A. Sexual maturity
1. Like most seabirds, penguins tend to be long-lived. They may take three to eight years to reach sexual maturity (Stonehouse, 1975).
2. With some of the smaller species, breeding may begin at three or four years, but most larger species are not accomplished breeders until much later. On average, breeding does not begin until the fifth year, and a few males do not breed until the eighth year (Simpson, 1976).
B. Mating activity
1 . Breeding seasons differ from species to species.
a. Most species have an annual breeding season - spring through summer (Marchant, 1990).
b. The king penguin has the longest breeding cycle of all the penguin species, lasting 14 to 16 months. A female king penguin may produce a chick twice in every three breeding seasons (Sparks and Soper, 1987; Marchant, 1990; del Hoyo, et al., 1992).
c. Emperor penguins breed annually during the antarctic winter, June through August (Sparks and Soper, 1987).
(1) During the emperor breeding season, air temperature may drop to -60°C (-76°F) and winds may reach speeds up to 200 kph (124 mph) (del Hoyo, et al., 1992).
(2) For most of the winter, antarctic penguins live in an environment of darkness or half-light. Why emperors breed during the harshest season of the year is unknown, but some scientists speculate that when the chicks become independent five months later (in January or February, the antarctic summer), environmental conditions are more favorable for the young birds (del Hoyo, et al., 1992).
d. The fairy penguin breeds throughout the year and has the shortest breeding cycle, about 50 days (Sparks and Soper, 1987).
e. Some of the temperate penguins, like the Humboldt and the African, tend to nest throughout the year (del Hoyo, et al., 1992).
2. Courtship
a. Courtship varies among the species. It generally begins with both visual and auditory displays. In many species, males display first to establish a nest site and then to attract a mate.
b. Most penguin species are monogamous (one male breeds with one female during a mating season) (del Hoyo, et al., 1992); however, research has shown that some females may have one to three partners in one season and some males may have one or two partners (Davis and Speirs, 1990).
c. Mate selection is up to the female, and it is the females that compete for the males (Davis and Speirs, 1990).
d. A female usually selects the same male from the preceding season (Sparks and Soper, 1987). Adélie penguins have been documented re-pairing with the previous year's mate 62% of the time. Chinstraps re-paired in 82% of possible cases, and gentoos re-paired 90% of the time (Trivelpiece, 1990). In one study of Adélies, females paired with males within minutes of arriving at the colony (Davis and Speirs, 1990).
e. When a female selects a different mate it is usually because her mate from the previous season fails to return to the nesting area. Another reason may be mistiming in returning to the nesting area. If they arrive at different times and miss each other, one or the other penguin may obtain a new mate (Davis and Speirs, 1990).
C. Nesting
1. Nest site fidelity.
a. Studies have shown that most penguin species tend to be faithful to the same rookeries and return each year. Most penguins return to the same territory within the rookery (Sparks and Soper, 1987). Male Adélie penguins were 99% faithful to the previous year's territory, chinstraps were 94% faithful, and gentoos were 63% faithful (Trivelpiece, 1990).
b. Males arrive first to the rookeries to establish and defend their nesting sites. (Sparks and Soper, 1987). In a study on Adélie and chinstrap penguins, females arrived one day and five days after the males, respectively (Trivelpiece, 1990).
c. Some scientists believe that penguins build up numbers in a single rookery rather than colonize new areas because mature birds return to the rookery where they hatched when it is time to breed. Some penguin rookeries number millions of birds (Muller-Schwarze, 1984).
