Calls

Calls are vocalizations considered simple, stereotypical, largely independent of vocal experience for their development, and usually produced by both males and females during the

Figure 10.15 Song sonograms of the rufous-collared sparrow (Zonotrichia capensis). The initial part of the song includes 2—4 relatively long elements in these samples and is called the theme. The ending portion of the song includes a variable number of fast notes and is called the trill. These sonograms were recorded in different regions of Argentina: (A) and (C) were recorded in forested habitats, southwest of the Pampas region, whereas (B) comes from a male living in the highland grasslands of Cordoba, in central Argentina. Differences in trill structure reflect geographic variations in the song, called dialects.

Source: Photo courtesy of Pablo Tubaro.

entire year. Calls tend to be unimpaired by deafening after hatching, suggesting that they develop normally even in the absence of auditory feedback (Konishi, 1963). However, research also shows that the context in which some of these calls occur depends on experience. For example, chickens emit alarm calls advertising the presence of a predator in the vicinity, but the frequency of these alarm calls depends on the type of audience. Male chickens (Gallus gallus) emitted more alarm calls when surrounded by conspecifics than by bobwhite quail (Coliuus virgin ¡aims), whether the conspecifics were mates, other females, or chicks. The frequency of calls was also very low when the animals were alone in the test arena (Karakashian, Gyger, & Marler, 1988).

In some precocial species, different calls are elicited by different food items. For example, the food calls of chickens (Gallus gallus) convey information about the quality of the food (Marler, Dufty, & Pickert, 1986). A hen’s food call attracts her chicks to food sources, and a cock’s food call attracts hens to his vicinity, increasing courtship opportunities. In the laboratory, high-quality food calls can be released by providing a mealworm, whereas the low-quality calls can be induced by providing regular laboratory food. The two calls involve the same note, but the note is repeated at a higher frequency in the high-quality call.

In some species, food calls can control behavior even before they are associated with higher low-quality food items. Calls are therefore said to be prefunctionally organized (Moffatt & Hogan, 1992). In one experiment, two groups of Burmese red junglefowl chicks (Gallus gallns spadiceus) received instrumental training in a runway, where they were exposed to two kinds of trials in a random order. In one group, running when the high-quality food call (signal) was being played back through a speaker was reinforced with a mealworm (reward), whereas running when the low-quality food call was being presented was nonreinforced. In this condition, the signal matched the quality of the reward, and chicks rapidly learned to run faster in the presence of the high-quality food call. In the reverse condition, the low-quality food call was the signal for a mealworm reward, whereas the high-quality call was paired with nonreinforcement. The speed of running was initially higher for the high-quality call than for the low-quality call, but as training progressed, chicks ran faster in the presence of the low-quality call signaling a mealworm. While chicks tend to respond faster to the high-quality food call, this tendency can be reversed by experience.

Maternal calls are also attractive to chicks of several precocial species soon after hatching. These vocalizations are referred to as assembly calls because the young birds respond by approaching the source of acoustic stimulation. Experiments with Peking ducks (/bras platy-rhynchos) have uncovered the importance of auditory embryonic experience in the development of such preference (Gottlieb, 1981). To exhibit preference for the distinctive maternal call, duckling embryos must be exposed to their own vocalizations and those of their broodmates during prehatching development in the nest. The calls emitted by one embryo can be heard both by that embryo inside the egg as well as by other embryos in adjacent eggs. The importance of these sources of experience was demonstrated by a combination of devocalization, deafening, and individual incubation. When embryonic acoustic experience is prevented, ducklings respond to the maternal calls of several species. Interestingly, the embryonic calls that are so important in this process bear little overall resemblance to the assembly call emitted by the hen, containing only isolated features in common (e.g., the range of frequencies, or notes per second, is similar). Moreover, this experience must occur before hatching to be effective, suggesting the presence of a sensitive period (Gotdieb, 1985).

Calls can be simple and stereotypical, but they are quite malleable. Calls can control behavior acting as discriminative stimuli and require prehatching experience to develop their species-typical form.