Comparative Behavior Lecture 8

What is neuroethology?

Neuroethology is the study of how the nervous system (especially sensory and central nervous systems) controls natural behavior, combining both proximate (neuroscience) and ultimate (evolutionary) perspectives.

What does neuroethology investigate?

It explores how sensory stimuli are translated into behavior, how behaviors are controlled by neural mechanisms, and how natural selection shapes those mechanisms.

How do neurons transmit signals?

Through all-or-nothing action potentials; behavior intensity is modulated by the frequency of firing and the number of neurons firing.

What are neural circuits?

Groups of interconnected neurons that carry out specific functions and regulate themselves via feedback loops in response to stimuli.

What is brain plasticity?

The brain's ability to change neural connections due to experience, including learning, stress, hormones, aging, and environment.

What was Tinbergen’s contribution to neuroethology?

He studied fixed action patterns, such as chick begging behavior triggered by a red dot on a gull's bill, and discovered the idea of sign stimuli and innate releasing mechanisms.

What is a fixed action pattern (FAP)?

A sequence of innate behaviors that proceeds to completion once triggered by a specific stimulus.

What is a sign stimulus or releaser?

A simple, specific external stimulus that triggers a fixed action pattern (e.g., red dot on a gull’s beak).

What is a supernormal stimulus?

An exaggerated version of a natural stimulus that elicits a stronger-than-normal behavioral response (e.g., an artificial bill with a large red

How does egg rolling in geese illustrate a fixed action pattern?

When an egg rolls out, the goose rolls it back even if the egg is removed midway — showing the behavior continues after stimulus is gone.

What role do mouth markings play in finches?

They act as species-specific releaser stimuli for parental feeding behavior, likely evolved due to brood parasitism.

How did brood parasites evolve in this context?

Brood parasitic chicks evolved to mimic host species' mouth markings, triggering feeding behavior — an evolutionary arms race.

What is feature detection?

The nervous system’s ability to filter and recognize important stimuli (e.g., prey, mates) from background noise.

What was Jörg-Peter Ewert’s discovery about toad vision?

Toads snap at horizontal moving bars but not vertical ones, revealing specific neurons (prey detectors) in the optic tectum that process prey-relevant stimuli.

What happens when specific brain regions in toads are stimulated?

Stimulating the thalamic area causes escape behavior, while stimulating the prey detector region triggers snapping — supporting that behavior is tied to specific neural circuits.

What behavior does stimulating prey-selective neurons in frogs induce?

It induces the snapping behavior, suggesting these neurons regulate the frog’s response to prey stimuli.

What is a well-studied example of vocal communication in fish?

The plainfin midshipman fish, which has two types of males exhibiting different vocal and reproductive behaviors.

What are the characteristics of type I male midshipman fish?

They are large, build nests, defend them, court females, and produce vocalizations like grunts and hums.

How do type II male midshipman fish differ from type I males?

They are smaller, nonvocal, do not build nests, and use a sneaker strategy to fertilize eggs by sneaking into nests and releasing sperm.

Why are type II and type I male midshipman fish considered a polyphenism?

Because they are two distinct forms within a species, resulting from different developmental pathways and both being adaptive strategies.

What neural and anatomical differences are found between type I and type II males?

Type I males have larger sonic muscles, faster pacemaker neuron firing rates, larger motor neurons, and larger VMN brain nuclei; type II males have larger gonads and reach sexual maturity faster.

Why are both male types considered alternative reproductive tactics?

Each strategy has trade-offs and benefits, and both can be adaptive depending on the population's social environment.

What problem did researchers in the 1950s investigate about bats?

How bats, which are nocturnal, can catch flying insects in the dark.

What did Don Griffin discover about bat behavior?

That bats use echolocation, emitting high-frequency sounds and listening to the returning echoes to navigate and locate prey.

What changes occur in bat calls as they close in on prey?

The calls become more rapid, culminating in a fast “buzz” just before capturing prey.

