Songbird

"It's a Songbird. It's a constructed creature that truly is the pride of the Columbian nation. When I kill that stupid flying bird, then I would make them poultry, just like when I eat chicken, back home in my village. If I kill each of every of that Songbird, then Columbia would be much better and safer without them. Well, my village is very afraid of Songbirds, after they heard of me about them. So, if they come to my village, then they would go kill its people and destroy its buildings, and yet right now, I cannot let them invade there."

--Su Ji-Hoon, Welcome to Columbia

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.

While inside an elevator on their way to the Hall of Heroes, Elizabeth explains and demonstrates her ability to control tears by opening one to a windowsill. However, the Songbird of the Columbia she opened the tear to emerges out on the other side of the window. Before it can attack, though, Elizabeth closes the tear, revealing a propaganda poster of the Songbird in its place.

Once Booker and Elizabeth finally reach their airship, The First Lady, after the revolt at Fink Manufacturing, they begin to fly out of Columbia. Suddenly, a statue on the ship calls Songbird by playing a specific tune built into it. Songbird flies by the airship as Booker and Elizabeth frantically try to make it go faster. Songbird then attacks it and destroys it, causing them to crash land in the streets of Emporia at Port Prosperity.

At the end of Grand Central Depot, Elizabeth and Booker look for a code to unlock an elevator. Yet another statue plays the tune, which alerts Songbird to their location, and they barely escape detection. Elizabeth is shaken and dismayed by the encounter, and to console her, Booker assures her he will stop Songbird. Elizabeth responds that he can't possibly defeat the creature, and that if it came down to it, she would rather make Booker kill her than let Songbird take her back.

As Booker and Elizabeth pass the gate into Comstock House and head for the bridge, Songbird launches a surprise attack, flying from below and pinning Booker. It then grabs and throws Booker through a nearby building, quickly tearing its way inside to finish him off. Before Songbird can do so, however, Elizabeth yells out an apology, begging Songbird to take her back to the tower and spare Booker's life. Appeased, Songbird carries Elizabeth to Comstock House, where she is indoctrinated over the course of several years.

Songbird is not encountered again until Booker and Elizabeth take over Comstock's airship, The Hand of the Prophet. Through a note written by her future self, Elizabeth realizes she can control Songbird by playing the notes C, A, G, E to it on a device called the Whistler, found in every Songbird Defense System statue. She and Booker use Songbird to defend against a Vox Populi attack on the airship, then to destroy the Siphon which had been limiting her powers.