Sequential predictability of the scanning behaviour of greater rheas, Rhea americana

CARRO, MARIANA; FERNÁNDEZ, G.J.; REBOREDA, J.C.

ETHOLOGY ECOLOGY & EVOLUTION

UNIVERSITA DEGLI STUDI DI FIRENZE

Año: 2011 vol. 23 p. 27 - 39

0394-9370

Some models that predict the scanning pattern to maximize the probability of predator detection by preys assume sequential randomness (i.e. length of inter-scans intervals are independent from each other and from the length of scan events). Sequential randomness would avoid that stalking predators synchronize their attacks with long inter-scan intervals. We analyzed the presence of sequential randomness in the scanning behaviour of the greater rhea (Rhea americana), a large flightless bird that forages solitarily or in groups. We analyzed sequences of behaviour of 40 wild rheas, foraging solitarily or in groups of 2 to 17 individuals, in two populations of eastern Argentina. We used parametric (auto and cross-correlations) and non-parametric (Runs tests and Spearman Rank Correlations) tests to detect dependence among intervals. We detected temporal dependence of inter-scan intervals in 30 of 40 behavioural series, but only 11 of 40 sequences showed consistent dependence when tested using parametric and non-parametric tests. The temporal dependence detected in some individual sequences would still be used by predators to synchronize their attacks with long inattentive periods of the preys. However, simple simulations showed that attack success would not be different from that of predators launching their attacks at the beginning of a randomly selected inattentive period of the preys. We propose that temporal dependence in greater rheas would be the result of simple mechanistic rules determined by the compromise between foraging and scanning behaviour and it would be of scarce value to potential stalking predators.