Conspecific agonistic behaviour in the Mediterranean parrotfish

Abstract

Aggressive behaviour in fishes, particularly in territorial species, is a common trait used to defend resources such as food or mates. Territorial males of the Mediterranean parrotfish Sparisoma cretense have been described to chase away conspecifics yet other aggressive behaviour repertoire has not been reported for this species. We describe, for the first time, an extreme aggressive behaviour between two male Mediterranean parrotfish which includes biting and prolonged mouth locking.

Eastern gray squirrel (Sciurus carolinensis) color morphs do not differ in aggressiveness

Abstract

Eastern gray squirrels (Sciurus carolinensis) exhibit a variety of color morphs, including black. In the USA and UK, a common folk belief is that black squirrels are more aggressive than squirrels of other colors. We tested the biological basis of that belief using data from the 2018 Central Park squirrel census. Contrary to the belief, black squirrels do not chase other squirrels more often than do conspecifics of other colors. Black and non-black squirrels were equally likely to approach people for food and to display indifference to human presence, but black squirrels were more likely than non-black squirrels to flee from people. Although other research has found that aggression among squirrels increases when they live in higher population densities, black squirrels were no more aggressive than non-black squirrels despite the fact that they were sighted in parts of Central Park with higher squirrel population densities than other locations.

Kea (Nestor notabilis) show flexibility and individuality in within-session reversal learning tasks

Abstract

The midsession reversal paradigm confronts an animal with a two-choice discrimination task where the reward contingencies are reversed at the midpoint of the session. Species react to the reversal with either win-stay/lose-shift, using local information of reinforcement, or reversal estimation, using global information, e.g. time, to estimate the point of reversal. Besides pigeons, only mammalian species were tested in this paradigm so far and analyses were conducted on pooled data, not considering possible individually different responses. We tested twelve kea parrots with a 40-trial midsession reversal test and additional shifted reversal tests with a variable point of reversal. Birds were tested in two groups on a touchscreen, with the discrimination task having either only visual or additional spatial information. We used Generalized Linear Mixed Models to control for individual differences when analysing the data. Our results demonstrate that kea can use win-stay/lose-shift independently of local information. The predictors group, session, and trial number as well as their interactions had a significant influence on the response. Furthermore, we discovered notable individual differences not only between birds but also between sessions of individual birds, including the ability to quite accurately estimate the reversal position in alternation to win-stay/lose-shift. Our findings of the kea’s quick and flexible responses contribute to the knowledge of diversity in avian cognitive abilities and emphasize the need to consider individuality as well as the limitation of pooling the data when analysing midsession reversal data.

The effect of dimensional reinforcement prediction on discrimination of compound visual stimuli by pigeons

Abstract

We trained eight pigeons (Columba livia) on a stagewise go/no-go visual discrimination task. A total of 16 visual stimuli were created from all possible combinations of four binary dimensions: brightness (dark/bright), size (large/small), line orientation (vertical/horizontal), and shape (circle/square). In the first stage, we presented S + and four S– stimuli: sharing one (brightness), two (brightness and orientation), three (brightness, orientation, and size), or no dimensional values with S + . In the second stage, all 16 stimuli were presented. In the first stage, stimulus discrimination was controlled by the number of dimensional disparities between non-rewarded stimuli and a rewarded one rather than by stimulus dimensional salience, whereas at the beginning of the second stage, pigeon behaviour was controlled mainly by dimensional reinforcement expectancy learned in the first stage. At the beginning of the second stage, pigeons correctly rejected 6–8 of 11 new added S- stimuli. A significant inverse correlation between the number of S– stimuli sharing dimension values with S + in the first stage and the dimensional discrimination ratios at the beginning of the second stage was found.