Songbird

"Songbirds. They are the pride of Columbia. When I kill them, I would make them poultry, like when I eat chicken. If I kill every songbird, then Columbia would be much safer without them. My village is very afraid of Songbirds. If they come to my village, they would kill people and destroy buildings. I cannot let them invade there."

--Su Ji-Hoon, The Songbirds

A Songbird is a creature or construct of undetermined origins that is feared by the citizens of Columbia, and is Elizabeth's guardian. It is an influential character in BioShock Infinite, and also, in When the Cold Breeze Blows Away.

Design
"Songbird, Songbird, see him fly, drop the children from the sky. When the young ones misbehave,  escorts children to their grave. Never back-talk, never lie,  or he'll drop you from the sky!”

--Annie, Drunken Shanties

A Voxophone recording, along with blueprints found at Fink Factory, show that Songbird was created by Fink Industries. As with most of Fink's technology, it was based on designs discovered through a Tear. The blueprints were described as showing "a merger of machine and man, that was the lesser of man yet the greater of both parties". In reality, Fink managed to gain the design blueprints for the Big Daddy. Collaborating with Yi Suchong of Rapture, experiments were made to create the beast. At first, multiple experiments were done with animals, such as gorillas and dogs, to create a successful psychological pairbond with Elizabeth. In the end, a crude prototype was assembled, connected to a breather. Attempts to psychologically indoctrinate the prototype were not enough, so Fink and his men left it abandoned in his old laboratory. In the end, the bond between Songbird and Elizabeth was established by a freak accident -- Songbird escaped the laboratory and accidentally crashed into Elizabeth's tower, forcing Elizabeth to repair its breather. This created a successful pairbond between the beast and Elizabeth, and it would protect her fiercely. On the other hand, Suchong erroneously believed that DNA — in particular, a hair sample, was the cause of the pairbond, and attempted multiple times to figure out how to replicate the Songbird's pairbond with his own Big Daddies.

Songbird's mechanical features are similar to that of the Big Daddy, with color-changing eyes to indicate its mood. Green eyes indicate friendliness toward a person or object of focus, most namely Elizabeth; orange indicates awareness but indifference to Songbird's surroundings; and red represents heavy hostility, chiefly toward Booker. Songbird's only weapons are the metal talons mounted on its feet and knuckles, but its immense size, strength and speed allow it to effortlessly obliterate people, vehicles, and even structures.

History
When Elizabeth was imprisoned in Columbia, Songbird was created for the sole purpose of keeping her imprisoned within her Tower, and became the most feared creature in the city. During that time, it was Elizabeth's only company, bringing her such things as books, food and drinks. Although it held her captive, the creature was her caretaker and protector. As a child, Elizabeth viewed Songbird as a friend, but later came to hate it for keeping her imprisoned. When she escapes, Songbird is intent on bringing her back, even if it means destroying anyone and anything near her, including Booker DeWitt and even the Tower that she's kept in. Its name derives from the tune that plays on a steam calliope organ in Elizabeth's room in the Tower on Monument Island whenever Songbird arrives.

Bioshock Infinite
A songbird begins pursuing Booker and Elizabeth the moment she escapes from her room, destroying a huge portion of her tower in the process. Though it is capable of sundering entire portions of Columbia by ramming into them and emerging unscathed, it has one weakness: pressure. Designed for low-pressure environments, submersion in a few fathoms of water critically injures it in a short span of time. This weakness allows Booker to escape from Songbird once he falls into the waters of Battleship Bay.