Penguins sleep in more than one way. They may rest standing, lying down, or near a nest or burrow. Nesting chinstrap penguins have also been recorded splitting sleep into many seconds-long microsleeps.
Fast ice is sea ice fixed to coasts, ice walls, ice-shelf fronts, shoals, or grounded icebergs; for emperor penguins, it can be the floor that breeding, chicks, and moult depend on.
Penguins are often seasonally monogamous, not always mates for life. King, emperor, and little penguin divorce patterns turn on timing, nests, and failed breeding.
Many penguin parents raise young in shifts: one guards the egg or chick while the other goes to sea for food. They keep chicks warm, regurgitate meals, and in some species use creches as chicks grow.
Penguin courtship begins with posture, calls, and stones, but the real test comes in incubation shifts and chick-rearing; under the romantic surface is a cooperative system that cannot afford mistakes.
A decade of data from the University of Oxford and Oxford Brookes University shows Antarctic gentoo penguins breeding 13 days earlier per decade on average, with some colonies shifting by 24 days.