6.6. Community Ecology
Major works on the community ecology of birds in
Monteverde include studies on hummingbird popula-
tion dynamics in relation to flower abundance (Fein-
singer 1976,1977,1978,1980), hummingbird pollina-
tion guilds and hummingbird-mediated effects of floral
neighborhoods on pollination success in plants (Fein-
singer et al. 1986,1987,1991a, Feinsinger and Tiebout
1991), relationships between large frugivores and fruit-
ing in the Lauraceae (Wheelwright 1983, 1985, 1988,
1991), seed dispersal by small frugivores (Murray 1987,
1988, Murray et al. 1994), and coevolution among
euphonias, chlorophonias, and mistletoes (Sargent
1994, 1995). Here we summarize these studies; they
are covered in more depth in Chapter 8, Plant-Animal
Interactions.
6.6.1. Guilds
The guild (group of species using the same resource)
is a useful approach to consider subsets of bird com-
munities (Root 1967). Guilds of hummingbirds were
studied in Monteverde for 15 years (Feinsinger 1976,
1980, Feinsinger and Colwell 1978, Feinsinger et al.
1988), particularly in successional habitats along the
cliff edge in Zone 2 (Feinsinger 1976). The Steely-
vented Hummingbird appears to organize the guild
through its aggressive territorial defense of dense
clumps of flowers. The Canivet's Emerald traplines
dispersed flowers that are not defended by Steely-
vented Hummingbirds (see Tiebout, "Do Subordinate
Species Have an Advantage?," pp. 216-218). The Ma-
genta-throated Woodstar visits the same flowers de-
fended by Steely-vented Hummingbirds, escaping de-
tection by its bumblebeelike flight and by foraging in
the highest portions of Inga trees. Whenever detected,
the woodstars are easily displaced by the dominant
Steely-vented Hummingbird. Another core species, the
migratory Green Violetear, which occurs in Monteverde
from October to June, uses a mixed strategy of visiting
rich clumps of flowers (when attacks from Steely-vented
Hummingbirds are infrequent) and traplining dispersed
flowers (when Canivet's Emerald populations are low).
Nine other hummingbird species (plus Tennessee
Warblers) forage for nectar in these habitats (Fein-
singer 1976). These peripheral species arrive for brief
periods to take advantage of surplus flowers. The re-
sources available in the cliff-edge habitats in Monte-
verde are not large enough to support year-round popu-
lations of all species of nectarivorous birds. Nectar
resources located elsewhere that are available when
resources are low in Monteverde maintain the popu-
lations of the majority of species that feed on cliff-edge
flowers (Feinsinger 1980). Combining observations
from Monteverde with other studies in neotropical
mainland and island forests, six roles for humming-
birds in nectar-foraging guilds have been proposed:
high reward trapliners (e.g., hermits of Zones 3-6 in
Monteverde), territorialists (e.g., Steely-vented Hum-
mingbird), low-reward trapliners (e.g., Canivet's Em-
erald), territory parasite-marauder (no Monteverde
example), territory parasite-small filcher (e.g., Magenta-
throated Woodstar), and generalists (e.g., Green Vio-
letear; Feinsinger and Colwell 1978).
A series of ingenious experiments examined the
physiological ecology of captive Steely-vented Hum-
mingbirds and Canivet's Emeralds (Tiebout 1991a,b,
1992, 1993). Energy consumption was measured
with the double-labeled water technique (Tiebout
and Nagy 1991). Each species showed metabolic ad-
justments that allowed it to acclimatize to energetic
stresses when placed individually in flight cages with
high and low quantities of food at either small or large
distances (Tiebout 1991a). The territorialist (Steely-
vented Hummingbird), however, was more stressed
by flying to a distant food source than was the trap-
liner (Canivet's Emerald). When one individual of
each species was caged with a heterospecific, and
nectar "patches" were clumped, territorialist Steely-
vented Hummingbirds maintained better energy bal-
ances than did the competing trapliners (Tiebout 1992).
The trapliners performed better when nectar patches
were dispersed than when they were clumped be-
cause they could better avoid the aggressive terri-
torialists. In the course of day-long experiments with
clumped or dispersed treatments, the two species
adjusted their behavior by concentrating on different
subsets of feeders. This reduced the rate of aggressive
interactions, an adjustment that probably also occurs
in the field (Tiebout 1991a, 1992). Emeralds main-
tained more favorable energy balances when paired
with conspecifics than when paired with a hetero-
specific. In contrast, the aggressive Steely-vented
Hummingbirds suffered higher energetic stress when
paired with conspecifics than when paired with
Emeralds (Tiebout 1993). The "pointer hypothesis"
(Tiebout 1996; see Tiebout, "Do Subordinate Species
Have an Advantage?," pp. 216-218) suggests that the
more aggressive Steely-vented Hummingbirds may
benefit from the food-finding ability of the Emeralds.
The forested habitats in Zones 3-6 support two
distinct guilds of hummingbirds. One guild has short
bills (<25 mm) and exploits flowers with correspond-
ingly short corollas. The second guild has longer,
often curved bills (>28 mm) and visits flowers with
corollas over 30 mm long (Feinsinger et al. 1986).
These guilds are also dominated by few species (the
short-billed Purple-throated Mountain-gem and the
long-billed Green Hermit), with nine other species199 Birds