René Zayan

An Experimental-model of Aggressive Dominance in Xiphophorus-helleri (pisces, Poeciliidae)

An experimental model was constructed using seven postulates derived from the experimental results of Zayan (1974, 1975a,b,c, 1976). The model specifies the relative importance of several asymmetries in predicting aggressive dominance in Xiphophorus helleri . These asymmetries concern difference between duellists with respect to: prior residence in the tested area (vs intrusion); immediate social experiences of dominance or submission; social isolation; individual familiarity and recognition. The predictions of the general model were checked experimentally and confirmed; a multiple orthogonal regression accounted for about 97% of the variance in our experimental results. The basic experimental results serving as postulates were confirmed and could be generalized; a new synthetic and predictive model was formulated concerning the determinants of aggressive dominance in Xiphophorus .

Categories as paradigms for comparative cognition

Forming categories is a basic cognitive operation allowing animals to attain concepts, i.e. to represent various classes of objects, natural or artificial, physical or social. Categories can also be formed about the relations holding among these objects, notably similarity and identity. Some of the cognitive processes involved in categorisation will be enumerated. Also, special reference will be made to a much neglected area of research, that of social representations. Here, animals conceive the natural class of their conspecifics as well as the relationships established between them in groups. Two types of social categories were mentioned: (1) intraspecies recognition including recognition of individual conspecifics; and (2) representation of dominance hierarchies and of their transitivity in linear orders.

Mental representations in the recognition of conspecific individuals

Individual recognition requires that animals form mental representations of the properties of conspecifics as well as of the identity of particular conspecifics. Gallistel has defined representations as a precise correspondence (an isomorphism) between objects and relations in the environment and structure-preserving systems in the animals brain. Research on the neural recognition of individual conspecifics is examined to check whether the results satisfy part of Gallistels definition. Mental representations are also discussed with reference to concept-discrimination experiments which have demonstrated individual recognition using slides of conspecifics. Finally, a simple set-theoretical model is presented to describe recognition of the idiosyncratic properties of conspecifics.

Observations on pushing and aggression in pairs of hens in battery cages

An experiment was designed to test in two strains of chickens whether aggression and pushing behaviour in pairs of hens depended on the amount of available space in battery cages. There was essentially no aggression and cage areas had no effect on the frequency of aggressive pecks. Pushing behaviour (which was reciprocal) was often observed in the battery cages, but its frequency was not affected by density. Most results were similar for the 2 strains. Post-experimental observations confirmed these results. Feather-pecking was largely absent in pairs of the light strain whereas it was significantly affected by floor area in pairs of the medium strain, i.e. most frequent at intermediate cage areas. Inter-cage aggressive pecks were significantly more frequent than intra-cage ones.

Responsiveness to “social” releasers in cattle. I. A study of the differential and additive effects of visual and sound stimuli, with special reference to the law of heterogeneous summation

Two experiments (Exp.1, Exp.2) were carried out to investigate the effects of social releasers, i.e. models and calls of conspecifics, on the approach responses of Friesian-Dutch heifers. In Exp.1, models consisted of either a vague representation of a conspecifics shape, or of a life-sized photograph of a conspecific. Sound (S) stimulations (calls) and movement (M) were combined to these visual (V) models. In Exp.2, V models and S stimulations were presented either separately or in combination. Models consisted of a ♂ and of a ♀ life-sized photograph and S stimulations consisted of recorded calls of ♂♂ or of ♀♀ conspecifics. In Exp.1, a significant increase in responsiveness was found after addition of sound S to the V models, especially to the photographs. Adding S to V models resulted in a much higher increase in responsiveness than adding M to V models. An additive effect was also found in Exp.2: combined presentations of V and S increased significantly the number of responses and of responding subjects as compared to either V or S separate presentations. In both Exp.1 and Exp.2, the total number of responses was a little more than twice as high for combined presentation of V and S as it was for V separate presentations, or for S separate presentations (Exp.2). In Exp.2, a complete verification of Seitzs law of heterogeneous summation of the stimuli was attempted by a further comparison, demonstrating that the releasing effect of V and S presented in combination (simultaneously) was equivalent to the number of responses found after addition of the partial effects of V and S presented separately (successively).

Responsiveness to "social" releasers in cattle. II. Relation between social status and responsiveness, and possible effect of previous familiarization with the test conditions.

The data of two previous experiments, investigating the effects of social releasers in Friesian-Dutch heifers were analysed in order to verify whether the frequency of approach responses to models and calls of conspecifics was modified by pre-experimental factors. First, responsiveness was correlated to the social status of individuals; a social hierarchy was assessed on the basis of agonistic interactions recorded for a 2-month period prior to the experiments with models. A significant positive correlation was found between the total number of responses and the total number of escape-avoidance reactions to aggressive acts. The same result was found when individual ranks were assessed on a hierarchy re-presenting a dominance order established on the basis of the number of aggressive acts causing escape-avoidance reactions. In this case, also, animals with highest ranks presented a significantly higher number of responses to models than animals with lowest ranks. In our second experiment, a significant positive correlation was found between all criteria used to assess individual ranks in a hierarchy, while this result was not found necessarily in the first experiment. The other pre-experimental factor under consideration was a possible familiarization with the testing conditions (models/calls of conspecifics, handling, and other procedures); some of the group-members tested during the second experiment had already been tested in the first one, carried out a year before. Many results demonstrated that the frequency of responses to social releasers was significantly lower for the previously tested subjects than for the animals tested for the first time.

Measures of space in pairs of hens in battery cages

An experiment was designed to test whether distances between 2 hens depend on the amount of available space in a cage. Interindividual distances were recorded as well as contact behaviour since it represents the most extreme reduction of interindividual distance. Pairs of hens from 2 strains (Rhode Island Red x White Plymouth and White Leghorn) were observed in cages of a battery-like system. The experimental schedule was: 1 week at initial densities; 10 weeks at changing densities; 1 week at final densities which were identical to the initial ones. The initial conditions were Small (900 cm(2)/bird), Medium (1400 cm(2)/bird) and Large (1900 cm(2) /bird). Each of these conditions was gradually changed to two intermediate conditions by means of successive weekly density increases or decreases (100 cm(2)/ bird) for 5 weeks: thereafter, the final densities were restored by successive weekly decreases or increases. The intermediate conditions were: Very Small (400 cm(2)/bird) or Medium (1400 cm(2)/bird) for small cages; Small (900 cm(2)/bird) or Large (1900 cm(2)/bird) for medium cages and Medium (1400 cm(2)/bird) or Very Large (2400 cm(2)/bird) for large cages. It was found that the larger the cages, the larger were the interindividual distances. Thus, it is the objective space which determines the occupation of a cage; hens do not use all the available space in their cage at any density. Contact behaviour was more frequent in the smaller the cages. The results are discussed in the context of welfare with regard to the minimum space required by laying hens in battery cages. Recommendations are made on the basis of the average distances which were recorded in all the experimental conditions.