Other Types of Imprinting

Several other behavior patterns seem to be acquired by an imprinting-like process. Most of these cases have been less studied than filial and sexual imprinting, particularly in a laboratory setting, and hence less is known about the details, for instance, of the timing and duration of the sensitive period, and the degree of stability of the learning in the individual.

The acquisition of some nonsocial ecological preferences seems to be influenced by early learning processes. Such ecological imprinting is illustrated by a recent study on great tits and blue tits. These tits inhabit the same woodland habitat, but differ in the ecological niche they utilize, the larger great tit foraging more on the ground and closer to the tree trunk than do blue tits. In an experiment where these tits were interspecifically cross-fostered, adults ofthese birds chose the ecological niche of their foster species rather than that of their genetic species, even though they possess species-typical adaptations for niche utilization (e.g., bill and feet morphology). There are indications from other species that food-type, habitat, and home area preferences also may be similarly affected. For instance, invertebrate cuttlefish have been shown to visually imprint on their preferred prey type. The development of homing behavior is another remarkable example. Salmons learn olfactory information as juveniles and use those odor memories as adults to home to their natal site for reproduction years later. This has been termed olfactory imprinting, and a similar mechanism for homing has been demonstrated in sea turtles and pigeons.

Parental recognition of the young may also be acquired by an imprinting-like process. This process is atypical in the sense that it occurs during adulthood rather than during the early stages of development. It is of course beneficial for parents to recognize their young so that they can direct care to their own kin. In birds, as in a colony of seabirds, vocalization may be particularly important in this regard. In goats, an olfactory imprinting mechanism may help mothers to recognize their own kin at a very early stage. Development of very early offspring recognition is necessary in herds of goats because kids may lose contact with their mother and may then try to approach other females. A few minutes of contact with a kid may be sufficient for the mother to imprint on it. During this period, the mother may learn the smell of the kid, and label it further by licking. Afterwards, she may only allow such labeled kids to suckle. The high arousal of a female giving birth may facilitate the imprinting on the young. In contrast, altricial birds associate the young hatching in their own nests as their own kin and hence do not need to recognize them individually until they leave the nest. However, there is a cost to the parents when following this simple rule of thumb, namely that the parental imprinting mechanism can be exploited by brood parasites, like cowbirds and cuckoos, dumping eggs into their nest. Parasitic eggs may be recognized and removed, but as soon as they hatch, the parasitic chicks are usually given full support by the foster parents.

Imprinting may also play a role in host choice in certain brood-parasitic species. Some brood-parasitic birds exploit hosts of a particular species, and the egg of the brood parasite has evolved to mimic the host egg. Hence, the brood parasite must recognize its optimal host species, and it has been suggested that they may have imprinted on the host only to such an extent that they prefer exploiting, but not mating with, the same kind of host that they grew up with.

Song learning and song preference learning in oscine birds, sometimes referred to as acoustical imprinting, have been studied in great detail, and possess some of the characteristics of imprinting. However, the sensitive period for song learning occurs later than in the classical cases of imprinting, and the time window for learning may be considerably extended. Also, tutor choice in song learning is often more diverse than is the case in filial and sexual imprinting. There may also be a greater degree of flexibility throughout life in song learning. Language acquisition in humans is an analogy to avian song learning.

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