How do different animals sleep, and do some never sleep at all?

The answer

Sleep patterns across the animal kingdom are extraordinarily diverse. Dolphins and whales practice unihemispheric sleep - resting one brain hemisphere while the other stays alert, allowing them to continue surfacing to breathe. Frigatebirds sleep in 10-second bursts while soaring, totaling just 42 minutes per day during multi-day ocean flights, as documented by a 2016 study using EEG loggers. Giraffes sleep only 30 minutes daily in brief 5-minute intervals. Koalas sleep 22 hours per day to conserve energy while digesting toxic eucalyptus. Bullfrogs show no measurable sleep, though they enter restful states. Alpine swifts stay airborne for 200 consecutive days, presumably napping mid-flight using unihemispheric sleep like marine mammals.