2. Nesting habitats vary among species (Marchant, 1990).
a. Emperor penguins form colonies around the shoreline of the antarctic continent and adjacent islands. They prefer sites on a fairly level surface of ice in areas sheltered from wind, with easy access to feeding areas (Sparks and Soper, 1987; Marchant, 1990).
b. King penguins nest and breed on subantarctic and antarctic islands. They prefer beaches and valleys of level ground or gentle slopes, free of snow and ice, and accessible to the sea (Marchant, 1990).
c. Adélies often nest 50 to 60 km (31.1-37.3 mi.) from the edge of the sea ice on the antarctic continent and nearby on rocky islands, peninsulas, beaches, hillsides, valleys, and other areas free of ice (Falla, 1937; Harrington, 1960; Johnstone, et al., 1973).
d. Gentoo penguin colonies can be inland or coastal on antarctic and subantarctic islands and peninsulas. They tend to breed on ice-free ground on beaches, in valleys, on inland hills, and on cliff tops (Murphy, 1947; Falla, 1937; Rand, 1954; Despin, 1972; White and Conroy, 1975; Robertson, 1986).
e. Chinstrap penguins nest on fairly steep slopes (del Hoyo, et al., 1992).
f. Fiordland crested penguins nest in a wet, coastal rain forest habitat, under bushes, between tree roots, in holes, or in caves (del Hoyo, et al., 1992).
g. Galapagos penguins nest in volcanic caves or cracks in rock (del Hoyo, et al., 1992).
Some penguins, like these gentoos, construct nests of small
stones.
h. The temperate penguins and the fairy penguin nest underground in burrows. These species breed in areas where the climate can range from tropical to subantarctic. Underground burrows provide an environment with a relatively constant temperature (about 25° to 29°C, or 70° to 84°F) for the eggs and chicks.
i. Humboldt penguins burrow and create nesting sites in guano (fecal) deposits (Scolaro).
3. Nesting materials vary from species to species and from location to location.
a. Adélies build nests of small stones. They are known to take stones from other Adélie nests. This stone-stealing behavior may be credited to the Adélies' nest-relieving display in which the returning penguin sometimes brings its mate a stone as a soothing gesture or greeting (Sparks and Soper, 1987).
b. Chinstrap penguins usually construct nests with perimeters of eight to ten stones, just enough to prevent eggs from rolling away (del Hoyo, et al., 1992).
c. Gentoo penguins use nesting materials ranging from pebbles and molted feathers in Antarctica to vegetation on subantarctic islands. One medium-sized gentoo nest was composed of 1,700 pebbles and 70 molled tail feathers (del Hoyo, et al., 1992).
d. Emperor and king penguins build no nests. They stand upright while incubating a single egg on the tops of their feet under a loose fold of abdominal skin. Under this loose fold is a featherless patch of skin called a broodpatch, which occurs in all incubating birds. The brood patch contains numerous blood vessels, that, when engorged with blood, transfer body heat to the eggs.
D. Eggs
1. Eggs may be white to bluish or greenish. The shape varies among species. In Humboldts and Adélies the egg is more or less round. In emperors and kings the egg is rather pear-shaped, with one end tapering almost to a point.
2. Egg size and weight varies with species. From the records of SeaWorld's successful penguin breeding programs, emperor penguin eggs measure 11. 1 to 12.7 cm (4.4-5 in.) long and weigh 345 to 515 g (1 2.1-18 oz.), and Adélie penguin eggs measure 5.5 to 8.6 cm (2.2-3.4 in.) and weigh 61 to 153.5 g (2.1-5.4 oz.).
3. A nest of eggs is called a clutch, and with the exception of emperor and king penguins, clutches usually contain two eggs. (Emperor and king penguins lay a single egg. ) A clutch with more than one egg presents a better chance of at least one chick surviving (del Hoyo, et al., 1992).
a. In the Eudyptuia, Spheniscus, and Pygoscelis genera, the first-laid egg is generally larger than the second, and usually hatches first (except in the chinstrap species) (Lamey, 1990). Usually the first chick to hatch has the survival advantage since it will already have fed and will be larger by the time the second egg hatches (del Hoyo, et al., 1992). The second, usually smaller, chick cannot compete with the larger chick for food and usually perishes (Lamey, 1990).
b. In the Eudyptes genus, the second-laid egg and subsequent chick is usually the larger of the two. The second chick usually is the survivor. Researchers have yet to find an adequate theoretical explanation for this reversed pattern (Davis and Darby, 1990).
c. The chinstrap and yellow-eyed species usually lay two eggs. Parents typically raise both chicks, which are nearly equal in size (Davis and Darby, 1990).
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