There are (at least) two individuals involved in communication: the sender and the receiver of information. Senders and receivers can come from the same species (social communication) or from different species (ecological communication).

Remember that when studying animal behavior, including communication, we cannot consider the internal mental state of the animals. We cannot measure an animal's intentions or consciousness. Rather, we are limited to measuring behavior: What behavioral signals does a communicating animal send? What behavioral responses does a receiver make to those signals?

Communication involves the transfer of information. Information can be defined as a stimulus that influences the probability of behavior. Information is made up of various forms of energy that can be detected by an animal.

Information theory: Models the reduction in uncertainty of an occurrence (for example, behavior) as a means of measuring the flow of information.

Information is measured in bits= log base 2 (number of acts).

 u= measure of uncertainty (entropy). More information = less uncertainty.

Markov Chain: How much does knowing previous act(s) reduce our uncertainty about next act?

Semi-Markovian chain: common in animal behavior. Few stimuli produce deterministic responses- behavior is usually probabilistic.

 Imaging that behavior occurs in sequences:

Behavior 1 -- behavior 2 -- behavior 3, etc.

Signal from sender -- Response by receiver

 We can study the amount of information by plotting:

u0= log base 2 (total number acts possible). This represents the total amount of information available.

u1= correction for different rates of performance of different acts. -Sum p(x) log₂ p(x)

u2= effect of previous act on next act.

We analyze information by plotting u values on a bar chart- where do large drops in uncertainty occur? Does knowing the behavior of the sender tell us a lot about what the receiver will do? If so, then the animals are communicating. 

Definition of communication. Proposed by E.O. Wilson - Action on the part of one animal that alters the probability of behavior in another animal, such that the sender, the receiver, or both benefit (benefit in terms of RS). 

Following Wilson's definition, we can identify several categories of communication, based on the fitness effects on the sender and receiver.

Fitness effects on:

	Sender	Receiver
Cooperative	+	+
Deceptive	+	-
Incidental	- or 0	+
Spiteful	-	-

There are different types of information that can influence animals' behavior.

-Cues: Environmental changes that convey information. For example, decreasing day length is a cue that indicates the approach of winter.

-Signals: Behavioral acts from other animals that convey information.

 Signals can be further divided into two types (this is where it is most important to avoid thinking in terms of consciousness or intention in the communicating animals).

-Incidental signals (see above) are behavioral acts of the sender that benefit the receiver. They do not involve special behavior on the part of the sender.

-Displays: Signals that have been modified by natural selection to enhance their function in information transfer. Displays are special, communicative behavior on the part of the sender.

Ritualization is the process of the evolution of displays from incidental signals. Often, displays originate as incidental signals that become enhanced (by including modifiers), exaggerated, stereotyped, or repeated.

Displays tend to be highly species-typical, but there can also be convergence of displays among distantly related species.

 There are several situations where effective information transfer is very important to the sender. Displays often evolve for use in these situations.

-Sexual. Includes advertising/mate attraction, courtship, pair bonding.

-Agonistic/Aggression. Includes territoriality and maintaining spacing, same-sex competition for mates, dominance hierarchies in highly social species.

-Anti-predator.

 In highly social animals (for example, group-living species) signals are very important for group cohesion and coordination. The number of signals possessed by different species appears to have increased over evolutionary time (although there is a great deal of overlap):

Solitary insect < 10 Social insect 10-20

Fish 10-25 Birds 15-30

Mammals 15-35 Rhesus monkey 37

Information is made up of different forms of energy. Examples of some energy forms used in communication include chemical energy (smell/taste), mechanical energy (vibration- sound), and light energy (visual). A form of energy that can be detected by a single sense organ is called a sensory modality.

Sensory modalities vary in signal quality, and different modalities are suited to different situations.

	Effective distance	Accuracy of direction	Speed of travel	Complexity	Duration
Odor	+ or -	-	-	-	+ or -
Sound	+	0	0	+	-
Touch	-	+	+	-	-
Vision	0	+	+	+	+ or -
Electric	-	+	+	0	-

Species vary in their "sensory modality space".

A final note on signal honesty: Why not cheat?