Читать книгу The Behavior of Animals - Группа авторов - Страница 32

Sign-stimuli can be simple, such as vibration or bodily touch, suitable to elicit escape in a crayfish, or more complex. For example, configurational stimuli are determined by several features. Depending on the way features are related to each other, Tinbergen (1951) distinguished a static configuration (involving spatial relationships) from a dynamic configuration (involving spatiotemporal relationships, such as motion).

An example of static configuration is the sign-stimulus eliciting gaping in nestling thrushes, Turdus merula, toward the parent. In experiments using dummies (Figure 2.3b), the parent was modeled by two solid disks of different diameters, the large one simulating its rump r, the smaller one its head h. Nestlings aimed at the head, if the head-to-rump ratio was 1:3. This was examined with a “two-head-rump” model giving nestlings a choice between a head in 1:2 ratio and an adjacent one in 1:3 (Tinbergen & Kuenen 1939; cit. Tinbergen 1951). Hence h and r are features; their spatial arrangement yields the configuration. Its recognition is invariant to a change in other stimulus parameters, e.g., in size—within limits—provided the 1:3 ratio is preserved. Although movement improved the efficacy, the spatial relationship between head and rump turned out to be the prominent sign.

An example of dynamic configuration concerns the goose/hawk discrimination. Tinbergen (1951) showed that a bird model (Figure 2.3c) elicited escape in young turkeys, Gallopavo meleagris, when the model was flown overhead with the short end and the wings leading, simulating the silhouette of an airborne bird of prey. But the same model flown with the long end leading, resembling a harmless goose-like bird, was ignored. Subsequent research has shown that this configurational discrimination resulted from stimulus-specific habituation discussed later in this chapter.