Abstract

<jats:p>
There are many secondary metabolites in ripe fruit that are toxic to
vertebrate consumers. The most prevalent explanation for their presence in
ripe fruit is to protect the fruit against consumers that do not disperse
viable seeds. It has been hypothesised that seed dispersers are not deterred
by, or can tolerate, the consumption of secondary metabolites in ripe fruit.
We tested whether silvereyes (Zosterops lateralis),
which are known seed dispersers, were deterred by quebracho (condensed
tannins) presented in two different food types. In the first experiment,
silvereyes were given artificial fruit containing either 0% or
5% quebracho and their fruit consumption was measured. A second
experiment recorded consumption of a cereal-based, long-term maintenance diet
containing either 0% or 5% quebracho. Silvereyes did not exhibit
a significant preference for artificial fruit that did not contain quebracho:
39.9% of the fruit consumed did contain quebracho. However, silvereyes
strongly avoided the cereal diet containing quebracho, consuming, on average,
only 0.36 g (0.06 g) of cereal per 5 h compared with 17.3 g (0.23 g) of cereal
that did not contain quebracho. We suggest that because the artificial fruit
were swallowed whole by silvereyes, the quebracho may not have been detected
as easily in the time available as it would have been in the aqueous cereal
diet. Consumption of fruit containing secondary metabolites by wild silvereyes
is likely to depend on factors such as food availability, nutrient content of
the fruit and the degree of diet mixing.</jats:p>