Food Caching Behavior in Pikas
Studies in ontogeny attempt to explain changes in a behavior across the lifespan of an organism in terms of development. These explanations are generally concerned with the degree to which a behavior can be changed through learning.
Ontogeny of Food Caching
Breeding and maternal care
Pikas breed in April and June of each year with pregnancy lasting around 4 weeks. During breeding season, male pikas enlarge their territories to overlap with the female territories closest to them (Connor and Whitworth 1985). Juveniles are born blind but with fully emerged teeth. They have a range of juvenile-specific vocalizations related to nursing, distress, and panic (Connor and Whitworth 1985). The pikas can leave their nest after around one week. Once the young pikas are old enough to forage, they are allowed to do so alongside their mother only until approximately their fifth week of age. Maternal care ceases completely after the fifth or sixth week. At this point, it is important for the juveniles to acquire feeding territories that will allow them to forage and cache food for their first winter (Golian and Whitworth 1985).This territorial feeding and caching behavior is an adaptation that allows the pikas to survive winter food shortages.
Competition for Food begins at an early age
The main factor driving the dispersal of pikas across a habitat is competition for these feeding territories. Intraspecific competition begins during development at just two weeks of age when the larger, more aggressive male juveniles begin to outcompete their female siblings for nursing positions. Despite being less aggressive, female pikas are actually significantly larger at birth than their male siblings. The average male size is not significantly larger than the females until they reach their adult weight at 12 to 14 weeks of age, long after dominance hierarchies are already established. However, the most dominant young are also observed to be the largest at that point (Whitworth and Southwick 1981, Whitworth and Southwick 1984).
Little parental care is provided by mothers outside of nursing and resting, and no play or social behavior is observed among littermates. By the end of the maternal care period, all interactions between littermates and their mother are agonistic. At this point, all of the young are observed to show dominance over the mother pika, and all male young are dominant over their female siblings. Because pikas are territorial, the young, less agonistic females must disperse farther than the males to find foraging grounds. A higher birth rate has been observed for female pikas which may serve to balance out female mortality due to dispersal distances and competition with males for food (Whitworth and Southwick 1984).
Development and Learning
The development of foraging and caching behaviors in pikas has not been studied. However, in other food caching animals such as hamsters, the behavior is observed in the early stages of development (Smith and Reichman 1984). This indicates that the behavior is innate rather than learned. Pikas are sometimes allowed to forage alongside their mothers and littermates for a short time after they are weaned, but it is not clear whether the behavior is learned in this way through imitation or if the offspring's behavior can be altered in any way by the foraging and caching behaviors of the mother.