Biology subjects

Lempidakis, E.

Publications and source records attributed to Lempidakis, E..

3 recordsLinked to original sources

bioRxiv2024

Changing air density affects flight costs in low-flying birds

Regional patterns in wind underpin the low-cost migratory flyways of billions of birds and insects1-3, but how large-scale changes in temperature affect flight is unknown. Flight costs should increase with rising temperatures, because lift decreases as density decreases, whereas weight remains unchanged. The effects of air density on flight costs are well-established in the context of high-altitude movements and migration4-7. Here, we examine the impact of air density on low-flying birds, in relation to seasonal, regional and global changes in temperature. Using multi-sensor loggers, we find that air density was the most important predictor of wingbeat frequency in red-tailed tropicbirds (Phaethon rubricauda) breeding year-round in Mauritius. Lower air densities in the Austral summer were associated with a small but significant increase in mean wingbeat frequency, which translated to an estimated 1-2% increase in flight costs. The variation in flight costs increased by an order of magnitude when considered in space, rather than time, with flight costs varying by [≥] 10 % across the tropicbirds range. Changes in air density can therefore be an important determinant of flight costs even when birds are operating close to sea-level. Indeed, mapping air density at sea-level revealed that global temperature gradients cause effective altitude to vary by >2 km when considered as seasonal averages. This "invisible topography" at sea-level could have influenced the biogeography of flight morphologies and life-history traits.

zoology↗

bioRxiv2022

The role of wingbeat frequency and amplitude in flight power

Body-mounted accelerometers provide a new prospect for estimating power use in flying birds, as the signal varies with the two major kinematic determinants of aerodynamic power: wingbeat frequency and amplitude. Yet wingbeat frequency is sometimes used as a proxy for power output in isolation. There is therefore a need to understand which kinematic parameter birds vary and whether this is predicted by flight mode (e.g., accelerating, ascending/descending flight), speed or morphology. We investigate this using high-frequency acceleration data from (i) 14 species flying in the wild, (ii) two species flying in controlled conditions in a wind tunnel and (iii) a review of experimental and field studies. While wingbeat frequency and amplitude were positively correlated, R2 values were generally low, supporting the idea that parameters can vary independently. Indeed, birds were more likely to modulate wingbeat amplitude for more energy-demanding flight modes, including climbing and take-off. Nonetheless, the striking variability even within species and flight types, highlights the complexity of describing the kinematic relationships, which appear sensitive to both the biological and physical context. Notwithstanding this acceleration metrics that incorporate both kinematic parameters should be more robust proxies for power than wingbeat frequency alone.

biophysics↗

bioRxiv2022

Pelagic seabirds reduce risk by flying into the eye of the storm

Cyclones can cause mass mortality of seabirds, sometimes wrecking thousands of individuals. The few studies to track pelagic seabirds during cyclones show they tend to circumnavigate the strongest winds. We tracked adult shearwaters in the Sea of Japan over 11 years and find that the response to cyclones varied according to the wind speed and direction. In strong winds, birds that were sandwiched between the storm and mainland Japan flew away from land and towards the eye of the storm, flying within [≤] 30 km of the eye and tracking it for up to 8 hours. This exposed shearwaters to some of the highest wind speeds near the eye wall ([≤] 21 m s-1), but enabled them to avoid strong onshore winds in the storms wake. Extreme winds may therefore become a threat when an inability to compensate for drift could lead to forced landings and collisions. Birds may need to know where land is in order to avoid it. This provides additional selective pressure for a map sense and could explain why juvenile shearwaters, which lack a map sense, instead navigating using a compass heading, are susceptible to being wrecked. We suggest that the ability to respond to storms is influenced by both flight and navigational capacities. This may become increasingly pertinent due to changes in extreme weather patterns. Significance StatementCyclones can cause billions of dollars of damage and loss of human life. They can also cause mass mortality and strandings in seabirds. We used GPS tracking data from streaked shearwaters breeding in the worlds most active cyclone basin to understand how seabirds respond to these systems. Birds varied their response according to the wind speed and direction, generally flying towards the eye of the cyclone in strong winds. This surprising strategy enables dynamic soaring birds to control their exposure to risky wind vectors that could drift them onshore. Nonetheless, birds may need to know where land is in order to avoid it. Juveniles lack this "map sense", making them susceptible to wrecking in some scenarios.

ecology↗