Newly hatched Khaki Campbell ducklings (Anas platyrhynchos domesticus) were initially housed in pairs and subsequently transferred to isolated housing conditions. Subjects living with another bird displayed filial behavior and little aggression upon encountering another duckling in a test arena. In contrast, ducklings housed in isolation exhibited aggressive pecking in addition to filial behavior when another duckling was subsequently encountered. In Experiment 2, ducklings were housed with an imprinting object (i.e., an object that elicits attachment behavior), but they were otherwise isolated from other birds. These subjects displayed little aggression when they were subsequently reunited with a conspecific, indicating that the aggression-precluding effects of social housing are not limited to the particular social stimulus with which the ducklings are housed. In Experiment 3, ducklings were again housed with an imprinting object, but this time the object was behind glass, thereby precluding tactile contact with it. Since these birds also exhibited little aggression when reunited with a conspecific, it is apparent that visual stimulation from an imprinting object is sufficient in itself to preclude subsequent aggression. These findings suggest that stimulation that elicits attachment behavior is the critical factor mediating isolation-induced aggression.Numerous species show increased aggressive tendencies toward conspecifics following a period of social isolation. The effect has been observed with chicks (Beach &

Khaki Campbell ducklings were raised in groups of 10, 6, and 3 subjects for 1 week. When the groups were intact, the birds seldom emitted distress calls. When, however, various numbers of birds were systematically removed from each of the groups, the fewer the number of birds remaining in a given group the greater the number of distress calls. Further, a given number of birds remaining from a large group emitted more distress calls than when the same number of birds remained from a smaller group. Subsequent experiments revealed that neither adding birds to a group nor interchanging birds between groups induced distress calling; hence, the distress calling induced by reduction in group size was not simply a reaction to stimulus change. Finally, when ducklings that had been living in a group of a given size were permitted to live in a larger or smaller group for more than 24 hours, they subsequently reacted to reductions of their new group in the same manner as ducklings that had lived in a group of that size all along. These findings are consistent with naturalistic observations of the reactions of immature precocial birds to changes in the composition of their brood.Laboratory studies of imprinting and attachment have typically focused on dyadic relationships: the interactions between a young animal and its mother (or mother surrogate) or the interactions between two peers. Though there are clear advantages to such an experimental strategy, there are reasons to suspect that this approach causes one to miss much of the richness of an animal's social interactions. In a natural setting a young animal typically interacts both with its mother and with a group of conspecifics. A number of investigators (e.g., Harlow & Harlow, 1969;Lorenz, 1935) have shown that an animal's social and emotional development is affected by numerous social inputs.

Newly hatched Khaki Campbell ducklings (Anas platyrhynchos domesticus) were exposed to a moving object that immediately suppressed distress vocalizations occurring in a novel environment. The static visual and auditory features of this object acquired the ability to suppress distress vocalizations after eight 20-min sessions of exposure to the object in motion. The acquired suppressive properties of these features were found to persist throughout thirty 20-min sessions given over 10 days. During these sessions, the ducklings were continually exposed to the static features in the absence of visual movement. In a second experiment, the ability of these features to serve as reinforcement for a pecking response was shown to persist for up to 56 hr. In one duckling, presentations of the static visual features did not maintain pecking behavior. However, it was shown that pecking responses could be re-instated in this duckling by introducing novel stimuli to the environment.

SYNOPSIS Migraineurs and non‐migraineurs performed a weight judgment task designed to measure stimulus intensity modulation style. The study revealed that migraineurs were more likely than non‐migraineurs to increase their estimate of a weight's heaviness following stimulation with a similar weight. This tendency to increase the perceived intensity of stimuli may be one factor underlying the reported vaso constriction of migraineurs to low or moderate intensity stimuli that elicit vaso dilation in non‐migraineurs. Questionnaire data is also described showing that migraineurs have a generalized preference for activities involving less intense levels of stimulation than those preferred by non‐migraineurs. Implications of these findings for understanding the complex etiology of migraine are discussed.

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