Onychonycteris finneyi had low aerodynamic efficiency but could flutter.
Tanzanycteris mannardi had derived echolocation.
Several hypotheses exist:
Echolocation first: Primitive echolocation used for prey detection evolved before powered flight, then lost in Pteropodidae, with convergent evolution in Rhinolophoidea and Vespertilioniformes.
Powered flight first: Echolocation linked to flight.
Gliding model: Supported by limb structure and fossils.
Convergent Evolution
Convergent evolution in laryngeal echolocation.
Mormoopidae also use CF echolocation, but produce it differently.
Pteropodidae likely lost laryngeal echolocation.
Cryptic Speciation
Tight link between echolocation, morphology, and lifestyle leads to large cryptic variation.
Over 1430 known species, but more are possible.
Diversity reflects variations in diet, roosting, and social behavior.
Echolocation
Allows bats to "see" using sound.
Three main forms:
Tongue click / wing click.
Orally emitted.
Nasally emitted.
Not all bats echolocate; some fruit bats use vision or olfaction.
Key Features of Echolocation Calls
Frequency: Low travels further but gives coarse spatial information; high attenuates quicker but reflects from small objects.
Band width.
Duration: Longer call travels further with less detail; shorter calls used in cluttered environments.
Amplitude: Louder call travels further.
Echolocation and Body Size
Increase in frequency = decrease in wavelength.
Small bat = small emitter (mouth) = broader beam.
Phases of a Call
Search phase: Widely spaced calls to detect distant objects.
Approach phase: Shorter and faster calls.
Terminal buzz phase: Just before capture.
Echolocation Modes
Oral: Frequency modulated calls with broadband sweep; self-deafening; short duration; detect fine details.
Nasal: Predominantly constant frequency calls with highly evolved cochleae; long duration calls; adjust frequency for Doppler shift; nose leaf structure creates a stable narrowband beam.
Mixing Oral and Nasal: Mouth and nasal emitting can occur simultaneously to improve accuracy and reduce energetic costs.
Evolutionary Arms Races
Bats evolve echolocation to hunt moths.
Moths evolve "ears" (tympanal organs) and escape behaviors.
Bats evolve "whispering strategy."
Butterflies move into daylight.
Flight Overview
Bat wing morphology and echolocation are tightly linked.
Aspect ratio and wing loading are important.
Bat flight is more precise than birds due to wing morphology.
Bat Wings
Convex curve of wing = air moves faster over rather than under wing = lift.
Angle of attack (AoA): Bats finely adjust AoA by changing wing shape, allowing for precise lift production and control.
Flexible wings allow AoA adjustments across different parts of the wings.
Digits reduce turbulence.
Can create thrust on both downstroke and upstroke.
Wing Shape and Flying Mode
Wide, short wings with rounded tips = manoeuvrable, slow flying.
Long, thin wings with pointed tips = fast, less agile flying.
Terrestrial Movement
Some bats, like Mystacina tuberculata, spend most of their time on the ground.
Vampire bats (Desmodus rotundus) can walk, run, and jump.
Physiological Impacts of Flight
Beat wings 10 times per second.
Take a breath on each wing beat.
Exhale late in upstroke, echolocate coinciding with wingbeat.
Heart rate increases 2-6x resting rate.
Metabolic rate during flight increases 14x rest.
Increase in body temperature.
Bat Distribution
Found on every continent except Antarctica.
Sociality in Bats
Exhibit huge diversity of social systems linked to roosting and reproductive ecology.
Use specific social calls for aggression, distress, mother-offspring communication, and courtship.
Some species recognize individuals through calls and have "friends."
Mating Strategies
Promiscuity: Swarming at mines/caves with multiple copulations and no mate guarding; common in large, dispersed populations.
Polygyny: Males select a mating roost and sing to attract a harem of females.
Lekking: Males come to singing sites to attract females; rare in mammals but used by several bat species.
Monogamy: Roost and forage together, highly territorial.
Mating disruption: Males guard females by following and being aggressive towards other males.
Roosting Strategies
Plants: Exposed roosts, tree cavities, inside carnivorous pitcher plants, large roosts in trees, inside rolled leaves.
Caves: Clumped or separate, often in crevices with important microclimatic conditions.
Hibernation: Reduce metabolic rate, decrease body temperature, reduce heart rate and respiration; involves torpor (short-term hibernation), fat stores, and periodic rousing.
Hibernation locations differ by exposure, bat condition, temporal variability, and species-specific variability.
Migration
Common strategy for accessing different food sources (tropical bats) or food/hibernation (temperate bats).
Tends to be intracontinental movements.
Partial migration is common.
Eidolon helvum: Longest migration of any African land mammal (~2500 km) with ~8 million individuals.
Tadarida brasiliensis: Largest bat colony in the world (15 million bats); climate change is causing earlier migrations.
Feeding Strategies
Carnivorous bats: Adaptations for consuming vertebrates include dome-shaped cranium, larger sagittal crest, elongated rostrum, and large bite force.
Insectivorous bats: Basal state with echolocation calls, sharp pointed teeth, large ears, and strong jaw musculature.
Nectivorous bats: Adaptations include hovering ability, elongated extensile tongues, grooves and brushlike papillae, and fast metabolism.
Sanguineous bats: Blood-feeding adaptations include specific gene loss, heat sensors in face, anticoagulants in saliva, and unusually large stretchy stomach.