External factors- 



- Motivation 



/ 



releaser mood 



\ / 



Neural mechanism 



Behavior 



FIG. 2-5 Factors involved in the activation of an instinct. 



hormones or as kinesthesia involving changes in the 

 tension of muscles and tendons or changes in shape 

 or form of muscle fibers. Motivation is established 

 when there is an accumulation of internal stimuli po- 

 tentials as the result of hormone action, kinesthetics, 

 or changes of metabolism. A combination of motiva- 

 tion with proper external conditions and stimuli sets 

 up a drive, such as the hunger drive, or reproduc- 

 tive drive (Richter 1927). 



Once a major drive is initiated, satisfaction of it 

 requires a series of events and stimuli at different 

 levels of integration, so that a hierarchy of drives, ac- 

 tions, and stimuli is established. The significance of 

 this hierarchy is that a major activity in the life cycle 

 of an animal does not take place until the organism 

 is in a proper physiological state, which depends, 

 often in large part, on the environment, and then one 

 action leads to another until consummation is com- 

 pleted. In the male stickleback, for instance, the re- 

 productive drive is not initiated until hormone stimuli 

 are released as the result of gonad enlargement and 

 response to lengthening daily photoperiods. Once the 

 reproductive stimulus is given, the first secondary 



FIRST LEVEL SECOND LEVEL THIRD LEVEL 



drive is the establishment of nesting territories by 

 fighting among male fishes. Then the nest is built. 

 Only after this is completed is the male ready to re- 

 ceive the female. 



Even though an animal may have potential ca- 

 pacities in its sense organs with which to respond to 

 the whole environment, a particular action is trig- 

 gered by stimuli from only a very small part of the 

 environment. This is a fundamental characteristic of 

 innate behavior, and the discovery of these critical 

 sign stimuli or releasers is necessary for an apprecia- 

 tion of the interrelation of animals in a community 

 and how they respond to their environment (Lorenz 

 1935, Tinbergen 1951). 



The complete enactment of mating behavior in 

 the stickleback proceeds step by step in an orderly 

 manner, each action a releaser for the ne.xt. If any 

 one step is changed, or is interrupted, the behavior 

 subsequent in the sequence does not take place. Re- 

 leasers are of a variety of sorts in different species, 

 but commonly involve particular colors or color 

 patterns, call-notes or songs, shapes, chemicals, or 

 contacts, as well as associated acts, positions, or move- 

 ments on the part of another animal. If these trig- 

 gers are not presented, the behavior does not become 

 expressed even though a specific nervous mechanism 

 is present. The analysis of behavior through obser- 

 vation and experimentation with the objective of un- 

 derstanding how an animal acts under natural con- 

 ditions constitutes the science of ethology, an essential 

 branch of ecology. Ethology differs from psychology 

 in that it is concerned with understanding not only 

 the causality of behavior but also the survival value 

 of behavior patterns under natural conditions, and 

 the evolution of these patterns. Psychology is con- 

 cerned more with analyzing the nervous mechanisms 

 that are involved. 



Reproductive [ 

 drive 



• Fighting 



Chasing 



Biting 



Threatening 



Digging 



Testing of materials 



Boring 



Gluing 



Zigzag dance 

 Leading female to nest 

 Showing entrance 

 Quivering 

 Fertilizing eggs 



Fanning 

 Rescuing eggs 



FIG. 2-6 The hierarchy of drives an< 

 sticltleback (after Tinbergen 1951). 



Learning 



All behavior is not, of course, automatic and 

 inherited. Much of it represents the adjustment of 

 fixed patterns to changes in and conditions of the 

 animal's surroundings (Thorpe 1956). Learning may 

 be defined as the adaptive change in individual be- 

 havior as a result of experience. 



The simplest form of learning is habituation, that 

 is, learning not to respond to stimuli which tend to 

 be without significance in the life of the organism. 

 Young animals, for instance, have an innate tendency 

 to respond to a wide variety of danger stimuli, such 

 as any sudden movement or noise. However, when 

 such stimuli are presented repeatedly without asso- 

 ciation with further effects, the young animal learns 

 to disregard them. There is some evidence, on the 

 other hand, that instinctive recognition of a special- 



1 4 Background 



