The Hoopoe is a medium sized bird, 25–32 cm (9.8-12.6 in) long, with a 44–48 cm (17.3-19 in) wingspan weighing 46-89 g (1.6-3.1 oz). The species is highly distinctive, with a long, thin tapering bill that is black with a fawn base. The strengthened musculature of the head allows the bill to be opened when probing inside the soil. The hoopoe has broad and rounded wings capable of strong flight; these are larger in the northern migratory subspecies. The Hoopoe has a characteristic undulating flight, which is like that of a giant butterfly, caused by the wings half closing at the end of each beat or short sequence of beats.
The song is a trisyllabic "oop-oop-oop", which gives rise to its English and scientific names.
In what was long thought to be a defensive posture, Hoopoes sunbathe by spreading out their wings and tail low against the ground and tilting their head up; they often fold their wings and preen halfway through. The Hoopoe also enjoys taking dust and sand baths.
 Diet and feeding
The diet of the Hoopoe is mostly composed of insects, although small reptiles as well as some plant matter such as seeds and berries are sometimes taken as well. It is a solitary forager which typically feeds on the ground. More rarely they will feed in the air, in pursuit of numerous swarming insects, where their strong and rounded wings make them fast and manoeuvrable. More commonly their foraging style is to stride on relatively open ground and periodically pause to probe the ground with the full length of their bill. Insect larvae, pupae and mole crickets are detected by the bill and either extracted or dug out with the strong feet. In addition to feeding in soil Hoopoes will feed on insects on the surface, as well as probing into piles of leaves and even using the bill to lever large stones and flake off bark. Common diet items include crickets, locusts, beetles, earwigs, cicadas, ant lions, bugs and ants. These can range from 10 to 150 mm in length, with the preferred size of prey being around 20-30 mm. Larger prey items are beaten against the ground or a preferred stone in order to kill them and remove indigestible body parts such as wings and legs.
The Hoopoe is monogamous, although the pair bond apparently only lasts for a single season. They are also territorial, with the male calling frequently to advertise his ownership of the territory. Chases and fights between rival males (and sometimes females) are common and can be brutal. Birds will try to stab rivals with their bills, and individuals are occasionally blinded in fights. The nest is in a hole in a tree or wall, with a narrow entrance; it may be unlined or various scraps may be collected. The female alone is responsible for incubating the eggs. Clutch size varies with location, with northern hemisphere birds laying more eggs than those in the southern hemisphere and birds in higher latitudes having larger clutches than those closer to the equator. In central and northern Europe and Asia the clutch size is around 12, whereas it is between four in the tropics and seven in the subtropics. The eggs are round and milky blue on laying but quickly discolour in the increasingly dirty nest. They weigh 4.5 grams. A replacement clutch is possible.
The Hoopes have well developed anti-predators defences in the nest. The uropygial gland of the incubating and brooding female is quickly modified to produce a foul-smelling liquid, and the glands of nestlings do so was well. These secretions are rubbed into the plumage. The secretion, which smells like rotting meat, is thought to help deter predators, as well as deter parasites and possibly act as an antibacterial agent. The secretions stop soon before the young leave the nest. In addition to this secretion nestlings are able to direct streams of faeces at nest intruders from the age of six days, and will also hiss at intruders in a snake like fashion. The young also strike with their bill or with one wing.
The incubation period for the species is between 15 and 18 days. During incubation the female is fed by the male. The incubation period begins as soon as the first egg is laid, so the chicks are born asynchronously. The chicks hatch with a covering of downy feathers, by around day days feather quills emerge which become adult feathers. The chicks are brooded by the female for between 9 to 14 days. The female later joins the male in the task of bringing food. The young leave the nest after approximately three and a half weeks; the parent still leads them for a week.