Comparing Aerodynamic Efficiency in Birds and Bats Suggests Better Flight Performance in Birds

Flight is one of the energetically most costly activities in the animal kingdom, suggesting that natural selection should work to optimize flight performance. The similar size and flight speed of birds and bats may therefore suggest convergent aerodynamic performance; alternatively, flight performance could be restricted by phylogenetic constraints. We test which of these scenarios fit to two measures of aerodynamic flight efficiency in two passerine bird species and two New World leaf-nosed bat species. Using time-resolved particle image velocimetry measurements of the wake of the animals flying in a wind tunnel, we derived the span efficiency, a metric for the efficiency of generating lift, and the lift-to-drag ratio, a metric for mechanical energetic flight efficiency. We show that the birds significantly outperform the bats in both metrics, which we ascribe to variation in aerodynamic function of body and wing upstroke: Bird bodies generated relatively more lift than bat bodies, resulting in a more uniform spanwise lift distribution and higher span efficiency. A likely explanation would be that the bat ears and nose leaf, associated with echolocation, disturb the flow over the body. During the upstroke, the birds retract their wings to make them aerodynamically inactive, while the membranous bat wings generate thrust and negative lift. Despite the differences in performance, the wake morphology of both birds and bats resemble the optimal wake for their respective lift-to-drag ratio regimes. This suggests that evolution has optimized performance relative to the respective conditions of birds and bats, but that maximum performance is possibly limited by phylogenetic constraints. Although ecological differences between birds and bats are subjected to many conspiring variables, the different aerodynamic flight efficiency for the bird and bat species studied here may help explain why birds typically fly faster, migrate more frequently and migrate longer distances than bats

The SPIRITS Sample of Luminous Infrared Transients: Uncovering Hidden Supernovae and Dusty Stellar Outbursts in Nearby Galaxies

We present a systematic study of the most luminous (M IR [Vega magnitudes] brighter than −14) infrared (IR) transients discovered by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) between 2014 and 2018 in nearby galaxies (D 12) show multiple, luminous IR outbursts over several years and have directly detected, massive progenitors in archival imaging. With analyses of extensive, multiwavelength follow-up, we suggest the following possible classifications: five obscured core-collapse supernovae (CCSNe), two erupting massive stars, one luminous red nova, and one intermediate-luminosity red transient. We define a control sample of all optically discovered transients recovered in SPIRITS galaxies and satisfying the same selection criteria. The control sample consists of eight CCSNe and one Type Iax SN. We find that 7 of the 13 CCSNe in the SPIRITS sample have lower bounds on their extinction of 2 < A V < 8. We estimate a nominal fraction of CCSNe in nearby galaxies that are missed by optical surveys as high as ${38.5}_{-21.9}^{+26.0} \%$ (90% confidence). This study suggests that a significant fraction of CCSNe may be heavily obscured by dust and therefore undercounted in the census of nearby CCSNe from optical searches

El deterioro de la política educativa, científica y tecnológica destinada al ámbito rural

Como parte de la crisis capitalista que vive México, el abandono al sector educativo, científico y tecológico relacionado con el medio rural es alarmante. Más aún si se le compara con la participación de la educación en las actividades agropecuarias durante la década de los treinta y principios de los cuarenta en el siglo XX. Sin embargo, el sistema nacional de educación agrícola superior, surgió sin planeación y criterios definidos que integren la educación destinada al sector agropecuario con los intereses campesinos jornaleros, ejidatarios y comuneros del país

The physics of animal locomotion

In this chapter the physics behind animal movement, the adaptations found in locomotion to generate forces, and the mechanisms reducing the cost of transport are discussed. The ability to minimize costs and maximize movement speed is part of the biomechanical physics of animal locomotion. For any type of active movement (e.g. walking, running, swimming, or flying), the animal is required to produce forces to overcome resistance and in many cases also gravity. For terrestrial locomotion, this is achieved by generating ground reaction forces, while in air and water by generating fluid dynamic forces. Due to scaling laws in physics, the speed that can be achieved and the cost of transport are correlated with the size of the animal. Moving across scales thus has consequences for our expectations regarding animal movement, including the occurrence of seasonal migrations, which may be limited by the speed and cost of locomotion

Tomo processed 5 ms-1

Vector fields of the wake of pied flycatchers flying in a wind tunnel. Dat files containing columns of x, y, z coordinates in mm and the corresponding velocity components (Vx, Vy, Vz in ms-1). The coordinate system is right handed with x is horizontally to the right, y is vertically upwards and z is out of the xy-plane

Body lift, drag and power are relatively higher in large-eared than in small-eared bat species

Bats navigate the dark using echolocation. Echolocation is enhanced by external ears, but external ears increase the projected frontal area and reduce the streamlining of the animal. External ears are thus expected to compromise flight efficiency, but research suggests that very large ears may mitigate the cost by producing aerodynamic lift. Here we compare quantitative aerodynamic measures of flight efficiency of two bat species, one large-eared (Plecotus auritus) and one small-eared (Glossophaga soricina), flying freely in a wind tunnel. We find that the body drag of both species is higher than previously assumed and that the large-eared species has a higher body drag coefficient, but also produces relatively more ear/body lift than the small-eared species, in line with prior studies on model bats. The measured aerodynamic power of P. auritus was higher than predicted from the aerodynamic model, while the small-eared species aligned with predictions. The relatively higher power of the large-eared species results in lower optimal flight speeds and our findings support the notion of a trade-off between the acoustic benefits of large external ears and aerodynamic performance. The result of this trade-off would be the ecomorphological correlation in bat flight, with large-eared bats generally adopting slow-flight feeding strategies