Tele prime lenses, tele zoom lenses, or ultra zoom lenses, with a reach of 400mm (full frame equivalent), or more, are "long lenses" that can generally be called favorable, for shooting still images and videos of birds and wildlife. For photographing small shy birds, 600mm (full frame equivalent), or more, is generally recommended.

If your sneaking/hiding skills are excellent, and/or your living subjects are not very wary of you, and/or if you aim for an environment/landscape/group style photo that includes living bird/wildlife subjects, you may be able get great photos using a lens with a shorter focal length. However, when capturing portraits, and/or specific natural behaviours, while trying to minimize disturbing your living subjects, "long lenses" usually provides an advantage. When photographing dangerous animals, using "long lenses" may also be safer, as it allows you to keep a longer distance from them, which is preferable, unless you are an adrenaline junkie, and/or a professional photographer, aiming for unique high risk "money shots" at a closer distance.

Focal length is not the only important aspect when choosing a long lens. You may also consider other factors, for example: Camera compatibility, price, size, apertures, sharpness, weight, weight distribution, autofocus, stabilization, chromatic aberration, weather sealing, closeup distance, sound noise, ergonomics, zoom/prime etc. Some photographers own several "long lenses" and use them, or leave them at home, according to the situation. Sometimes it may also be a good idea to rent an appropriate "long lens" for a special occasion.

Aside from long lenses that originally have a reach of 400mm (full frame equivalent), or more, it is also possible to sometimes achive above 400mm (full frame equivalent) by adding a tele converter (usually 1.4x, or 2.0x), to a slightly shorter tele lens (for example a 300mm lens), and/or using a camera that has a crop factor (usually 1.5x, 1.6x, or 2.0x), and/or has a high resolution image sensor that produce images that can be cropped, to multiply the orginal focal lenght to achieve the desired full frame equivalent focal length, to compose an image. However, long lenses with a reach of 400mm (full frame equivalent), or more, are often (but not always) also compatible with tele converters etc. If you want to use a tele converter, or not, is kind of like a balancing act, because there are both advantages and disadvanages to using a tele converter, depending on your circumstances. Occasionally, you may also want to use an extension tube, if you want to photograph subjects at close distance.

Afocal photography through a spotting scope made for bird watching, or through a telescope made for astronomy viewing, can be called digiscoping (if a digital camera is used), or phonescoping (if a smartphone is used). Digiscoping was popular during a few years, from when the concept was first introduced in 1999. Since then, technological development regarding relatively affordable long lenses, with image stabilization (both for panning and multidirectional vibration reduction), dedicated to photography and videography, has made digiscoping generally less favourable among photographers and videographers. However, digiscoping and phonescoping may still be an option depending on your circumstances.