The New Zealand falcon is a sedentary bird that spends most of its time within or close to its home range. The home range of a falcon varies, with calculations from 200 km2 to 15 km2, with dependence on food availability. Observations of captive falcons stooping rabbits and a cat were noted as playful or territorial rather than for hunting purposes. The most common avian prey includes introduced
finch,
lark,
pipit, and
thrush species,
silvereyes,
blackbirds, and the
yellowhammer. Other avian prey include other
passerines,
waterfowl,
seabirds (e.g.,
gulls), domestic
poultry and
gamebirds (e.g.,
ring-necked pheasants),
parakeets,
pigeons, and even
herons. The falcon is adept at capturing introduced birds, with their make up in the prey composition being slightly higher than their proportional abundance. They also hunt
skinks and hard-bodied insects like
beetles,
locusts,
cicadas, and
dragonflies. It also occasionally takes advantage of
carrion (including
fish) to get a quick meal. One was recorded feeding on the fruits of
Styphelia nesophila. As the prey composition is closely related to the local species abundance, studies on the diet of the three forms come with slightly different results. The eastern falcon is recorded with a higher proportion of mammalian prey than the bush falcon. The southern falcon hunts forest birds as well as seabirds when they come in at dusk, and one was recorded eating a
little blue penguin. The New Zealand falcon has little competition for food as there are no native mammalian predators, and 2 other native birds of prey are nocturnal. They do compete with the swamp harrier, which searches for prey while flying. The competition reduces over winter when the swamp harrier relies more on carrion that the falcon does not eat. or during midday summer heats when the falcon is lethargic. Intact seeds have been recorded in New Zealand falcon pellets previously, and were attributed to secondary consumption from eaten frugivorous birds, but there has been one observation of a falcon directly consuming an orange alpine fleshy fruit from
Leucopogon fraseri. The faecal sac was examined and found to have intact seeds from that plant and another species,
Gaultheria depressa. Captive falcons have also been observed to eat fruit given to them. The New Zealand falcon tends to stay in the same pair and breeding territory each breeding season. The distance between pairs varies from . Artificial nesting sites have been provided in vineyards for the New Zealand falcon as a pest control and conservation programme. In native podocarp forests bush falcons nest in
epiphytes, tree cavities, and snags on mature trees, but will nest on a sheltered ground spot when these are absent. The ovoid eggs vary in colour, but are usually pale to very dark pink when first laid, and are around . Recorded deaths are mostly from electrocution, but also include other man-made hazards such as introduced cats, road hazards, shooting, poison, and window strike. Juvenile falcons make up a large proportion of these deaths. Falcons are also killed by swamp harriers, but these deaths are not recorded in proportion to their occurrence. ==Relationship with humans==