Bird photography generally demands more focal length than most other wildlife subjects, since birds are small, easily startled, and rarely allow a close approach, which pushes the useful range up toward 400mm to 600mm or beyond for anything smaller than a large raptor.

Why Birds Need More Reach Than General Wildlife

A deer or a large mammal fills more of the frame at a given distance than a small songbird does, so focal lengths that work well for general wildlife often leave birds looking tiny in the frame. Bird photographers typically need noticeably longer glass than someone photographing larger animals from a similar distance.

Perched Birds vs Birds in Flight

A stationary, perched bird allows more time to compose and can be photographed successfully with a 400mm lens and some patience. Birds in flight are far less forgiving, since tracking a fast, unpredictable subject benefits from every bit of reach and fast autofocus a lens can offer, which is why serious bird-in-flight photographers often use 500mm to 600mm lenses or longer.

Using a Teleconverter to Extend Reach

A teleconverter can stretch a 300mm or 400mm lens into effective bird-photography range without buying a dedicated super-telephoto lens, though it typically costs some autofocus speed and light-gathering ability in exchange for the extra reach.

Crop-Sensor Cameras and Bird Photography

A crop-sensor camera effectively extends the reach of any given lens, which is part of why many dedicated bird photographers favor APS-C or Micro Four Thirds bodies paired with a shorter, lighter telephoto lens instead of carrying full-frame equivalent glass.