Field Flight Dynamics of Hummingbirds during Territory Encroachment and Defense

Abstract

Hummingbirds are known to defend food resources such as nectar sources from encroachment by competitors (including conspecifics). These competitive intraspecific interactions provide an opportunity to quantify the biomechanics of hummingbird flight performance during ecologically relevant natural behavior. We recorded the three-dimensional flight trajectories of Ruby-throated Hummingbirds defending, being chased from and freely departing from a feeder. These trajectories allowed us to compare natural flight performance to earlier laboratory measurements of maximum flight speed, aerodynamic force generation and power estimates. During field observation, hummingbirds rarely approached the maximal flight speeds previously reported from wind tunnel tests and never did so during level flight. However, the accelerations and rates of change in kinetic and potential energy we recorded indicate that these hummingbirds likely operated near the maximum of their flight force and metabolic power capabilities during these competitive interactions. Furthermore, although birds departing from the feeder while chased did so faster than freely-departing birds, these speed gains were accomplished by modulating kinetic and potential energy gains (or losses) rather than increasing overall power output, essentially trading altitude for speed during their evasive maneuver. Finally, the trajectories of defending birds were directed toward the position of the encroaching bird rather than the feeder.

Hummingbirds control turning velocity using body orientation and turning radius using asymmetrical wingbeat kinematics

“…Taken together, these studies illustrate how body-dependent and -independent kinematic mechanisms are employed along a continuum of turning manoeuvres. Feeder tracking studies provide an experimental approach for manipulating manoeuvring performance in hummingbirds but the range of movements is necessarily limited relative to the diversity of flight trajectories observed in natural conditions [38,39]. The radii used in the current study (0.23 and 0.33 m) are similar to those used by free-flying hummingbirds performing arcing turns in a large laboratory cage (mean ¼ 0.48 m) [40].…”

Flight mechanics and control of escape manoeuvres in hummingbirds II. Aerodynamic force production, flight control and performance limitations

“…For these miniature vertebrate fliers, mastering a repertoire of controlled aerobatic manoeuvres is essential for their aerial survival (Altshuler, 2006;Clark, 2011;Sholtis et al, 2015) and sexual selection (Clark, 2009;Clark et al, 2011;Stiles, 1982). In a companion paper (Cheng et al, 2016), we studied the kinematic patterns of one such manoeuvre, an escape response consisting of drastic body pitch and roll rotations combined with large unidirectional linear acceleration.…”

Into rude air: hummingbird flight performance in variable aerial environments

“…In the spatial domain, sharp gradients in airflow can also present distinct challenges to flight control. For example, hawkmoths hover-feeding within tornado-like vortices (with transverse speeds up to 1.2 m s 21 and a swirl ratio of 0.11) asymmetrically alter their stroke plane angles and wing angles of attack to sustain continuous turns in yaw [34]. Nectar-feeders more generally must maintain position while hovering at flowers, and a broad spectrum of aerial disturbances (imposed either symmetrically or asymmetrically) must characterize their natural flight.…”

“…The relatively small body sizes of hummingbirds have, to date, precluded attachment of accelerometers and data loggers, and patterns of movement ecology and associated costs remain obscure. Recent work on intraspecific aerial interactions, however, documents intense and energetically demanding manoeuvres [18,21]. Manoeuvring to capture small insect prey in mid-air is also an obligate feature of hummingbird biology, but neither this nor many other interesting flight behaviours (e.g.…”