38 (2^nd eggs) December hatching till end of guard stage 18-27

January crèche stage till fledging 30-43

Feb./ Mar pre-moult feeding highly variable: a few days to over a month Mar./ April moult till leave for sea 15-23

May-Sept at sea (migratory stage) remainder

At SSSI 13¹⁹ (now ASPA 132²⁰) (see maps in section 3.2), the largest sub-colony (in which the study presented here took place) is situated on an ‘elevated plain’, while the spatial pattern of small sub-colonies (fig. 3-23) reflected the area’s topography: the nests were concentrated on little mounds which lost their snow and ice cover more rapidly than their surroundings, and were thus accessible for nest building earlier than the lower plains around them. According to TRIVELPIECE

& TRIVELPIECE (1990), site-fidelity on KING GEORGE ISLAND is high: 98.9 % (98.1-100, n = 4 years) of males and 65.5 % (61.8-72.9) of females returned to the same nest in successive seasons; and in 6 years less than 0.1 % of females and no males were found breeding at a colony different to that in the previous year. In general, AINLEY & al. (1983) reported that of those birds that survive to breeding age, 96 % breed at their natal colony, the remaining 4 % at an adjacent colony; 77 % of the birds they studied bred within 100 m of their natal site. Although the Adélie is typically monogamous (WILLIAMS 1995), pair-fidelity has been found to vary between seasons (e.g., KING GEORGE ISLAND: 62 % of birds retained the same mate between years); among other things, fidelity depends on synchronicity of arrival and interseasonal survival of both partners. Furthermore, a latitudinal variation has been observed:

“The shortness of the breeding season and the consequent importance of arrival and breeding cycle synchrony are no doubt the reason why mate fidelity is low in Adélie penguins of the southern Ross Sea, compared with birds of lower latitudes and with other long-lived seabirds.” (AINLEY 2002, p. 146)

While the male selects the nesting site and initiates the nest-building, both partners contribute to completion and maintenance of the nest once pair formation has occurred. The nest consists of a shallow scrape surrounded by, and lined with, pebbles. These pebbles are a constant source of conflict between incubators and roaming conspecifics, as all the nests in a colony are continuously repaired and added to. Not infrequently, the pebbles added to one’s own nest are obtained from the nest of a momentarily inattentive neighbour (MORENO & al. 1995a, b; LEVICK 1914; SLADEN 1958).

The mean inter-nest distance found on KING GEORGE ISLAND (43.2 ± 1.3 cm) is smaller than at other locations (e.g., 78-108 cm at Cape Crozier; WILLIAMS 1995). Generally speaking, Adélie territories within a colony are small and tightly packed. As AINLEY (2002, p. 74) puts it:

“[T]erritories are contiguous. That is, the outer edge of one territory abuts the outer edge of at least one other territory. If it stretches full length, a penguin sitting on its nest can catch and lock its beak with that of its neighbor [sic]; also stretching full length from its nest.”

19 Site of Special Scientific Interest 20 Antarctic Specially Protected Area

Once ashore, both birds remain at the nest until egg-laying (mean time between arrival and laying of first egg: 21 d for KING GEORGE ISLAND, tab. 3-1). As in other penguin species, copulation occurs many times during the pre-egg stage, but coition is often incomplete (MARCHANT & HIGGINS

1990) and may – especially in inexperienced breeders – lead to the deposition of infertile eggs.

Egg-laying is highly synchronous, and 50 % of the clutches are initiated over a six-day period.

Adélies usually lay two eggs, but a third egg may be ‘added’ as a substitute for a first egg if the latter is lost or removed within 24 hours of laying (ASTHEIMER & GRAU 1985, quoted in WILLIAMS 1995;

TAYLOR 1962). If an entire clutch is lost, however, no replacement occurs, possibly because of the short breeding season (SLADEN 1958; TAYLOR 1962). Mean clutch size is further influenced by the age of the female (among three-year olds, a significantly greater proportion lay one-egg clutches), fat reserves (deduced from late laying date after unusually late arrival which indicated overly difficult migration caused by heavy sea ice conditions; AINLEY 2002) and relative location of the nest (SPURR

1975a, TENAZA 1971), with the proportion of two-egg clutches increasing from isolated to peripheral to central nests. Mean egg size at four locations (reported in WILLIAMS 1995) varied between 68.4 and 70.5 mm of length and between 54.2 and 56.2 mm of breadth. Mean egg weight ranged from 113.2 to 124 g. First eggs are significantly larger than second eggs (YEATES 1968). SPURR (1975c) found the laying interval between first and second egg to average 3.0 days. Full incubation does not begin until the second egg is laid, and a hatching interval of 1.4 days indicates an equivalent of only 34 h of (discontinuous) incubation during the three-day laying interval (TAYLOR 1962; SPURR

