ROLE OF HELPERS IN THE SENTINEL BEHAVIOR OF THE FLORIDA SCRUB JAY (APHELOCOMA C COERULESCENS)

Two independently conceived and executed field studies using somewhat different methodologies tested the hypothesis that non-breeding helper s of the Florida scrub jay (Aphelocoma c. coerulescens) contribute imp ortantly to antipredator sentinel behaviour. Specifically, we made fou r predictions: 1. Helpers participate to a non-trivial degree in senti nel behaviour; 2. Breeding pairs with helpers spend less time on senti nel behaviour and hence more time foraging; 3. Breeders with helpers h ave more protected foraging time; and 4. Groups with helpers have grea ter total sentinel time. Results of the two studies agreed on most maj or points and even, in many cases, on minor points and quantitative as pects. Non-breeding adult helper birds participated in sentinel watche s almost as much as breeders in their group. In winter, breeding pairs with one or more helpers decreased their own sentinel time compared w ith that of unassisted pairs. However, in the one study, the concomita ntly increased available foraging time of breeders was no better prote cted by another group member being on sentinel than in the lone pairs. Results of the other study showed a significant increase of protected foraging time for breeding males only. In winter, groups with helpers did not have increased total sentinel time; time was either the same (Study A) or significantly less (Study B). During nesting, breeders wi th helpers did not, decrease their sentinel effort relative to lone pa irs. Instead, groups with helpers had a sentinel for more time. These results are interpreted as indicating that, in winter, sentinel behavi our is more important to antiraptor defense in lone pairs than larger groups. In groups with helpers the mere addition of extra pairs of eye s and ears may render formal sentinel behaviour less necessary, so bre eders can decrease their sentinel time and increase their foraging tim e. During nesting, additional sentinels may be important for increased nest protection. The presence of helpers contributing to predator det ection may thus be an important factor in the better annual survival a nd nesting success of breeders that have helpers (WOOLFENDEN & FITZPAT RICK 1984).