Flock Size and the Organization of Behavioral Sequences in Juncos

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Abstract
The sequential organization of scanning for approaching predators and pecking for food was investigated by analyzing films of yellow-eyed Juncos (J. phaeonotus). The birds were photographed as they fed in small winter flocks in southern Arizona [USA]. For a given group size, the probability that a bird scans after each peck was found to be a constant. This probability decreased as flock size increased. The organization of sequences of scanning and pecking can be depicted as a simple Markov chain where an environmental variable, group size, probabilistically governs the change from pecking to scanning. Flock size influences the frequency distribution of the number of consecutive pecks for food.