Volume 26, Issue 24, Pages 3368-3374 (December 2016) Mechanical Constraints on Flight at High Elevation Decrease Maneuvering Performance of Hummingbirds  Paolo S. Segre, Roslyn Dakin, Tyson J.G. Read, Andrew D. Straw, Douglas L. Altshuler  Current Biology  Volume 26, Issue 24, Pages 3368-3374 (December 2016) DOI: 10.1016/j.cub.2016.10.028 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 We Tested Maneuvering Performance across Elevations and in Physically Variable Gas Mixtures (A) Both air density and oxygen availability decrease at higher elevations. We tested how these two physiological challenges influence maneuverability by performing a translocation experiment to test the difference between high- and low-altitude habitats (H1) and a gas substitution experiment to test the independent effects of air density (H2) and oxygen availability (H3). (B) All experiments were conducted with male Anna’s hummingbirds (Calypte anna). (C) The free flight maneuvers of single and paired hummingbirds were recorded using synchronized cameras mounted above a 3 m × 1.5 m × 1.5 m chamber. The chamber included a single feeder and several perches. Local computers performed 2D tracking in each camera view, and the output was streamed to a central computer for 3D tracking. The trace in (C) shows the body position (blue circle) and orientation (red line) for one bird chasing a competitor. See Movie S1 for a video of this sequence. Photo by Benjamin Goller. See also Movie S2 and Figures S3 and S4. Current Biology 2016 26, 3368-3374DOI: (10.1016/j.cub.2016.10.028) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 2 Maneuvering Performance Decreases at High Elevation (A–F) Profiles are shown for eight stereotyped maneuvers described in the text, including six translational and rotational maneuvers (A–C) and two types of complex turns (D–F). The lines in (A) and (D) show the pooled population averages, with shaded 25th and 75th percentiles, for all but the arcing turns. To illustrate the variation in arcing turn radius, all of the recorded arcing turn sequences are represented in (D) using semi-transparent colored lines. See Figure S1 for examples of single maneuvers. Average profiles for individual birds are shown in (B) and (E). Green shading in (B) and (E) is used to indicate the times when a bird’s performance at low elevation exceeded its performance at high elevation; purple shading indicates the reverse (i.e., performance at high elevation exceeded performance at low elevation). Note that for decelerations, pitch-down velocities, and yaw velocities, we took the absolute values so that larger values indicate more rapid decelerations or rotations. (C and F) At high elevation (3,800 m), the birds’ speeds, accelerations, and rotational velocities were significantly reduced (C). Performance of arcing turns was also poorer at high elevation, and yet the birds used proportionately more arcing turns and fewer pitch-roll turn maneuvers (i.e., they turned on a dime less often) (F). All values in (C) and (F) are expressed relative to the population grand mean for the low-elevation site, with points representing the means for individual birds and thick black lines indicating the grand means in each treatment. An asterisk denotes a statistically significant effect of elevation. See also Tables S1 and S2. Current Biology 2016 26, 3368-3374DOI: (10.1016/j.cub.2016.10.028) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 3 Flight Maneuvers in Variable Gas Mixtures (A–D) Profiles are shown for eight stereotyped maneuvers in the gas substitution experiment, comparing flight in hypodense conditions (A and B) and hypoxic conditions (C and D) to sea-level air. Note that the control dataset (“air”) is the same in each case. Plots in (A) and (C) show the pooled population averages and 25th and 75th percentiles (with the exception of arcing turns, where all of the maneuvers are shown to illustrate the variation in turn radius, as in Figure 2). Average profiles for individual birds are shown in (B) and (D), with colored shading to indicate the within-individual effects of the gas treatments. In (B), green shading indicates times when a bird’s performance in sea-level air exceeded its performance in hypodense gas (and pink indicates the reverse). In (D), green shading indicates times when a bird’s performance in sea-level air exceeded its performance in hypoxic gas (and blue shading indicates the reverse). Current Biology 2016 26, 3368-3374DOI: (10.1016/j.cub.2016.10.028) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 4 Maneuvering Performance Decreases as a Result of Air Density, Not Oxygen Availability (A) When challenged to fly in hypodense normoxic gas (air density equivalent: 3,800 m), the birds exhibited decreases in their accelerations, decelerations, and rotational velocities. They also took more time to complete pitch-roll turns. (B) When challenged to fly in normodense hypoxic gas (oxygen equivalent: 3,925 m), there was no significant change in maneuvering performance as compared to flying in sea-level air. All values are expressed relative to the population grand mean for the control group (sea-level air). Points show the means for individual birds, and thick black lines show the grand means in each treatment. An asterisk denotes a statistically significant effect. See Figure S2 for performance metrics that were not significantly influenced by the gas substitution treatments, as well as metrics that were associated with time in captivity. See also Tables S1 and S2. Current Biology 2016 26, 3368-3374DOI: (10.1016/j.cub.2016.10.028) Copyright © 2016 Elsevier Ltd Terms and Conditions