1975c). Both sexes incubate in alternate shifts, usually starting with the male²¹, although reverse incubation patterns have been reported (e.g., TAYLOR 1962). The timing of the change-overs (nest relieves) may also vary; two long shifts and a third shift of medium-length (e.g., SLADEN 1958: 13, 15, 8 days; TAYLOR 1962: 11, 11, 8 days) followed by several short ones are most commonly observed, but the combination of two long shifts (16.6, 12.3 days) followed by several shorter ones is not unknown either (DAVIS 1982). Annual variation in shift length has been suggested to be linked to sea ice conditions (with shorter shifts observed in years of earlier break-up of sea ice, YEATES 1968) or food availability (AINLEY 2002). For KING GEORGE ISLAND, TRIVELPIECE & al.

(1990) found the total number of shifts ranging from 3 to 7. The average incubation period lasts 35-39 d for first eggs and 33-38 d for second eggs (tab. 3-1). MÜLLER-SCHWARZE (1968) and DERKSEN

(1977) suggested a circadian rhythm in some activities of Adélie penguins during incubation, while YEATES (1971, as quoted in DERKSEN 1977) found no such pattern. Hatching is typically asynchronous (eggs hatch on average 1.4 d apart within a clutch). Hatching success varies between years (e.g., DAVIS 1982b, egg losses due to nest desertion: 1^st year of study = 27.5 %, 2^nd year = 47.5 %) and localities. Addled or infertile eggs, nest desertion, and predation have been listed as causes for egg failure. After hatching, the chicks are guarded and brooded²² continuously by one parent for 18 to 27 days. Change-overs during guard stage occur every day or twice in three days (TAYLOR

1962), and guard duties are shared roughly equally by males and females (spending 55 % and 45 % of the time guarding, respectively). Guard stage is followed by crèche²³ stage, during which the chicks aggregate in small groups (10-20 birds), while both parents leave the colony in search of food. The returning parent feeds the chicks; at KING GEORGE ISLAND, chicks were found to receive 0.99 feeds per day, with a mean feeding interval of 24.3 ± 0.8 hrs (TRIVELPIECE & al. 1987).

Mean age at fledging ranges between 48.4 and 61.3 days (TAYLOR 1962; AINLEY & SCHLATTER

1972; LISHMAN 1985). Chick loss may occur through predation (particularly by Skuas, Catharacta

21 while the female replenishes body supplies after egg-laying

22 Adélie chicks do not develop thermoregulation until about 10 to 15 days of age (GOLDSMITH & SLADEN 1961).

23 A crèche is defined as three or more chicks closer to one another than half the inter-nest distance (AINLEY 2002). The term crèche is meant to imply simply a collection of young. There are no ‘guardians’ of the crèche (SLADEN 1958).

spp.), starvation (not enough food for one or both chicks), and nest desertion (parents failing to return). Generally, chicks in peripheral nests are more prone to predation than those in central nests. At KING GEORGE ISLAND, breeding success (in number of chicks fledged per nest) is reported as 0.98 (WILLIAMS 1995). After the chicks have fledged (Feb.-Mar.), the adults return to the sea to build up their fat reserves during a pre-moult period (the duration of which ranges from a few days to more than a month), before moulting requires them to remain ashore or – more commonly – on ice-floes, and to fast for 15 to 23 days. According to PENNEY (1967), the period spent on land/ ice-floe includes the pre-moult (5.1 d, in which the penguin’s body prepares for shedding its coat), moult (14.9 d, in which the feathers are shed and the new ones pushed out), and post-moult stage (2.5 d, which the birds mainly spend preening and oil-preening their new plumage). During the time spent ashore/ ‘a-floe’, birds lose approximately 45 % of their initial mass at a rate of 151-193 g per day (PENNEY 1967). Peak numbers of moulting adults have been recorded in early March (WILLIAMS 1995), with unsuccessful breeders moulting earlier and immatures completing their moult before non-breeders and breeding adults. In a study at Cape Crozier, the modal age of first breeding was five to six years (AINLEY 2002), with the average age for females being 5.0 years and for males 6.2 years. Females, but not males, may breed at three years of age.

Survival varies annually; and mortality is higher in females than in males (AINLEY & DEMASTER

1980) so that the sex ratio becomes male-biased with age, changing from 1:1 for two-year-olds to 1:0.4 in 14- to 16-year-olds (AINLEY & al. 1983). Most adult mortality occurs during the winter (SPURR 1975c). Moreover, not all penguins that survive and return to the colony will also return to breed. SPURR (1975c) reported that during an observation period of three years, between 4 % and 26 % of the males and 2 % and 18 % of the females which had previously bred returned the following year but did not breed.

3.1.4 Ethogram

of Adélie Penguin Behaviour During the