Draw inspiration from the work of artists whose specialty is birds. John James Audubon, famous for his lush depictions of hundreds of bird species, is an obvious choice. His vibrant use of color, intriguing settings and stylistic exaggerations are an education in and of themselves. Bird art has made a significant contribution to our scientific understanding of avian species as seen by the efforts of the British master George Edwards. Rembrandt and Da Vinci also enjoyed painting birds.
Birds are a portrait in constant movement; trying to depict them authentically, regardless of your chosen medium, requires a highly specialized skill set. While photography is a good resource for artists, it's no substitute for bird-watching. If you build a bird feeder, they will come! For more ambitious fieldwork, the Internet offers instruction in how to build a blind, which allows you to watch, undetected, birds in their natural habitats. It wasn't uncommon for Audubon and his peers to kill birds and then pose and paint them; presumably, you won't find that kind of dedication either necessary or desirable.
The Internet is a gift to aspiring artists. There are online classes devoted to drawing and painting birds, many of them free of charge, as well as tutorials featuring videotaped instruction. There any number of excellent books on the subject of birds in art, both instructive and inspiring. If you prefer real-world instruction, your local arts center is a good starting point for specialized classes and workshops. Many artists offer one-on-one instruction.
The medium in which you choose to paint is as critical as the subject matter. Since sketching is an important part of the process, begin with pencil, pen and ink, pastels or charcoal, which generally demand less expertise than oil, watercolor or acrylics. Consider the many subsets within those broader categories: Chinese brush art, for instance, renowned for its delicacy, emphasis on design and subtlety. At the same time, inform yourself as to the accepted conventions of bird art. For example, birds are generally painted relative to their actual size, for authenticity's sake.