Giant Seawis of Perinesia

Perinesia is Apterra's largest submerged landmass, composed of a continental plate that mostly rests just a few hundred meters below sea level. Located south of Sub-Abeli, some two dozen small and mid-sized islands poke out above the waves. These lands are fertile, temperate, and isolated, with no major terrestrial predators. The wide channels between them are equally productive, as enough light reaches the seabed to support a massive meadow of plumekelp. Teeming shoals of fish can number in the billions, while Caenarthrids and sludgescuttlers creep across the sand. Grumblefish wait for the opportunity to ambush their prey, hiding in the algae until they get the chance to strike. Plumekelp provides little cover for any species bigger than about 30 centimeters, so larger predators need a different strategy.

The Perinesian Oarbird (Orcinapteryx perinesiensis) is the largest seawi - indeed, the largest bird - yet to evolve on Apterra, reaching 750 kilograms in mass. It's a powerful swimmer, with enormous paddle-like legs to propel it up to 30 kilometers per hour. Since it can't hide on the seabed, it swims just below the waves as it searches for fish. Because it attacks from above, it runs the risk of giving itself away too soon by casting a shadow on its targets. To prevent this, it hunts at dusk and dawn, approaching shoals from the west in the morning and from the east in the evening. Its fifty-centimeter bill has a flat, diamond-shaped cross-section, allowing it to sweep side-to-side easily in the water. Using this method, an oarbird can catch twenty fish per minute, darting repeatedly in and out of a baitball until it's had its fill. 

Males are about triple the size of females, who still have to haul themselves onto the beach to lay their eggs. Even the smaller sex is extremely clumsy on land, as they can't stand upright and must push themselves across the sand. A single 1500-gram egg is laid in a nest dug into the ground, hatching in 29-32 days. With no natural threats on the islands, little post-birth care is needed - the chick simply scurries off into the vegetation and lives on the island until around its first birthday, when it reaches about a third of its adult size and gains the toe webbing that allows it to swim. Meanwhile, the mother returns to greet her mate, who's spent the last few weeks bulking up. He regurgitates food for her many times to help her regain her strength, for she's spent the entire nesting period fasting. With his help, she's back to full health in about two months. The two then immediately mate again, and she may hatch three or four chicks each year. 

Though oarbirds generally hunt alone or in pairs, they occasionally form pods of up to 15 for protection. Giant stoutlings are their only major threat, especially to females and the young. Since stoutlings only migrate through Perinesia in mid-winter, these pods are temporary, and established couples break away to reclaim their territories once the danger passes. For the adolescents, though, these short-term social gatherings provide a chance to find a permanent mate. If there are relatively few young females around, males may spar in dramatic battles at the surface, clattering their beaks together above the waves. Though neither aims to draw blood, the fights occasionally result in one of the rivals snapping his upper bill, an injury that almost always proves deadly because it renders him unable to catch food. Most of the time, though, there is a peaceful resolution, and if subadult females outnumber males there is often no need to compete at all. Sooner or later, nearly every individual that survives childhood finds a partner to spend the rest of its fifty-year lifespan with.