Ed Gernon rescued a feral dog that he named 'Rex'. He understands that Rex is a "wild" dog and grew up very independent and used to his rough ways. But he was surprised when Rex saved a dying humming bird. Maybe the thought of Rex doing something so caring towards other animals is improbable because he lived a tough life saving his own life.
He decided to take in and nurse the hummingbird until well. Eventually, the hummingbird became a part of his family and they now simply call her 'Hummer'.
It's also no surprise that Hummer developed a cute and amusing bond with Rex for having saved her life. This just goes to show that animals can also feel empathy and gratitude for other creatures.