Displacement grooming in the chaffinch

Abstract

An attempt is made to explain displacement grooming in approach-avoidance conflict situations on the assumption that grooming is a response to peripheral stimulation. Local and general increases in peripheral stimulations produce specific and general increases in grooming in conflict and non-conflict situations. It is concluded that frequency and composition of grooming in conflict situations are initially determined by intensity and pattern on peripheral stimulation. However, this grooming is further regulated by the opportunity to respond to the stimulation. This can be subdivided into two parts: 1. 1. A suitable state of motivation with respect to other activities. This is shown statistically to correlate with equal tendency to perform both the actions of the primary conflict. This is called the equilibrium state. 2. 2. Duration of the equilibrium state—i.e. adequate time at equilibrium to perform the grooming response. Thus when stimulation is constant in conflict situations, probability of grooming is directly proportional to the average length of visit at any point; thus the controlling factor is the probability of interruption. The different grooming actions are associated with pauses of different lengths, the components of which are analysed; the lengthiest types are most susceptible to interruption, and are therefore least frequent where visits are shortest. There is thus a “mechanical” effect on the composition of grooming, independent of the initial pattern of peripheral stimulation. There is a minimum length of time in which grooming can occur, which varies with different types of grooming, but which is always longer than the actual motor pattern. It is concluded that it is necessary for the bird to remain in the equilibrium state for a certain period before grooming commences. It is possible during this time that the peripheral stimulation which produces grooming is perceived. As interruption is the main controlling factor of displacement grooming, it is considered that this explains the incomplete and “frantic” performance which is often characteristic. The effect of different intensities of conflict upon the grooming performance is examined. Grooming performance differs in the different conditions, but the differences are only those which could be expected from the direct effect of the increase in conflict on the incidence of activities other than grooming. When these are compensated for mathematically, the grooming performances do not differ significantly. The results are discussed in the light of theories of motivation of displacement activity. No evidence for the “surplus” hypothesis has been found. It is confirmed that disinhibition of grooming takes place at equilibrium in conflict situations, but the further control of frequency and composition is due to the factors described, not the degree of disinhibition.