How did experiments demonstrate that hearing, not vision, is critical for bats in navigation?

When bats’ ears were covered, they ran into wires more often, but covering the eyes did not affect navigation performance significantly.

What is spherical spreading loss?

It refers to the reduction in sound intensity as it spreads out from the source; high-frequency sounds lose intensity over shorter distances.

Why is spherical spreading loss important in the context of bat echolocation?

Because bats use high-frequency calls that attenuate quickly, requiring them to have very sensitive hearing at those frequencies.

What is an audiogram and what does it measure?

An audiogram shows an animal’s hearing threshold across different frequencies—how loud a sound must be at each frequency to be heard.

Why do human audiograms show best sensitivity between 2–4 kHz?

Because this is the frequency range of human speech, which is most relevant to us.

How do audiograms differ between species like elephants and mice?

Elephants hear best at low frequencies matching their vocalizations, while mice hear best at higher frequencies relevant to their communication.

What does the audiogram of the Greater Horseshoe Bat reveal?

It has three peaks of best hearing sensitivity that correspond to different types of calls: social calls, modified social

What is notable about the audiogram of the mustached bat?

Although it produces calls with peak energy at 61 kHz, its best neural hearing is at 62 kHz, indicating a fine-tuned auditory system for detecting echoes.

Why is there a mismatch between the frequency of the bat’s calls and the frequency of its best hearing sensitivity?

The mismatch is explained by the Doppler effect, which causes the bat to perceive echoes at a slightly higher frequency than the calls it produces because it is flying relative to the object it is echolocating.

What is the Doppler effect?

The Doppler effect is the change in the perceived frequency (pitch) of a sound wave when the listener is moving relative to the sound source. For example, a car horn sounds higher pitched as it approaches and lower pitched as it moves away.

How does the Doppler effect relate to bats echolocating while flying?

As bats fly towards objects, the echoes they hear are shifted to a higher frequency than their calls due to the Doppler effect. This explains why their best hearing sensitivity is tuned to a frequency slightly higher than the call they produce.

How do some bats compensate for the Doppler effect?

Some bats behaviorally compensate by adjusting the frequency of their calls downward as they fly toward objects, keeping the perceived echoes at a stable frequency range for echolocation.

What did researchers Pain and Drury discover about barn owls in the 1950s?

They demonstrated that barn owls can locate mice acoustically in complete darkness, pouncing on sounds made by a paper ball dragged behind the mouse rather than the mouse itself, showing owls rely on purely acoustic cues to catch prey.

What physical adaptations help owls localize sound?

Owls have facial symmetry shaped like a parabola to focus sound, ear flaps positioned asymmetrically (right ear lower and pointing upward, left ear higher and pointing downward), and special facial feathers—all enhancing their ability to detect subtle differences in sound arrival time and loudness between ears.

What is the significance of interaural time differences for owls?

Interaural time differences occur because a sound arrives at one ear slightly before the other, helping the owl determine the direction of the sound source, an important cue for localizing prey.

How do owls’ ear movements aid in sound localization?

Like dogs and cats, owls can adjust their ears independently to emphasize interaural time and loudness differences, improving their ability to locate sounds.

What did neuroethologists Marconishi and Nidsen discover about the barn owl's brain?

They identified two parallel neural pathways processing interaural time and loudness differences, and found a spatial auditory map in the owl’s midbrain (inferior colliculus) with space-specific neurons tuned to sounds from particular directions.

What are space-specific neurons in the barn owl’s brain?

These neurons respond selectively to auditory signals coming from specific directions, helping the owl map sounds in space for precise localization.

How do the physical and neurological adaptations of barn owls work together?

The physical features focus and collect sound, while the brain's parallel processing pathways and space-specific neurons decode directional information, giving owls exceptional ability to use sound to locate prey.

What will the next lecture in this neuroethology series discuss?

It will cover bats versus prey adaptations in response to biological sonar and introduce the concept of categorical perception, a brain phenomenon that filters important biological stimuli from sensory noise.