Skeezer subsequently kept Leggy in his and Blake's makeshift home aboard an old train, believing the young Terror Bird to have escaped from a private egg farm. Skeezer named the Bird Leggy and initially fed him cheese puffs, then later kept him in a cardboard box.
When Blake and Skeezer captured Evan Cross and Dylan Weir, they showed Leggy to the two and Dylan realised that the juvenile Bird was actually Titanis walleri. After the Terror Bird incursion was dealt with, Ken Leeds secretly took Leggy and lied to the Cross Photonics team that the juvenile Terror Bird had been returned through the Anomaly with the other Birds.
Leeds subsequently handed Leeds over to the military so as to get Project Magnet reactivated, and the military raised Leggy in a government laboratory. At the lab, the personnel subjected Leggy to cruel and painful experiments. A few months after arriving at the lab, by which time Leggy had grown into an adult, the Terror Bird managed to break out of his cage when a doctor was attempting to sedate him in preparation for a rectal biopsy. Leggy then broke out via the lab's windows into Vancouver, attacking a druggy's car in a parking garage before travelling into an alley outside the garage.
Leggy was scavenging in a dumpster in the alley for food, when Evan Cross, Dylan Weir and a squad of soldiers led by Major Douglas arrived and found him. When one of the soldiers attempted to tranquilise Leggy, the Bird fled the scene and escaped. Leggy subsequently travelled to the Doug Mitchell Thunderbird Sports Arena and stalked the arena's maintenance tunnels, where he killed Corporal Turner and fed off of Human sacks he found there.
Leggy eventually left the maintenance tunnels and attacked Major Douglas' men in the arena's ice-skating area; killing Corporal Givens and injuring Douglas, before Sergeant Macready shot Leggy in the leg, which caused the Terror Bird to flee onto the ice rink. When Evan and Dylan shot Leggy with two tranquiliser darts in a failed attempt to tranquilise him, the Bird fled back into the maintenance tunnels and hid there. When Evan and Dylan found Leggy, they made a trail of cheese puffs which began to lure him. Dylan further lured Leggy out into the open with fake bird calls, and Evan then managed to shoot Leggy with a tranquiliser dart. Leggy then noticed Evan and Dylan and tried to attack, but succumbed to the tranquiliser before he could reach them. After Dylan concluded that there was no way to save Leggy from both his leg injury and the soldiers, she shot the unconscious Terror Bird in the head as a mercy killing.
As a juvenile, Leggy was shown to be curious and harmless, and had a love for Human snacks (such as cheese puffs) and marijuana. Leggy also had a love for meat such as chicken, and became slightly hostile and faster when after meat. After maturing to adulthood, Leggy became afraid of and highly aggressive and agitated towards Humans, most likely due to his brutal upbringing by Human scientists. He also lost his curious streak and became more afraid and timid when investigating something. As an adult, Leggy did retain his liking for Human snacks such as popcorn and cheese puffs, and was a scavenger rather than a hunter, but would still attack Humans on sight.