Honey buzzards return from their wintering grounds in equatorial Africa in mid-May. The breeding season is timed to coincide with abundance of wasp larvae, which is the principal food of nestlings.
The home range tends to be large (mostly c.10km², but up to 40km²), and often overlaps with neighbouring pairs. The size of the home range is determined at least in part by food availability in the environs of the nest. The area immediately around the nest is defended against all other birds of prey.
The nest is on a branch of a large tree, usually 10-20 m above ground. A new nest is normally built, but old nests of crow, common buzzard etc are sometimes used.
The main bulk of the nest is made up of twigs, but the upper part at least is made up of live material with green leaves, making the nest appear as a mass of greenery. Sprays of green are added throughout the nesting period to maintain green appearance. Nest building is done mainly by the female, with a new nest completed in 10-15 days.
A clutch of two white eggs, heavily marked with deep purple-red blotches are laid at 3-5 day intervals in May. Incubation starts with the first egg, and takes up to 37 days - 30-35 days per egg. Both sexes incubate, but the female takes a greater share, and probably all of the night shifts.
The eggs hatch a few days apart, but unlike in most birds of prey there is no aggression between the siblings, and there is usually little competition for food. The female broods the young almost continuously for the first 7-10 days. From 18 days the young are able to feed themselves from food in the nest, and then both parents bring food and deposit it in the nest.
The male helps to brood the young and feeds them directly even in the presence of the female. If the female is lost, the male is able to successfully rear the brood alone. The young fledge at 40-44 days, and return to the nest for food until about 55 days old. They are independent from 75-100 days. Only one brood a year is raised. Replacement clutches after egg loss are possible but rare. Age of first breeding is not known.
Autumn migration takes place in September.
Estimates of population and trends are difficult because of the secretive habits of the species. Natural population fluctuations occur, but overall the population is stable through most of Europe.
There are some indications of past declines in Sweden and current declines in the Finnish and German populations, while the French population is slowly increasing. The honey buzzard was not affected by the pesticide-related declines that affected most birds of prey in the 1950s and 1960s, presumably because its food-chain was less contaminated.