Ringed seals maintain breathing holes through landfast ice using the heavy claws on their fore-flippers. Where snow drifts deeply over a hole, typically along pressure ridges, the female hollows out a chamber above the water and bears a single pup in it. The lair is invisible from the surface.
The insulation matters. Inside the lair the pup is out of the wind and shielded from a concealed approach by predators, and it is nursed for around five to seven weeks, longer than most ice-breeding seals. Polar bears hunt largely by locating these lairs by scent and crashing through the roof.
The arrangement depends on two things arriving together: enough stable landfast ice and enough snow on it. Rain-on-snow events and early break-up can collapse or expose lairs, and this dependency is the main reason the Arctic ringed seal subspecies is listed as threatened under the US Endangered Species Act despite a global population in the millions. How rapidly that risk translates into population decline is not yet measurable.