<P> Emperor penguins are serially monogamous . They have only one mate each year, and stay faithful to that mate . However, fidelity between years is only about 15% . The narrow window of opportunity available for mating appears to be an influence, as there is a priority to mate and breed which often precludes waiting for the appearance of the previous year's partner . </P> <P> The female penguin lays one 460--470 g (1.01--1.04 lb) egg in May or early June; it is vaguely pear - shaped, pale greenish - white, and measures around 12 cm × 8 cm (4 ⁄ in × 3 ⁄ in). It represents just 2.3% of its mother's body weight, making it one of the smallest eggs relative to the maternal weight in any bird species . 15.7% of the weight of an emperor penguin egg is shell; like those of other penguin species, the shell is relatively thick, which minimizes risk of breakage . </P> <P> After laying, the mother's nutritional reserves are exhausted and she very carefully transfers the egg to the male, before immediately returning to the sea for two months to feed . The transfer of the egg can be awkward and difficult, and many couples drop the egg in the process . When this happens, the chick inside is quickly lost, as the egg cannot withstand the freezing temperatures on the icy ground . The male spends the dark winter incubating the egg in his brood pouch, balancing it on the tops of his feet, for 64 consecutive days until hatching . The emperor penguin is the only species where this behaviour is observed; in all other penguin species both parents take shifts incubating . By the time the egg hatches, the male will have fasted for around 115 days since arriving at the colony . To survive the cold and winds of up to 200 km / h (120 mph), the males huddle together, taking turns in the middle of the huddle . They have also been observed with their backs to the wind to conserve body heat . In the four months of travel, courtship, and incubation, the male may lose as much as 20 kg (44 lb), from a total mass of 38 to 18 kg (84 to 40 lb). </P> <P> Hatching may take as long as two or three days to complete, as the shell of the egg is thick . Newly hatched chicks are semi-altricial, covered with only a thin layer of down and entirely dependent on their parents for food and warmth . If the chick hatches before the mother's return, the father feeds it a curd - like substance composed of 59% protein and 28% lipid, which is produced by a gland in his oesophagus . This ability to produce "milk" in birds is only found in pigeons, flamingos and male Emperor penguins . The young chick is brooded in what is called the guard phase, spending time balanced on its parent's feet and sheltered in the brood pouch . </P>

Where do female emperor penguins go in the winter