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Alejandro Bodrati, Kristina Cockle, José Segovia and Nacho
Areta
 In
general when we talk about migration in birds, we’re thinking
about latitudinal movements – between the North and the South.
But in the Atlantic forest we’ve discovered that several species
migrate longitudinally, from East to West. These birds nest in
spring and summer in the eastern Atlantic forest, in the
mountains of Brazil, and then in autumn they migrate west, to
spend autumn and winter at lower altitudes in Paraguay and
Argentina. This type of migration was not even suspected until
very recently. We’ve proposed it should be called the “Southern
Atlantic Forest longitudinal migratory system”. The species that
make longitudinal migrations of this type include the
Shear-tailed Grey Tyrant (Muscipipra vetula), the
Swallow-tailed Cotinga (Phibalura flavirostris), the
Golden-rumped Euphonia (Euphonia cyanocephala), and the
Black Jacobin (Florisuga fusca).
 These
species, then, are winter visitors that don’t nest in Argentina
or Paraguay. They are all endemic to the Atlantic forest. That
means they live essentially in the humid forest in southeastern
Brazil, the province of Misiones in Argentina, and eastern
Paraguay. The conservation of these birds is complicated because
they migrate through a part of Brazil that has suffered a very
high level of deforestation.
Another characteristic of these species is that their
populations don’t seem to all migrate. While some individuals
stay near the breeding area, others appear to migrate
altitudinally descending to lower altitudes in winter, and still
others migrate hundreds of kilometers to the east and west, also
descending in altitude. We still don’t know where exactly the
birds come from that arrive in Argentina and Paraguay in winter:
we know that they must come from somewhere to the east in
Brazil, but their precise origin is a mystery.
 Shear-tailed
Grey Tyrant (Muscipipra vetula)
The Shear-tailed Grey Tyrant is a rare or uncommon species in
Argentina and Paraguay, but more frequently observed in some
parts of Brazil. It belongs to the Tyrannidae family (Tyrant
flycatchers). Most of its body is grey, but the wings and
the long tail are black.
It feeds on insects, which it often catches by “aerial hawking”.
It sits on an exposed perch, makes a short flight to catch an
insect, then returns to the perch. It generally hunts from the
highest branches of trees or shrubs, often perching on branches
free of leaves where it has a good view of the surroundings.
Occasionally, it will fly to the ground to catch food. Its habit
of perching upright and exposed makes it quite easy to see. It’s
characteristic song is made of two hollow notes, easily
distinguished from the song of other birds in the region. [Listen
to song]
In Argentina, it is considered “threatened” because it has a
very small distribution. It can be seen in small gaps within
primary and secondary forest, as well as in capueras (young
secondary vegetation) and forest edges, mostly between May and
August.
Golden-rumped Euphonia (Euphonia cyanocephala)
 The
Golden-rumped Euphonia is a small and pretty tanager. This
beautiful bird is currently much more common in Argentina than
the other species that have the same type of migratory pattern.
Golden-rumped Euphonias arrive in Misiones in April or May and
stay until September or October when they go back East to their
breeding-ground. When they arrive in autumn in Misiones, and
when they start their trip back to Brazil in spring, they can be
seen in flocks made up of only Golden-rumped Euphonias, in
rather large numbers (8-10 and up to 20 individuals). The rest
of the winter, they can be seen in groups of 3-6 within larger
flocks that include several other species. We often see Golden-rumped
Euphonias in flocks with Blue-naped Chlorophonias (Euphonia
[previously Chlorophonia] cyanea). The best way to find
the Golden-rumped Euphonia is to listen for its complicated
galloping song, which it fortunately sings even in winter. [Listen
to song]
The Golden-rumped Euphonia eats small fruits, especially orange-coloured
fruits of mistletoe (Phorodendron spp.). In the hight
parts of the mountains of Brazil, perhaps fewer mistletoe fruits
are available in winter. In some parts of the breeding grounds,
it even snows in the winter! That might be why the Golden-rumped
Euphonia descends to the west, to places where the winter is
milder and there are mistletoe fruits to eat at the coldest time
of year.
Swallow-tailed Cotinga (Phibalura flavirostris)
The Swallow-tailed Cotinga is a very rare and threatened species
today in Argentina. It belongs to the Cotingidae family. Its
name in Misiones – Tesourinha – comes from the Portuguese word
for “scissors”, because of its long forked tail. It eats small
fruits and insects.
In Argentina the Swallow-tailed Cotinga appears from time to
time, usually between March and September, especially in the
hills in the middle of Misiones, and even in the towns of Tobuna
and San Pedro. Like the Shear-tailed Grey Tyrant, it is quite
passive, medium sized, and perches on exposed branches, so it is
relatively easy to see – when it is present. However, because of
its rarity, it is difficult to find.
Naturalist W. H. Partridge collected a series of 12 individuals
in just one month, between February and March 1952, and he
described the Swallow-tailed Cotinga as “abundant” at that time.
But he never collected the species again (despite almost 10 more
years working in Misiones). From that time until now, there have
been no more documented records (photographs, specimens or sound
recordings) of the Swallow-tailed Cotinga in Misiones, although
there have been sight records. We think Partridge’s observations
in 1952 coincided with the arrival of migratory flocks at his
study area. It’s also possible that more Swallow-tailed Cotingas
were arriving in Misiones at that time than arrive today. We
have observed groups of up to nine individuals near the end of
summer, when the species arrives from Brazil. This beautiful
bird is very quiet, so it is very difficult to detect by ear.
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