The birds displayed preferences among the differ-
ent treatments in all three fruit species, with prefer-
ences varying in degree (but not direction) among the
bird species (Fig. 6.13). Because individual variation
within bird species was not statistically significant,
birds were grouped according to species. Frugivores
preferred ripe and lightly infested fruits over unripe
and heavily infested fruits but did not discriminate
between lightly infested and uninfested ripe fruits.
Birds avoided both unripe and heavily infested fruits,
sampling very small quantities of both, with no sig-
nificant difference between the two. Unripe fruits
were eaten much less often when paired with ripe
or lightly infested fruits, and not at all when paired
with heavily infested fruits. Chestnut-capped Brush-
Finches, Clay-colored Robins, and White-eared
Ground-Sparrows ate significantly more lightly in-
fested fruits when these fruits were paired with ripe
fruits than when lightly infested fruits were paired
with unripe ones.
These responses suggest that fruit-eating birds dis-
criminate between slightly infested fruits and "rot-
ten" fruits, and consume lightly infested fruits as
if they were ripe and uninfested. Strong avoidance
behavior was elicited only with unripe fruits and
heavily infested fruits containing mold, bacteria,
fermentation, and a larger number of infesting pulp-
mining larvae. Discrimination against infested fruits
may be an artifact of microbial infestation rather than
of infestation by pulp miners (Travaset 1993), but
ingestion of ripe infested fruits may provide nutri-
tional benefits.Figure 6.13. Effects of larval infestation on fruit consumption by avian frugivores. Mean consumption (g) of unripe
(u) and ripe, lightly infested (i1) and heavily infested (i2) fruits by Chestnut-capped Brush-Finches, Blue-gray Tanagers,
Clay-colored Robins, and White-eared Ground-Sparrows in pairwise simultaneous choice trials using ripe (open bars)
Citharexylum macradenium, Ardisia palmana, and Acnistus arborescens fruits. For each bird species; n - 6 birds per trial.211 Birds