Vision:

Large eyes: acute vision
Good color vision (red - ultraviolet)

Position of eyes on head:

• typically a tradeoff between how far they can see around their head (needed for predator avoidance) and how much binocular vision they have (needed to judge distance; important for predators)
• owls: eyes focus forwards, more binocular vision (better depth perception), less visual field
• woodcock: eyes can see far back around head - better predator detection, high visual field.
• bitterns: eyes can see on both sides of head: large visual field.  Retina (where nerve cells are) has two centers of good focus instead of the typical 1; allows binocular vision forward as well as large visual field

• ability to detect motion extremely high:
• can detect movement in very slowly moving objects (15°/hour); may be related to migration: ability to detect movement of sun, stars to use as compass
• can detect very rapid changes from dark to light; probably related to flight - detecting rapid changes so they don't crash

• acuity (range of frequency (pitch) and amplitude (loudness) that can be detected): most species similar to most mammals
• exception: owls can detect low power (i.e. very quiet) sounds
• exception: some pigeons can detect exceptionally low frequency sounds
• birds can detect exceptionally rapid changes in frequency
• owls: can detect direction of sound extremely accurately: ear openings at different levels, facial disk feathers focus sound

• occurs in oilbird (Caprimulgiformes) and swiftlets (Apodiformes)
• unlike bats (the best echolocators), birds use relatively low frequency sounds to echolocate
• low frequency sounds should result in less ability to detect details through echolocation
• however, swiftlets nest & roost in in huge colonies in completely dark caves and can find their way back to their nest without crashing into each other using echolocation, so it seems pretty effective

• poorly developed in most birds
• development of sense of smell extremely variable among species:
• well developed:kiwis (Apterygiformes) -- nocturnal ground feeders; nostrils at tip of bill; turkey vultures (in Ciconiiformes) -- carrion feeders; locate by smell; honeyguides (in Piciformes)  -- can locate wax by smell; Procellariiformes  -- locate nests by smell
• moderately developed: some Columbiformes, Galliformes, Falconiformes
• poorly developed: Passeriformes; rarely respond to odors but do have some sense of smell