Читать книгу The Behavior of Animals - Группа авторов - Страница 80

When a female stickleback enters the territory of a male, she is both an intruder and a potential sex partner. The appropriate response to an intruding conspecific is to attack it; the appropriate response to a sex partner is to lead it to the nest. The male essentially does both; he performs a zigzag dance (see Figure 3.4). He makes a sideways leap followed by a jump in the direction of the female, and this sequence may be repeated many times. Sometimes the sideways leap continues into leading to the nest, and sometimes the jump toward the female ends in attack and biting. Thus, the zigzag dance can be considered a case of successive ambivalence. Ambivalent behavior is behavior that includes motor components belonging to two different behavior systems; in successive ambivalence , these components occur in rapid succession.

A somewhat similar case is provided by the “upright” posture of the herring gull (Larus argentatus; Figure 3.6). This display often occurs during boundary disputes when two neighboring gulls meet at their mutual territory boundary. The bird’s neck is stretched and its bill points down; the carpal joints (wrists) of the wings are raised out of the supporting feathers; the plumage is sleeked. The position of the bill and wings are characteristic of a bird that is about to attack (fighting in this species includes pecking and wing beating the opponent), and the stretched neck and sleeked plumage are characteristic of a frightened bird that is about to flee. Further, actual fighting or fleeing often follows the upright posture. Thus, the upright posture is a behavior pattern that includes motor components belonging to two different behavior systems. Unlike the zigzag dance of the stickleback, however, these components occur simultaneously. The upright posture can be considered a case of simultaneous ambivalence . Figure 3.6 also shows that the upright posture can occur in varying forms. In the “aggressive upright,” components of attack predominate, whereas in the “anxiety upright,” components of fleeing predominate.

Figure 3.6 Upright postures of the herring gull: (a) “aggressive” upright; (b) “intimidated” upright; (c) “anxiety” or “escape” upright. (From Tinbergen 1959).

The simultaneous occurrence of components belonging to different behavior systems greatly increases the number and variety of behavior patterns in a species’ repertoire. A technique called motivation analysis can be used to explore such ambivalent behavior patterns, which include many of the bizarre displays exhibited by many species. In a motivation analysis, one looks at the form of the behavior, the situation in which it occurs, and other behaviors that occur in association with it (Tinbergen 1959). An example is provided by Kruijt’s (1964, p. 61) analysis of “waltzing” by the male junglefowl (Gallus gallus spadiceus), the wild ancestor of the domestic chicken (Figure 3.7).

Figure 3.7 “Waltzing” in a male junglefowl. (From Kruijt 1964).

It is a lateral display: the waltzing bird walks sideways around or toward the opponent. Back and shoulders are held oblique, the inner side (the side nearest the opponent) lower than the outer side. Both wings are lifted out of the supporting feathers; the upper and lower arms are slightly lowered so that the rump becomes visible. Otherwise, the inner wing and upper and lower arm of the outer wing remain folded. The hand of the outer wing is lowered perpendicularly to the ground and pulled forward, its plane near the body. The primaries touch the ground and the outer foot makes scratching or stepping movements through the primaries. Head and neck are held at the level of the back and either in the medial plane or slightly turned toward the opponent. The tail spreads and is turned toward the opponent; breast and belly feathers are often ruffled, especially those of the other side.

Kruijt noted that the side of the bird’s body near the hen expressed many components of escape behavior, whereas the side further from the hen expressed many components of attack behavior. It was “as if the part of the animal which is nearest to the opponent tries to withdraw, whereas the other half, which is further away, tries to approach” (Kruijt 1964, p. 65). He also noted that waltzing was always directed toward a conspecific. Somewhat surprisingly, young males directed waltzing equally to males and females, even though adult males almost always direct it toward females. In about two-thirds of the cases it was performed immediately before, during, or immediately after fighting, and in some of these cases behavior associated with escape was also seen. Thus, on the basis of form, situation, and associated behavior, Kruijt could conclude that waltzing is indeed an ambivalent behavior pattern expressing both attack and escape, with attack predominating. Sexual motivation appears to be unnecessary.

Motivation analysis of many complex courtship displays in both birds and mammals has revealed that they are ambivalent activities very frequently involving primarily the attack and escape systems. Such activities are usually essential for successful courtship and reproduction. This means, as mentioned above, that the sex system by itself is often insufficient for achieving these ends, and illustrates clearly why causal and functional questions need to be kept separate.