Acoustic Communication #7

What are the five main sensory modalities used in animal communication?

- Hearing (acoustic signals)

- Vision (visual signals)

- Touch (tactile signals)

- Smell/taste (chemical signals)

- Electroreception (electrical signals)

What are the main disadvantages of acoustic signals in animal communication?

- Energetically inefficient (typically < 5%)

- Interferes with other activities (breathing, feeding)

- Low persistence – need to keep making the call

- Difficult to directionalize

- Subject to eavesdropping (competitors, predators)

What are compound signals?

- Communication signals with more than one intended receiver or purpose

- Example: Fish and bird songs used to:

  - Advertise to potential mates

  - Establish territorial boundaries

What are multimodal signals and give an example?

- Communication signals composed of multiple signal modalities used in combination

- Example: Combined acoustic and visual displays

- Used in fish and bird mate attraction displays

- Individual parts do not work on their own

What is the persistence issue with acoustic signals?

- Acoustic signals have low persistence

- Animals need to keep making the call repeatedly

- Signals don't last in the environment after being produced

What are the two ways communication systems can be transmitted?

1. Vertical transmission (genetically inherited) - Example: courtship calls in fish and amphibians are instinctive

2. Lateral transmission (learned from others) - Example: vocal learning in birds, cetaceans, elephants, and some primates

What is vocal learning?

The modification of vocal signals based on the vocal signals that conspecifics are making. It is relatively rare and found in birds, cetaceans, elephants, and some primates.

What is an Evolutionarily Stable Strategy (ESS)?

A strategy (behavior) that is stable in a population and is resistant to replacement by alternate strategies.

What must be true for a communication system to be an ESS?

- Must be subject to natural selection

- Net benefit of communication must be positive

- Benefits must outweigh costs

What is Fisherian selection (runaway sexual selection)?

A process where:

- Females prefer more elaborate songs (increased song complexity indicates increased male fitness)

- Over time, males develop more and more elaborate calls

- Females prefer more and more elaborate calls

- This creates a self-reinforcing cycle across generations

What is the key question about maintaining honest signals?

What stops males from simply exaggerating their songs to gain access to more females?

What are three hypotheses that explain how communication signals remain honest?

1. Zahavi's handicap principle

2. Indices

3. Common interest

What is Zahavi's handicap principle?

A theory explaining how elaborate advertisement signals (like long bird songs or peacock tails) remain honest. Reliable signals must be costly to the sender, creating a trade-off between sexual selection and natural selection.

Why is there motivation to deceive in sexual display signals?

There is great motivation to exaggerate sexual display signals for increased mating success. However, Zahavi's principle explains why this doesn't lead to dishonest signaling.

What is the trade-off in Zahavi's handicap principle?

A trade-off between:

- Sexual selection (attracting mates)

- Natural selection (survival)

Elaborate signals help with mating but reduce survival ability.

Why can't less fit individuals "bluff" their signals?

Less fit individuals cannot afford to make the signal, therefore they cannot afford to "bluff" the signal. Only truly fit individuals can bear the cost.

What is notable about skylark songs?

- Have elaborate songs and often sing in flight

- Some individuals continue singing even while being pursued by avian predators

What are two types of constraints that lead to honest signals?

1. Handicap Principle: Costly signals that only high-quality individuals can afford

2. Indices: Signals physically limited by the feature being advertised (cannot be bluffed)

why are pair-bonding signals honest in birds?

- Found in various birds

- Chick survival increases if pair bonding is stronger

- Mutual benefits to keep signals honest

- Both partners benefit from honest communication

What is aposematism?

- The use of conspicuous signals to advertise that you are unpalatable or dangerous

- Example: Unpalatable tiger moths make ultrasonic predator (bat) deterrent calls

What is Batesian mimicry?

- Mimicking the aposematic signals of a dangerous or unpalatable species

- Example: Palatable pyralid moths make predator deterrent calls of tiger moths to decrease risk of predation

- The mimic benefits by appearing dangerous when it's actually harmless

How do tiger moths and pyralid moths differ in their signaling?

- Tiger moths: Unpalatable, make ultrasonic bat deterrent calls (honest signal)

- Pyralid moths: Palatable, mimic tiger moth calls to avoid predation (dishonest signal/Batesian mimicry)

What feeding strategy does the fork-tailed drongo use?

 The fork-tailed drongo is partially kleptoparasitic, meaning it steals food from other animals.

- Follows groups of other animals

- Produces dishonest alarm calls (falsely announcing presence of a predator)

- Steals abandoned food when animals flee

What is the first condition for dishonest signals to be an ESS?

They must occur at a low frequency so that the signal benefits receivers most of the time. Example: Bats probably encounter pyralid moths rarely enough that their deceptive signaling strategy is an ESS.

What is the second condition for dishonest signals to be an ESS?

 The cost of ignoring an honest signal must be very high compared to the cost of paying attention to a dishonest signal. Example: Fork-tailed drongo - the cost of being eaten >> the cost of losing a meal. Drongos are still honest about half the time.

What is echolocation and how does it work?

- Pulses of sound used to detect and identify objects in front of the animal (e.g., obstructions, prey)

- Time between sound production and echo return indicates the distance to the object

- The frequency content of the echo indicates what the object is (e.g., size, composition), direction it's traveling, etc.

What are the characteristics of Frequency Modulated (FM) echolocation?

- Uses broadband "sweeps" (frequency decreases over time)

- Very precise range discrimination (can distinguish targets 0.5 mm apart)

- Good for cluttered environments (e.g., forests)

- Somewhat range limited

- Example: Common pipistrelle

What are the characteristics of Constant Frequency (CF) echolocation?

- Uses narrow band tones (frequency stays constant over time)

- Information on object position and movement determined through Doppler shifts

- Longer range than FM signals

- Good for open environments free of clutter

- Example: Greater horseshoe bat

Which echolocation type is better for forests and why?

Frequency Modulated (FM) echolocation is better for forests because it provides very precise range discrimination, allowing bats to navigate cluttered environments with many obstacles.

Which echolocation type is better for open environments and why?

Constant Frequency (CF) echolocation is better for open environments because it has longer range than FM signals and works well in areas free of clutter.