aggression against their bearers. By the time males
attain definitive plumage, they probably recognize
one another individually by vocalizations and behav-
ior, and the "newcomers' badge" may no longer pro-
vide an advantage (McDonald 1993a).6.2.4. Vocalizations
Vocalizations have been analyzed for three bird spe-
cies in Monteverde, all of which have lek breeding
systems. Long-tailed Manakins have a repertoire of
at least 13 functionally and audially distinct vocal-
izations that serve in signaling between partnered
males, in male-male aggression, and in dual-male
courtship songs aimed at females. This large reper-
toire of functionally distinct vocalizations appears
to have evolved as an aspect of the long-term coop-
erative relationships among males (Trainer and
McDonald 1993; see Trainer, "Roles of Long-Tailed
Manakin Vocalizations," p. 215).
Three-wattled Bellbirds are best known for their
loud, ringing "Bong!" song, but males vary consider-
ably in their associated screeching and hissing vocali-
zations. During the breeding season, males shout their
"Bong!" throughout the day from exposed perches in
the canopies of tall trees (Fig. 6.2). When a female
joins a male on its perch, the male faces the female's
ear and continues singing at full volume. Copulation
may follow a series of calls if the female does not fly
away (Snow 1977).
Male Green Hermits also give monosyllabic songs
from their perches 0.75—1.75 m high in the cloud for-
est. Song rate varies between 34/min when males are
alone to 57/min when other males are present. Green
Hermits have three or four other calls that they give
during male-male chases, male flight displays, and
foraging (Snow 1972, M. Harger, unpubl. data).
6.3. Reproductive Biology6.3.1. Phenology
All of the life zones in Monteverde are seasonal, with
a distinct January to mid-May dry season (see Chap. 2,
Physical Environment). Nesting in most bird species
is also seasonal, with the majority of species nesting
between March and July. Most species studied fit this
pattern: Emerald Toucanet (Riley 1986), Yellow-
throated Euphonia (Sargent 1993), Brown Jay (Lawton
and Lawton 1985), Spotted Barbtail (Powell 1983),
Resplendent Quetzal (Wheelwright 1983), Long-tailed
Manakin (McDonald 1989b), Gray-breasted Wood-
Wren (Winnett-Murray 1986), Rufous-and-white
Wren (Winnett-Murray 1986), Plain Wren (Winnett-Murray 1986), and House Wren (Winnett-Murray
1986, Young 1994a). Captures of birds with brood
patches and fledgling birds in mist-net studies (D.
McDonald, B. Young, G. Powell, unpubl. data) sup-
port this trend. The major exceptions to this pattern
are the hummingbirds. Most nesting records of hum-
mingbirds (e.g., Steely-vented Hummingbird, Rufous-
tailed Hummingbird, Coppery-headed Emerald) are
from October through January (Feinsinger 1977). The
Green Hermit and Purple-throated Mountain-gem, in
contrast, may breed through much of the year (Fein-
singer 1977, F. G. Stiles, unpubl. data).
Why do Monteverde's birds breed when they do?
Frugivores may nest when fruits are especially abun-
dant. For example, quetzals nest when many trees in
the family Lauraceae produce fruits. Lauraceous fruits
comprise a large portion of the diet of adults, so quetzals
may time their breeding to take advantage of their food
resource base (Wheelwright 1983). Similarly, the
October-January breeding season for hummingbirds
coincides with the period when many hummingbird-
pollinated plants (e.g., Hansteinia, Razisea, Drymonia,
Cavendishia, Kohleria, Cuphea, Malvaviscus, and Inga)
have their annual flowering peak (Feinsinger 1978,
Feinsinger et al. 1986; see Chap. 3, Plants and Vegeta-
tion). Insectivores, on the other hand, may not depend
on a superabundant resource base to produce eggs or
feed young. The breeding season of insectivores spans
the latter half of the dry season and the early wet sea-
son. In the late dry season, arthropod biomass is typi-
cally at its annual low (Feinsinger 1976, Buskirk and
Buskirk 1976, Young 1994a), indicating that food is not
a crucial resource for nesting insectivores during this
period. Instead, birds may time their breeding so that
their offspring disperse during the period of increas-
ing food abundance that occurs throughout the first
two-thirds of the wet season (Buskirk and Buskirk 1976,
Young 1994a).6.3.2. Nesting
Monteverde has been the site of studies on the nest-
ing biology of 15 bird species. Original nest descrip-
tions of five species are from Monteverde: Three-
wattled Bellbird (Snow 1977), Black-and-yellow Silky
Flycatcher (Kiff 1979), White-eared Ground-Sparrow
(Winnett-Murray 1985), Azure-hooded Jay (Winnett-
Murray et al. 1988), and Black-breasted Wood-Quail
(McDonald and Winnett-Murray 1989). The first Costa
Rican nests of the Sunbittern were described from
Monteverde (Lyon and Fogden 1989). Preserved egg
sets of Monteverde birds are at the Universidad de
Costa Rica, the Burke Museum of the University of
Washington, and the Western Foundation for Verte-
brate Zoology.190 Birds