Predation risk and vigilance in the blue tit (Parus caeruleus)

Abstract

Feeding blue tits (Parus caeruleus) increase their scanning rates as predation risk increases. However scan durations remain constant. As risk increases the frequency distribution of inter-scan intervals shifts from a regular (rectangular) to a random (exponential) distribution with a 0.5 s constraint on the minimum inter-scan interval. Cine analysis reveals that this 0.5 s constraint represents the minimum time needed to extract a piece of peanut from a feeder (the 'handling time constraint'). Manipulating handling times by grinding peanuts to smaller sizes allows tits to adopt random scanning patterns. © 1983 Springer-Verlag.