Obstacle avoidance in aerial pursuit.

Pursuing prey through clutter is a complex and risky activity requiring integration of guidance subsystems for obstacle avoidance and target pursuit. The unobstructed pursuit trajectories of Harris' hawks Parabuteo unicinctus are well modeled by a mixed guidance law feeding back target deviation angle and line-of-sight rate. Here we ask how their pursuit behavior is modified in response to obstacles, using high-speed motion capture to reconstruct flight trajectories recorded during obstructed pursuit of maneuvering targets.

Visual versus visual-inertial guidance in hawks pursuing terrestrial targets.

The aerial interception behaviour of falcons is well modelled by a guidance law called proportional navigation, which commands steering at a rate proportional to the angular rate of the line-of-sight from predator to prey. Because the line-of-sight rate is defined in an inertial frame of reference, proportional navigation must be implemented using visual-inertial sensor fusion. By contrast, the aerial pursuit behaviour of hawks chasing terrestrial targets is better modelled by a mixed guidance law combining information on the line-of-sight rate with information on the deviation angle between the attacker's velocity and the line-of-sight.

Raptors avoid the confusion effect by targeting fixed points in dense aerial prey aggregations.

Collective behaviours are widely assumed to confuse predators, but empirical support for a confusion effect is often lacking, and its importance must depend on the predator's targeting mechanism. Here we show that Swainson's Hawks Buteo swainsoni and other raptors attacking swarming Mexican Free-tailed Bats Tadarida brasiliensis steer by turning towards a fixed point in space within the swarm, rather than by using closed-loop pursuit of any one individual. Any prey with which the predator is on a collision course will appear to remain on a constant bearing, so target selection emerges naturally from the geometry of a collision.

Optimization of avian perching manoeuvres.

Perching at speed is among the most demanding flight behaviours that birds perform and is beyond the capability of most autonomous vehicles. Smaller birds may touch down by hovering, but larger birds typically swoop up to perch-presumably because the adverse scaling of their power margin prohibits hovering and because swooping upwards transfers kinetic to potential energy before collision. Perching demands precise control of velocity and pose, particularly in larger birds for which scale effects make collisions especially hazardous.

Aerial attack strategies of hawks hunting bats, and the adaptive benefits of swarming.

Aggregation can reduce an individual's predation risk, by decreasing predator hunting efficiency or displacing predation onto others. Here, we explore how the behaviors of predator and prey influence catch success and predation risk in Swainson's hawks attacking swarming Brazilian free-tailed bats on emergence. Lone bats including stragglers have a high relative risk of predation, representing ~5% of the catch but ~0.

Attack behaviour in naive gyrfalcons is modelled by the same guidance law as in peregrine falcons, 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 used GPS loggers to record the attack trajectories of captive-bred gyrfalcons () during their maiden flights against robotic aerial targets, which we compared with existing flight data from peregrine falcons (). The attack trajectories of both species were 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 However, naive gyrfalcons operate at significantly lower values of than peregrine falcons, producing slower turning and a longer path to intercept.

Hawks steer attacks using a guidance system tuned for close pursuit of erratically manoeuvring targets.

Aerial predators adopt a variety of different hunting styles, with divergent flight morphologies typically adapted either to high-speed interception or manoeuvring through clutter, but how are their sensorimotor systems tuned in relation to habitat structure and prey behavior? Falcons intercept prey at high-speed using the same proportional navigation guidance law as homing missiles. This classical guidance law works well in the open, but performs sub-optimally against highly-manoeuvrable targets, and may not produce a feasible path through the cluttered environments frequented by hawks and other raptors. Here we identify the guidance law of n = 5 Harris' Hawks Parabuteo unicinctus chasing erratically manoeuvring artificial targets.

Terminal attack trajectories of peregrine falcons are described by the proportional navigation guidance law of missiles.

The ability to intercept uncooperative targets is key to many diverse flight behaviors, from courtship to predation. Previous research has looked for simple geometric rules describing the attack trajectories of animals, but the underlying feedback laws have remained obscure. Here, we use GPS loggers and onboard video cameras to study peregrine falcons, , attacking stationary targets, maneuvering targets, and live prey.

Critical role for protein kinase A in the acquisition of gregarious behavior in the desert locust.

The mechanisms that integrate genetic and environmental information to coordinate the expression of complex phenotypes are little understood. We investigated the role of two protein kinases (PKs) in the population density-dependent transition to gregarious behavior that underlies swarm formation in desert locusts: the foraging gene product, a cGMP-dependent PK (PKG) implicated in switching between alternative group-related behaviors in several animal species; and cAMP-dependent PK (PKA), a signal transduction protein with a preeminent role in different forms of learning. Solitarious locusts acquire key behavioral characters of the swarming gregarious phase within just 1 to 4 h of forced crowding.