lowland butterfly species migrate. The general pattern
is emigration from the Pacific side during October to
February; they return with the rains in April or May.
The exact timing varies among butterflies. For ex-
ample, some clearwing butterflies (Nymphalidae-
Ithomiinae) fly through in October, pierids in Decem-
ber, and lycaenids even later. A subset of species
migrate from the Pacific to the Atlantic side during
the short dry period called "veranillo" from late June
through early July. This migration consists of the first-
generation offspring of Atlantic slope migrants that
arrived during April and May. An alternative to mi-
gration for a minority of species of the Pacific slope
is to pass the dry season in reproductive diapause, a
physiological condition in which courtship and egg
maturation are inhibited hormonally.
Although migration is not a visually dramatic phe-
nomenon, migrating butterflies are easy to observe
in Monteverde. A good place to see migration is at
"Windy Corner," located at the entrance to the MCFP,
just as the road curves sharply to the left, about 0.5
km before the MCFP headquarters. The road runs east-
west, the general direction of the migration. Some of
the best days are early in the dry season (November
and December), between 1000 and 1300 hr. On the
first warm sunny day after a spell of cloudy and rainy
weather, hundreds of butterflies fly against the trade
winds, headed eastward toward the Continental Di-
vide and the Atlantic slope.
If the wind is brisk, the butterflies fly low, within
2 m of the road surface. Some species, such as Anartia
fatima (Nymphalinae), fly within 30 cm of the ground.
If the wind averages 6 m/s (about 15 miles/h), only
the strongest fliers, mainly the skippers (Hesperiidae),
can make it through the gap. The majority of nympha-
lids remain wind-blocked 150 m up the road at the
head of the road cut. In brief periods when the wind
dies down, some of the stronger nymphalids can ease
through. Great swirls of wind produce complex flight
tracks; the butterflies sometimes stop in mid-air or
suddenly shoot upward, or they get caught in a gust
and sail backward. When the wind speed decreases,
the butterflies migrate higher above the ground, reach-
ing heights of over 100 m.
In our counts of butterflies migrating through the
road cut at Windy Corner during 1994-96, the record
observation (16 December 1994) was 6000 butterflies
in 5 hours, with a peak intensity of more than 80 in-
dividuals/min. The vast majority were skippers. An
experienced field worker can identify many of the
butterfly species as they fly past, but it is often nec-
essary to see skippers and lycaenids up close to iden-
tify them. One can catch 40 species in a few hours.
On calmer days, one can also observe dragonflies,
flies, beetles, bugs, parasitic wasps, and day-flying
moths migrating along with butterflies (see William-
son and Darling, "La Ventana," p. 438).
The amazing diversity of migrant species in Costa
Rica and how they depend on different habitats over
a range of elevations have only recently been recog-
nized (Haber 1993, W. Haber and R. Stevenson, un-
publ. data). Some migratory species are more vulner-
able to population decline than nonmigratory species
because migrants depend on at least two different
habitats and on the resources along their migratory
routes. Thus, preserving habitat at one location is
not sufficient to ensure the survival of a migrating
species.4.5.3. Manataria maculata
(Islymphalidae: Satyrinae)
Rob Stevenson & William A. Haber
Manataria maculata is the largest species of wood
nymph in Monteverde. Its dark brown wings with six
or seven white spots on both the upper and lower
sides of the forewing apex distinguish it from other
local butterflies. The scalloped hindwing bears a cryp-
tic pattern of eyespots on the underside. Many people
are startled by their first encounter with Manataria]
dozens of butterflies suddenly explode outward in all
directions from a shaded embankment, treehole, or
dark hiding place along a forest trail. Clustering to-
gether during the day in aggregations ranging from
a few individuals to more than four dozen, these
satyrines fly into the canopy at dusk, where they
spend the night roosting alone. At dawn, they return
to their diurnal groups.
Manataria's behaviors mark it as an unusual but-
terfly. Like a hawkmoth, it vibrates its wings before
flying to warm its flight muscles to 7-10°C above the
ambient temperature. It flies almost exclusively at
dawn and dusk. It is one of few butterfly species in
which the same individuals migrate up and down the
mountains. It has a potential life span of a year or more
but breeds for only one month and does not mate until
it is 8-10 months old. As with other satyrines, it feeds
on rotting fruit and tree sap instead of nectar, but it
seeks food during the day, rather than during its usual
crepuscular activity period.
These butterflies are found in Monteverde from the
end of June until the following April or May. In Monte-
verde, all individuals are in reproductive diapause,
waiting to return to the Pacific lowlands where they
mate and breed on species of bamboo at the beginning
of the wet season. The eggs are laid in clusters and
the larvae continue to feed in groups until the last
instar. Almost immediately on emerging from the
plain green chrysalis between the end of June and
August, most adults fly eastward, upslope to Monte-119 Insects and Spiders