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).