Group size effects on vigilance: we need more bricks in the wall

Research on the effects of group size on vigilance have widely attracted the attention of investigators in the last decade. Generally, it has been established that an increase in group size produces a decrease in vigilance level (see [Beauchamp, 2003]). However, some exceptions to such inverse an relationship have been shown (see [Beauchamp, 2003 and Barbosa, 2002]). Behavioural and ecological patterns and processes are not simple and the relationship between group size and vigilance is not an exception as the review made by [Beauchamp, 2003] points out. Beauchamp’s review clearly shows the problems which are affecting the understanding of group size effect on vigilance level. There are at least three factors affecting vigilance, such as predation, competition through interference and scrounging. Group size effect on vigilance varies depending on factor combinations. How the combination of these factors varies depending on intrinsic and extrinsic factors and how such variation affects group size effect, have been studied little. For instance, one intrinsic factor, determined by physiological and/or morphological characteristics, is the capacity of some species to be vigilant while foraging with the head down ( [Lima and Bednekoff, 1999]) or with the head up during handling ( [Beauchamp and Livoreil, 1997. G. Beauchamp and B. Livoreil, The effect of group size on vigilance and feeding rate in spice finches (Lonchura punctulata). Can. J. Zool. 75 (1997), pp. 1526–1531. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (36)Beauchamp and Livoreil, 1997]) or during searching for food ( [Barbosa, 1995]). This capacity could be linked with differences in foraging strategy which has been showed to influence flocking and scanning behaviour at both interspecific and intraspecific level, as well as the group size effect on vigilance, at least in waders ( [Barbosa, 1995, Barbosa, 1997 and Barbosa, 2002]).

Peer reviewed