Table 6.5. Postfledging periods (time during which
fledgling birds remain on their natal territories) of
some birds of Monteverde.
Speciesa
Spotted Barbtail (1)
Rufous-and- white
Wren (2)
Plain Wren (2)
House Wren (2)
Gray-breasted Wood-
Wren (2)
Slate-throated Redstart (3)
Postfledging
Period (days)
60
30-6030-180
21-90
150-18028Habitat
Forest
ForestEdge
Pasture/edge
ForestForestaSources: (1) Powell 1983, (2) Winnett-Murray 1986, (3) Shopland
1985.
The adaptive significance of long post-fledging
periods is poorly understood. Fledglings may remain
with their parents to receive more care and better
learn how to forage than they would on their own
(Young 1996). Parents may also be better at detecting
predators and, by alerting them with alarm notes, give
their fledglings time to take cover (Karr et al. 1990b).
Alternatively, juvenile birds may not disperse because
they have nowhere to go; the habitat may be saturated
with conspecifics, so the best that juveniles can do is
to stay with their parents where they are tolerated but
receive no active parental care.
6.4. Responses to Seasonality
Seasonality in abiotic factors drives phenological
changes in plants, such as flowering, fruiting, and the
production of new leaves (see Chaps. 2 and 3). These
seasonal changes in the flora affect the quantities of
plant resources available to animals and the capacity
of herbivorous insects to exploit their hosts. Although
the degree of the seasonal changes in abiotic factors
varies among life zones, characteristic patterns of
fruit, nectar, and insect abundance occur in each (see
Chaps. 3 and 4). Birds respond to some of these sea-
sonal changes by adjusting their reproduction and
molt schedules; some species migrate to track the
changing abundance of resources (Feinsinger 1977,
Wheelwright 1983, Young 1994a, Powell and Bjork
1995).
6.4.1. Migration
Hummingbirds show seasonal movements that are
most obviously tied to seasonal resource abundance.
Several species occur in Monteverde only when cer-
tain plants are flowering. For example, visits of the
Magenta-throated Woodstar and the Blue-throated
Goldentail (September-April) coincide with flower-
ing peaks of Lobelia laxiflora and Inga brenesii (Fein-
singer 1977). Similarly, the Plain-capped Starthroat
migrates to Monteverde from the Pacific lowlands
when the vine Mandevilla veraguasensis blooms
(May-August; Feinsinger 1977, 1980). On the Carib-
bean slope, three hummingbird species (White-necked
Jacobin, Brown Violetear, and Green Thorntail) are
most abundant when Inga oerstediana blooms (March-
June; Fogden 1993). These flowers also attract Steely-
vented Hummingbirds that fly over the divide from
Zones 1 and 2 on the Pacific slope where they occur
for the remainder of the year (Fogden 1993). Other
hummingbird species occur in Monteverde season-
ally, but the reasons are more complex than the at-
traction of one or two species of plants (Feinsinger
1977).
Other species undergo elevational migrations to or
from Monteverde. Quetzal movements appear to track
geographical differences in the abundance of laura-
ceous fruits (Wheelwright 1983). At the community
level, elevational migration has been studied more
intensively on the Caribbean slope of the Cordillera
Central where the seasonal occurrence of frugivores
in mist nets is positively correlated with fruit abun-
dance (Loiselle and Blake 1991). Seasonal occurrence
of migrant nectarivores in other lowland and mid-
elevation forest is also correlated with flower avail-
ability (Stiles 1978, 1980a, 1985c). Breeding by low-
land frugivores, however, is negatively correlated
with local fruit abundance. The presence of seasonal
migrants may complicate that situation, however, be-
cause many residents breed after the migrants have
left (Rosselli 1989, Loiselle and Blake 1991). Popula-
tions of lowland insectivores generally do not make
local seasonal movements (Levey and Stiles 1992).
Because the Caribbean slope of the Cordillera de
Tilaran in Monteverde shares similar climate, life
zones, and fauna with the Caribbean slope of the Cor-
dillera Central, the patterns of migration of Monte-
verde's frugivores and nectarivores are probably simi-
lar; more studies are needed to confirm this pattern.6.4.2. Physiological Ecology
Fierce winds whip cool horizontal precipitation in the
higher elevation areas of Monteverde from December
through early March, and presumably birds have
physiological adaptations to these conditions. Many
species (e.g., House Wrens, Brown Jays) do not begin
breeding until these early dry-season winds subside
(Lawton and Lawton 1985, Young 1994a). If the wind
and mist resume after the onset of nest building, both
species stop all nesting activities until the weather194 Birds