Mating System And Reproductive Behaviour Of Ad Lie Penguins Biology Essay

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First to return to the breeding grounds are the males. They return to the previous years nest, while it is rare for penguins to actually fight, preferring to give threat displays, if the returning male finds another male occupying his site he will fight to regain his preferred nesting site (Penny, 1968). In stand-offs over nesting sites, the more experienced birds have a tendency to win, preferring sites in the middle of the colony as these offer better protection form marauding skuas (Stercorarius maccormicki (Saunders, 1893)) (Muller-Schwarze, 1984). Younger Pygoscelis adeliae are relegated to the margins of the colonies, however this leads to reduced success rates (Penny, 1968).

The female Ad‚lie penguin can arrive within as little as a day of the male. The male will have begun constructing the nest from pebbles, frequently stealing pebbles from unguarded neighbours nests. They will carry on adding pebbles to the nest throughout the breeding season, even after the chicks are hatched (Muller-Schwarze, 1984).

While nesting Ad‚lie penguins tend to face between other nests, this reduces stress and conflict, preserving energy for breeding and guarding chicks (Spurr, 1975).

Courtship

Courtship among new formed pairs lasts from seven to twelve days. The mating ritual may include the 'ecstatic' display, standing erect pumping his chest and issuing a loud braying noise while stretching his flippers backwards, the female responds with the 'oblique stare bow' arching the neck, lowering the head then slowly raising the head. Birds which were paired the previous year will perform 'loud' or 'quiet' mutual displays. Newly paired birds may produce no eggs from the mating or form a true pairing and produce chicks (Muller-Schwarze, 1984). Pairs which reunite each season have a higher rate of breeding success then birds which split, usually due to the death of a mate, and must therefore seek a new mate, as reunited pairs can commence breeding quicker (Penney, 1968).

Extra Pair Copulations (EPC's)

EPC's take place when a monogamous male or female deem that their reproductive success can be enhanced, without the risk of losing their mate, by so doing. For Pygoscelis adeliae and other seabirds where both parents are required to raise the chick EPC's are believed costly. For penguins where the one parent must stay with the egg/chick while the other feeds EPC's are particularly risky. A study by Pilastro et al. (2001) showed that while female Ad‚lie penguins copulate more often with their paired mate, 10% of chicks were not sired by the paired male which was providing parental care for them. Research revealed that between twenty-one and thirty-two percent of females mated with more than one male during the breeding season. Evidence suggested that the females engaging in EPC's acquired extra pebbles for the nest from these encounters. As the male must remain on the nest to protect it, it would be hard for them to thwart these EPC's in a crowded colony (Pilastro et al., 2001).

The Price of Breeding

Due to the extreme location, feeding restrictions and distances involved, Ad‚lie penguins are constrained in their reproductive endeavours. During the initial stages of the breeding season Ad‚lies are reliant on their fat reserves for energy. The amount of fat stored at the beginning of the breeding season bears a direct correlation to reproductive success. These factors have contributed to a predictable, timed breeding season (Vleck and Vleck, 2002). From the time of arrival males have been shown to survive for up to fifty days before returning to the sea to feed. This requirement may influence the decision whether to breed or not. Females who laid eggs were discovered to have higher body masses then those females who engaged in courtship but did not produce eggs. This suggests that body condition may impact on a birds ability to produce eggs. The condition of the parent would also impact on their capacity to care for any chicks (Vleck and Vleck, 2002). As the life span decreases in relationship to the number of breeding occurrences and Ad‚lie penguins can survive to reach twenty years, it suggests that not breeding when not at peak fitness increases the potential to successfully chicks in coming years (Vleck and Vleck, 2002).

Guarding

Ad‚lie penguins usually lay two eggs in a brood, after they are laid the female returns to the sea to feed while the male takes over incubation duties. The female remains at sea for about fourteen days, returning to relieve the male who leaves to feed but only for about ten days while the female incubates. When the male returns he will incubate the eggs until they hatch in December, when the female again returns (Ainley, 1978). Pygoscelis adeliae chicks are nidiculous this requires that at least one parent is in attendance. The parents have a brood patch on their chest where the chicks are held maintain body temperature the parents alternate protecting the chick every three to four days during this time. When the chicks are three weeks old they are big enough to move to a crŠche where they gather en masse for protection from predators and thermoregulation. While in the crŠche the parents return every two or three days to feed them, using vocal recognition to identify their chicks. This continues until the chicks fledge in February.(Muller-Schwarze, 1984).

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