Data from: Birds invest wingbeats to keep a steady head and reap the ultimate benefits of flying together

Flapping flight is the most energetically demanding form of sustained
forwards locomotion that vertebrates perform. Flock dynamics therefore
have significant implications for energy expenditure. Despite this, no
studies have quantified the biomechanical consequences of flying in a
cluster flock or pair relative to flying solo. Here, we compared the
flight characteristics of homing pigeons (Columba livia) flying solo and
in pairs released from a site 7 km from home, using high-precision 5 Hz
GPS and 200 Hz tri-axial accelerometer bio-loggers. As expected, paired
individuals benefitted from improved homing route accuracy, which reduced
flight distance by ~7% and time by ~9%. However, realising these
navigational gains involved substantial changes in flight kinematics and
energetics. Both individuals in a pair increased their wingbeat frequency
by ~18%, by decreasing the duration of their upstroke. This sharp increase
in wingbeat frequency caused just a 3% increase in airspeed, but reduced
the oscillatory displacement of the body by ~22%, which we hypothesise
relates to an increased requirement for visual stability and
manoeuvrability when flying in a flock or pair. The combination of the
increase in airspeed and a higher wingbeat frequency would result in a
minimum 2.2% increase in the total aerodynamic power requirements if the
wingbeats were fully optimised. Overall, the enhanced navigational
performance will offset any additional energetic costs as long as the
metabolic power requirements are not increased above 9%. Our results
demonstrate that the increases in wingbeat frequency when flying together
have previously been underestimated by an order of magnitude and force
reinterpretation of their mechanistic origin. We show that, for pigeons
flying in pairs, two heads are better than one, but keeping a steady head
necessitates energetically costly kinematics.