habitats (Greenberg and Gradwohl 1980, Remsen and
Parker 1984, Winnett-Murray 1986). Their young may
depend on longer periods of time spent foraging with
their parents more than other wrens, as they learn to
recognize and capture highly cryptic prey (Fogden
1972, Morse 1980).
Acknowledgments Many members of the Monte-
verde community kindly allowed me to study wrens
on their land, and the Tropical Science Center granted
permission to study wrens in the MCFP. The Univer-
sity of Florida, Sigma Xi, the Chapman Fund of the
American Museum of Natural History, and the Jessie
Smith Noyes Foundation of the Organization for Tropi-
cal Studies provided financial support. Alexander
Villegas and Sarah Sargent assisted with fieldwork,
and Bruce Young and Greg Murray provided edito-
rial assistance.Figure 6.12. Frequency distribution of the types of prey
wrens brought to their nestlings. Prey type categories are
(1) arachnids, (2) adult lepidopterans, (3) larvae, (4)
dipterans, (5) hymenopterans, (6) homopteransand
hemipterans, (7) orthopterans, and (8) coleopterans.
Sample sizes of prey items were as follows: Gray-breasted
Wood-Wrens (GW; 30), House Wrens (HW; 464), Plain
Wrens (PW; 22), and Rufous-and-white Wrens (RW; 22).
DO FRUIT-EATING BIRDS ACTIVELY SELECT OR
AVOID INSECT-INFESTED FRUITS?
Lisa 1C Valburgrait-eating birds in Monteverde have a bounti-
ful smorgasbord of fruits from which to choose
(Wheelwright et al. 1984), Much research has
been done to discover what makes a fruit desirable
or undesirable. Birds can distinguish among fruits of
the same species based on sugar content, flavor, ripe-
ness, color, seediness, and other factors (Fleming and
Estrada 1993). However, even highly frugivorous birds
such as Common Bush-Tanagers may consume insects
for as much as 50% of their regular diet (Valburg
1992c).
Tropical plants that bear bird-dispersed fruit are
often infested with insect larvae. Some researchers
have suggested that infestation should cause rejection
by frugivores (Sallabanks and Courtney 1992). How-
ever, not all infestation results in the same type or
level of damage to seeds, and fruit damage may not
always affect palatability (L. Valburg, unpubl. data).
I examined whether the presence of insect larvae
caused a fruit to be preferentially chosen or avoided
by Common Bush-Tanagers. I captured 10 bush-
tanagers and, after the birds became accustomed to
their aviary cages, offered them simultaneous dichoto-
mous choices between naturally infested and unin-
fested fruits of a single species. The presence of in-
sect larvae enhanced the rate of fruit removal for three
species of fruits, especially Acnistus arborescens and
Ardisia palmana (Valburg 1992b).
I then investigated how different levels of infesta-
tion by pulp-mining insect larvae combined with dif-
ferent levels of fruit ripeness might influence fruit
choice in four other bird species. Fruits were collected
from at least 10 plants per species within Monteverde,
Cerro Piano, and Santa Elena. I conducted simulta-
neous choice trials using four individuals of each of
the following species: Clay-colored Robins, Blue-gray
Tanagers, Chestnut-capped Brush-Finches, and White-
eared Ground-Sparrows. The birds were offered three
fruit species: Citharexylum donnell-smithii, Ardisia
palmana, and Acnistus arborescens. Fruits were pre-
sented in equal masses in pairwise combinations of
ripe (uninfested), unripe, and two levels of infesta-
tion, light (1-3 pulp-mining larvae) and heavy (>3
larvae, with signs of attack by molds or bacteria).210 BirdsF