We examined spontaneous quantity discrimination in untrained domestic cats in three food choice experiments. In Experiment 1, we presented the cats with two different quantities of food in eight numerical combinations. Overall, the subjects chose the larger quantity more often than the smaller one, and significantly so when the ratio between the quantities was less than 0.5. In Experiment 2, we presented the cats with two pieces of food in four different size combinations. Again, subjects chose the larger piece above chance, although not in the combination where the largest item was presented. In Experiment 3, a subset of the cats was presented multiple times with two different quantities of food, which were hidden from view. In this case, the cats did not choose the larger quantity more often than the smaller one, suggesting that in the present experiments they mainly used visual cues when comparing quantities. We conclude that domestic cats are capable of spontaneously discriminating quantities when faced with different numbers or sizes of food items, and we suggest why they may not always be motivated to choose the larger quantity. In doing so, we highlight the advantages of testing spontaneous choice behavior, which is more likely to reflect animals' everyday manner of responding than is the case when training them in order to test their absolute limits of performance which may not always coincide with their daily needs.

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Consistent inter-individual differences in behaviour have been previously reported in adult shelter cats. In this study, we aimed to assess whether repeatable individual differences in behaviours exhibited by shelter cats in different situations were interrelated, forming behavioural syndromes. We tested 31 adult cats in five different behavioural tests, repeated three times each: a struggle test where an experimenter restrained the cat, a separation/confinement test where the cat spent 2 min in a pet carrier, a mouse test where the cat was presented with a live mouse in a jar, and two tests where the cat reacted to an unfamiliar human who remained either passive or actively approached the cat. Individual differences in behaviour were consistent (repeatable) across repeated trials for each of the tests. We also found associations between some of the behaviours shown in the different tests, several of which appeared to be due to differences in human-oriented behaviours. This study is the first to assess the presence of behavioural syndromes using repeated behavioural tests in different situations common in the daily life of a cat, and which may prove useful in improving the match between prospective owner and cat in shelter adoption programmes.

The comparative study of the perception of visual illusions between different species is increasingly recognized as a useful noninvasive tool to better understand visual perception and its underlying mechanisms and evolution. The aim of the present study was to test whether the domestic cat is susceptible to the Delboeuf illusion in a manner similar to other mammalian species studied to date. For comparative reasons, we followed the methods used to test other mammals in which the animals were tested in a 2-way choice task between same-size food stimuli presented on different-size plates. In 2 different control conditions, overall the 18 cats tested spontaneously chose more often the larger amount of food, although at the individual level, they showed interindividual differences. In the Delboeuf illusion condition, where 2 equal amounts of food were presented on different-size plates, all cats chose the food presented on the smaller plate more often than on the larger one, suggesting that they were susceptible to the illusion at the group level, although at the individual level none of them performed significantly above chance. As we found no correlation between the cats’ overall performance in the control conditions and their performance in the illusion condition, we propose that the mechanisms underlying spontaneous size discrimination and illusion perception might be different. In the discussion, we compare the results of the present study with the results for other previously tested mammals and highlight some possible reasons for their similarities and differences.

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