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| To maximize fitness, many animals must trade
off their need to forage efficiently against their need to
avoid predators. We studied such a trade-off in four species
of tits (Paridae) in a forest near Oxford, UK. During
winter, tits form flocks which increase feeding efficiency
and reduce predation risk. These flocks feed extensively
on beech (Fagus sylvatica) seeds, the abundance of
which may be critical for winter survival. Because these
seeds drop to the ground, where birds are exposed to
sparrowhawk (Accipiter nisus) attack, tits need to trade
off their need to find seeds against the proximity to protective
cover, provided by dense clusters of hawthorn
(Crataegus spp.). The quality of the beech crop differs
markedly between trees and years. During a year of
abundant beechmast, most tits searched for seeds close
to protective cover. This ‘safety-first’ strategy precluded
visits to superabundant food patches if they were too far
from protective cover. Among beech trees near to cover,
tits tended to prefer those with high seed density. Tits
benefited from foraging under trees with high seed density
because this correlated significantly with seed mass
per square metre and because mean search times decreased
with increasing seed density. Finally, we show
experimentally that great tits, Parus major, can discriminate
between edible (viable) and inedible (empty) seeds. | |
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