The Grimbill

Scythesnout kiwizelles were once the most numerous herbivore on the woodlouse-grassland, traveling in herds hundreds strong. They migrated into the hybrid taiga after their habitat collapsed, diverging into two groups. One abandoned grazing in favor of highly selective browsing, while the other became a dietary generalist, feeding opportunistically on every food source the forest had to offer. The former subspecies went extinct at the end of the Ice Age as the taiga shrunk and non-sweetstalk skystalks declined in diversity. The omnivores fared much better. They stalked the woods, creeping up on unsuspecting animals. Just when their prey tried to flee, they used their hooked lower bill to trip it, crippling it by severing muscles and tendons. They didn't even need to deliver a killing blow; they could simply begin tearing off strips of meat while their downed victim bled out. These hookjawed scythesnouts were to the forest what the terror kiwis were to the open plains. Today, their descendants are known as the Grimbill.

Grimbills (Ursapteryx) are the largest predator in the northern temperate zone, being found from the Ailuropian Streamlands across Ailox to the woods of Northlox. Weighing up to 100 kilograms, they are quadruple the size of their scythesnout ancestors. They still have a long, hook-like protrusion on their lower jaw, though the beak overall is deeper and stronger than it once was. The upper bill has two smaller tooth-shaped edges that aid in processing food, but the lower hook is the primary weapon. The grimbill's resting posture is upright, with its heavy head balanced over its body. When running, it switches to a more horizontal position, holding its head low to the ground as it closes in to strike at its target's legs. 

Hunting is not always a solitary endeavor; mated pairs may work together to take on large, swift prey. They keep an eye on the woodland herd-birds that make up a large fraction of their diet. The couple waits for the herbivores to pass through a small ravine, the bottom of a cliff face, or some other natural choke point. One of them (usually the smaller and faster of the two) positions itself in a hidden location ahead of the herd, while the other approaches from behind. The large partner jumps into view of its target, spooking it and causing it to flee in the other direction. With only one way to run, the herd-bird passes by the hidden predator, which leaps out from the darkness to land a bite on its leg. 

Once a year, the two will incubate their egg in a large nest hidden in vegetation. They often form short-term groups of three to five couples during this period, scaring egg thieves away from each other's developing offspring. The young only receive a week or two of care, being fed by all members of the temporary colony. They'll be taught a few hunting skills, shown which of the forest's plants are poisonous and must be avoided, and guided around the local territory in this brief window, but their most important lesson is one their parents cannot teach them. The chicks will have to form a pack to survive their long and dangerous childhood, learning each member's strengths and weaknesses so they can operate as a group. 

Once they leave the safety of the breeding colony, they must hunt and forage with no assistance. Though their adult diet will be an even split between meat and plant matter, at this stage they need much more protein. Starting with small rats, fish, and groundfowl, they learn what strategies are best for each. As they grow, they begin to seek out bigger game. Like their parents, they work together to bring down raspbirds and other kiwizelles. This is the stage when every individual figures out which role it's better at, with some pack members taking on the "chaser" position and others becoming "strikers". 

Soon, the young grimbills begin feeling the inescapable urge to seek out a lifelong mate. The pack disperses without violence, and all members go their separate ways. Each of them will travel long distances to find others of its species. Whenever two prospective partners meet, they go hunting together to gauge each other's skills. The success or failure of the hunt informs them of whether they'll make an effective team. If they don't catch anything, they both continue their search, but if they succeed they'll remain together for life. This instinct to choose a mate on the basis of prey-killing compatibility sometimes leads to partnerships between two grimbills of the same sex who have complimentary hunting roles.