Animal Behaviour: Communication 2 - Effects of Ecology and Evolution

7 Components: Sender (actor - initiates the signal), Receiver (reactor - detects and responds to the signal), Channel (medium through which signal travels), Signal (the message itself), Context (environmental and social factors influencing communication), Noise (interference), Code (rules governing signal structure and meaning).
Discrete vs. Graded Signals:
- Discrete: Single, simple message (e.g., alarm call indicating immediate danger). Often binary.
- Graded: Signals with varying intensity and complexity that communicate more nuanced information (e.g., varying levels of aggression).

4 Main Channels: Chemical (pheromones, odors), Audio (vocalizations, sounds), Visual (displays, coloration), Tactile (touch, vibrations)

Ecological Constraints: Sensory channel use varies based on ecological costs and benefits. Visual signals favored in open habitats (clear visibility); acoustic signals in dense forests (sound travels well despite obstructions). Example: Bird songs adapted to forest environments have specific frequencies to avoid sound degradation.
Responses of Reactors: Signals must effectively target the intended audience to elicit a response. The receiver's sensory capabilities and behavioral tendencies shape the evolution of signals. Signals that don't elicit the desired response are unlikely to persist.

Bert Holldöbler’s (1977) study:
- Tactile signal: recruits a single ant to stationary food (e.g., harvester ants, Leptothorax spp.) - 'tandem-running'. Used when precision is needed, and food source is reliable.
- Chemical (odor): recruits many ants to a large mobile food (e.g., fire ants Solenopsis spp.). Effective for quickly exploiting ephemeral food sources.
- Visual cues or odors: for renewable patches (e.g., Atta spp., leaf cutter ants and Pogonomyrmex). Allows for long-term exploitation of resources.

Kaspari et al. (2010): Sodium limitation affects ant feeding behavior; modified behavior and diet to increase sodium ingestion in sodium-limited areas. Demonstrates how environmental factors can influence communication strategies.

Affected by habitat structure and meteorological conditions. Signal propagation is influenced by environmental factors.
- Rufous-collared sparrow: slower trills in forests than in open country. Avoids signal degradation due to reverberation.
- Great tits: narrower frequency range, lower max frequency, and fewer notes in dense forests compared to open country. Optimizes signal clarity in complex environments.

Signals evolve to increase effectiveness in altering reactor behavior. Natural selection favors signals that are easily detected and interpreted.
Reactors play a key role in signal origin and subsequent evolution toward increased effectiveness. The receiver's response shapes the evolution of the signal.
Lorenz and Tinbergen: Many signals evolved from incidental movements or responses of actors that happened to be informative to reactors; also evolved from intention movements. This highlights the opportunistic nature of signal evolution.

Functional movements that evolve into signals. Provide insight into an animal's readiness to perform an action.
- Characteristics: Often exaggerated for visibility or interpretation; retain some association with their original function. Exaggeration enhances clarity; retention provides context.

Pelicans and Gannets: Pre-takeoff movements, where crouching postures signal readiness to fly. These movements communicate imminent departure.
Cormorants (Phalacrocorax): Wing-waving behaviors, including slow and alternate wing movements. These display social signals.
Pelagic Shag (Phalacrocorax pelagicus): Rapid-flutter wing-waving, a ritualized display for courtship or territorial signaling; evolution of functional movements into ritualized signals. Demonstrates how behaviors can be co-opted for communication.

Original Function: Defensive or fearful reaction. Initially a response to threat.
Communication Function: Submissive signal to prevent aggression or appease a dominant individual. Reduces the likelihood of conflict.

Behaviors irrelevant to the current context, occurring in stress or during conflicting motivations. These activities seem out of place.
- Mechanisms: Result from conflicting motivations; may reduce tension or redirect focus. Provide an outlet for pent-up energy.

Stress or Conflict Origin: Arise in motivational conflict (e.g., fight or flight, courtship vs. fear). Situations where an animal experiences competing drives.
Evolution into Signals: Precursors to ritualized signals.
- Examples: (1) Preening evolved into courtship signals in ducks; (2) Grass-pulling became a ritualized display in herring gulls. These behaviors have been co-opted for communication.
Relief of Stress: Behaviors might help reduce tension or avoid escalation of aggressive interactions. Act as a safety valve in tense situations.

Ritualisation: Displacement activities become exaggerated and stereotyped, evolving into communicative signals (