Hihi are generally regarded as seasonally territorial where males will aggressively defend distinct areas during the breeding season. Sometimes these areas are occupied by these same males year round, however with less exclusivity. Female hihi initiate nest building from late September and in a typical season – on Tiritiri Matangi Island at least – approximately half of these females will attempt a second clutch.
Hihi are a cavity nesting species with a clutch size of between 3 – 5 small white eggs. Cavities are usually located high up live mature trees of a variety of native species. They also readily use artificial nest boxes when mature trees with cavities are limited. Females take sole responsibility for incubation and do so for about 14 days before hatching. Nestlings are then cared for by both the female and male, although it's the female who does most of the work. Hatching success is generally low in this species and even when the majority of eggs hatch the survival of all nestlings is unlikely. The nestlings grow in the nest for about 30 days before fledging and then remain dependant on their parents as fledglings for a few weeks.
The hihi mating system is extreme to say the least. The best way to describe them is that they are highly promiscuous with intense competition for breeding opportunities. This includes often large groups of male birds moving between the territories of fertile females and forcing copulations on them. In addition to targeting fertile females they are sometimes recorded conducting similar behaviours to non–fertile females and even recently fledged juvenile birds. Although the majority of hihi attempt to breed as socially monogamous pairs in this environment, there are variations on this theme with frequent evidence of polygyny, polyandry and polygynandry. The socially paired male will also engage in a mixed reproductive strategy he becomes an extra–pair male at other nests once his own female is no longer fertile.
Perhaps their most unusual behaviour though is that hihi copulate in two positions. Along with the normal Passeriformes style, hihi perform face–to–face copulations. This appears to be unique in the bird world. These face–to–face copulations are forced by the male and resisted by females. Most often they occur between extra-pair males and socially paired females, but not exclusively so, as social mates will also perform such behaviour. Its no surprise therefore that extra-pair paternity is high and common across nests.
Text by: John G Ewen & Rose Thorogood