Biology subjects

Garde, B.

Publications and source records attributed to Garde, B..

4 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↗

bioRxiv2021

Ecological inference using data from accelerometers needs careful protocols

O_LIAccelerometers in animal-attached tags have proven to be powerful tools in behavioural ecology, being used to determine behaviour and provide proxies for movement-based energy expenditure. Researchers are collecting and archiving data across systems, seasons and device types. However, in order to use data repositories to draw ecological inference, we need to establish the error introduced according to sensor type and position on the study animal and establish protocols for error assessment and minimization. C_LIO_LIUsing laboratory trials, we examine the absolute accuracy of tri-axial accelerometers and determine how inaccuracies impact measurements of dynamic body acceleration (DBA), as the main acceleration-based proxy for energy expenditure. We then examine how tag type and placement affect the acceleration signal in birds using (i) pigeons Columba livia flying in a wind tunnel, with tags mounted simultaneously in two positions, (ii) back- and tail-mounted tags deployed on wild kittiwakes Rissa tridactyla. Finally, we (iii) present a case study where two generations of tag were deployed using different attachment procedures on red-tailed tropicbirds Phaethon rubricauda foraging in different seasons. C_LIO_LIBench tests showed that individual acceleration axes required a two-level correction (representing up to 4.3% of the total value) to eliminate measurement error. This resulted in DBA differences of up to 5% between calibrated and uncalibrated tags for humans walking at different speeds. Device position was associated with greater variation in DBA, with upper- and lower back-mounted tags in pigeons varying by 9%, and tail- and back-mounted tags varying by 13% in kittiwakes. Finally, DBA varied by 25% in tropicbirds between seasons, which may be attributable to tag attachment procedures. C_LIO_LIAccelerometer accuracy, tag placement, and attachment details critically affect the signal amplitude and thereby the ability of the system to detect biologically meaningful phenomena. We propose a simple method to calibrate accelerometers that should be used prior to deployments and archived with resulting data, suggest a way that researchers can assess accuracy in previously collected data, and caution that variable tag placement and attachment can increase sensor noise and even generate trends that have no biological meaning. C_LI

animal behavior and cognition↗

bioRxiv2021

Fine-scale changes in speed and altitude suggest protean movements in homing pigeon flights

The flight speeds that animals should adopt to minimise energy expenditure in different scenarios can be predicted by the curve of power against speed. However, relatively few studies have examined how animals respond to the landscape below them, which could affect speed through modifications in climb rate and perceived predation risk. We equipped homing pigeons (Columba livia) with high frequency loggers to examine how flight speed varies in relation to topography and land cover, predicting that these parameters may have a substantial impact on flight speed and hence cost. Pigeons showed mixed evidence for an energy saving strategy, as they minimised climb rates by starting their ascent ahead of hills, but selected rapid speeds in their ascents. Birds did not modify their speed substantially in relation to land cover, but higher speeds were observed during descending flight, highlighting the importance to consider the rate of change in altitude before estimating power use from speed. Finally, we document an unexpected variability in speed and altitude over fine scales; a source of substantial inefficiency. We suggest this may a form of protean behaviour adopted to reduce predation risk when flocking is not an option, and that such a strategy could be widespread.

animal behavior and cognition↗