Aggressiveness in the domestic fowl: Distance versus 'attitude'

It has been suggested that invasion of the personal space by flock members is the main trigger of aggressive interactions in the domestic fowl (Gallus gallus domesticus). In large and dense groups of birds high frequency of attacks should be expected as the chances of invading the personal space of others is likely to occur. However, other studies suggest that after surpassing a certain group size the frequency of aggressive interactions decline. It is possible that the behaviour of the individuals themselves may be more relevant in this context. To test this hypothesis we analysed the onset of aggressive interactions in a laying strain of domestic fowl from videotaped behavioural sequences. A total of 60 interactions were analysed, for which we recorded the location (XY coordinates) of the giver (G) and receiver (R) of an aggression, the position of the two closest individuals to G (G1, G2) and to R (R1, R2), in addition to the behaviour and head orientation of all these birds with the software Chickitizer®. Distances between pairs of birds were calculated as Euclidean distances and analysed by mixed model ANOVA. Behaviours were ordered by ranges of activity and differences analysed by Kruskal-Wallis. Our results indicate that inter-individual distances at the onset of an aggressive interaction varied according to the specific pair of individuals, but contrary to the expected, distances between the G-R remained similar to the distance among the G-G1 and G-G2. R birds however, were consistently involved in more energetic demanding behaviours and with their head oriented towards G. These results suggest that aggression in the domestic fowl does not depend on the invasion of the critical distance per se, but would greatly depend on the activity level and directionality of the individuals which would be perceived as a threat by the aggressor.