Meeting Abstract

98.3  Saturday, Jan. 7  Free-flight dynamics of peregrine and pigeon – predator and prey. USHERWOOD, JR; The Royal Veterinary College

Newly developed GPS and inertial loggers record high rate and quality in a small package. This allows direct measurements of free flight and flock dynamics in birds down to the size of pigeons. Findings from a flock of 18 racing pigeons, and from a male and female peregrine, demonstrate contrasting aerodynamic strategies between predator and prey. FAST-FLYING pigeons make flapping turns at up to 2g, banking, yawing and pitching consistent with aerodynamic optimality. In response to the resulting increase in effective weight, they increase flap frequency (from 7 to 9Hz) but reduce flap amplitude (from 1cm down to 0.5cm). This is not expected from purely muscle power considerations, and indicates a shifting compromise between flapping with high aerodynamic efficiency (high frequency, low amplitude) and low inertial power (low frequency). When flying near neighboring birds, pigeons increase flap rate (by around 0.1Hz), suggesting an energetic cost to flying within a flock. PEREGRINES are well known for their speed. However, they appear incapable of prolonged ascending flight in still air, and are largely reliant on harvesting energy from the environment. In the cases studied here, this consisted of either slope-soaring or being carried by the handler up a 42m tower. Vertical stoops initiated from the top of the tower began with flapping downward acceleration, and a non-flapping pull-out at 5g; maximum speeds for these stoops only got up to 22m/s – achievable in level flight by racing pigeons. However, peregrines can use height as an effective energy store: free-fall increases kinetic energy at 50 W/kg – a rate close to the maximum for a pigeon powering flight directly through muscles – after only 0.5s, or 1.25m. THE SUCCESS of peregrines as predators of pigeons may thus be attributed to aerodynamic cunning during ascent, and gravity-powered acceleration during descent. Racing pigeons are, however, very much more impressive athletes.