Exploring Everyday Things with R and Ruby

Colophon

The animal on the cover of Exploring Everyday Things with R and Ruby is the hooded seal (Cystophora cristata), a finned mammal native to the North Atlantic Ocean. Its scientific name is Greek for “bladder-bearer,” so named for the large inflatable hood that develops on the head of the males when they are around four years old. This hood is used for courtship, as well as to intimidate rivals and enemies—hooded seals are one of the most aggressive seal species. When deflated, the bladder hangs down the forehead and between the eyes. Males also have a red secondary sac inside one nostril, which they can inflate by closing their other nostril valve.

Females are not as distinctive (or as large): they are around 7 feet long and 440 pounds, while males average 8 feet long and 660 pounds. However, both sexes have silvery fur with dark irregular spots. As with other semi-aquatic mammals, they have sleek clawed flippers that efficiently move them through water, but are clumsier on land.

Hooded seals are highly migratory, and will travel long distances throughout the year for food (generally by themselves), only to regroup at breeding grounds in late winter to mate and in summer to molt. They hunt in the water, able to dive almost 2,000 feet and stay underwater nearly an hour. Their diet changes depending on their location, but generally consists of fish, squid, shrimp, octopus, and mussels.

In their first 14 months, hooded seal pups have a blue-grey coat and pale bellies, giving them ...