Attack behaviour in naive Gyrfalcons is modelled by the same guidance law as in Peregrines, but at a lower guidance gain

The aerial hunting behaviours of birds are strongly influenced by flight
morphology and ecology, but little is known of how this relates to the
behavioural algorithms guiding flight. Here we use GPS loggers to record
the attack trajectories of captive-bred Gyrfalcons (Falco rusticolus)
during their maiden flights against robotic aerial targets, which we
compare to existing flight data from Peregrines (Falco peregrinus). The
attack trajectories of both species are well modelled by a proportional
navigation (PN) guidance law, which commands turning in proportion to the
angular rate of the line-of-sight to target, at a guidance gain N.
However, naïve Gyrfalcons operate at significantly lower values of
N than Peregrines, producing slower turning and a longer path to
intercept. Gyrfalcons are less manoeuvrable than Peregrines, but physical
constraint is insufficient to explain the lower values of N we
found, which may reflect either the inexperience of the individual birds
or ecological adaptation at the species level. For example, low values of
N promote the tail-chasing behaviour that is typical of wild
Gyrfalcons and which apparently serves to tire their prey in a prolonged
high-speed pursuit. Likewise, during close pursuit of typical fast evasive
prey, PN will be less prone to being thrown off by erratic target
manoeuvres at low guidance gain. The fact that low-gain PN successfully
models the maiden attack flights of Gyrfalcons suggests that this
behavioural algorithm is embedded in a guidance pathway ancestral to the
clade containing Gyrfalcons and Peregrines, though perhaps with much
deeper evolutionary origins.