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Descrevemos uma nova espécie de tamnofilídeo (Thamnophilus divisorius, Chocado-Acre) oriunda de serra do Divisor, Acre, Brasil. A nova espécie é conhecida de apenas um único cume de serra (embora é esperada existir em outras áreas similares ainda não pesquisadas nos arredores), e é comúm no interior de bosques de vegetação baixa crescendo em solos pobres que lembram habitats de campina de areia branca e vegetações afins nos Guianas e na Amazônia. é filogeneticamente mais próximo de Thamnophilus insignis (Choca-de-Roraima), espécie de distribuição restrita à região de pantepui, e forma um clade com Thamnophilus amazonicus (Choca-canela). Thamnophilus divisorius ocorre numa região remota dentro de um parque nacional e, apesar de ter uma distribuição extremamente restrita, estamos otimistas sobre a sua sobrevivência no futuro.
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I J 1996, the fi eld phase of a manage-
ment plan for the Parque Nacional da Serra
do Divisor (PNSD) in Acre, Brazil, was initi-
ated. The project was funded by The Nature
Conservancy International of Alexandria,
Virginia, and coordinated in Brazil by the
national offi ce of The Nature Conservancy in
Brasília, D.F., the nongovernmental organiza-
tion S.O.S. Amazônia in Rio Branco, Acre, and
the national and regional offi ces of the Instituto
Brasileiro do Meio Ambiente e dos Recursos
Naturais Renováveis (IBAMA). One key aspect
of the project was a rapid ecological evaluation
(REA; Sobrevila and Bath 1992) of the park’s
ora and fauna. The ornithology section of
the Museu Paraense Emílio Goeldi (MPEG) in
Belém, Pará, was responsible for the avifaunal
inventory; B.M.W., D.C.O., and the technician
D. C. Pimentel Neto conducted the fi eld work.
Although the fi rst phase encompassed only 18
eld days, with observations divided among
six sites in the northern sector of the park, we
documented several species of birds previously
unknown or poorly known in Brazil, including
a striking Thamnophilus antshrike new to sci-
ence, which we propose to name:
Thamnophilus divisorius sp. nov.
Acre Antshrike
Choca-do-Acre (Portuguese)
Holotype.—MPEG no. 52754; adult male,
from Morro Queimado, in the Serra da
Jaquirana (one of the easternmost ridges in
the Serra do Divisor), above the le bank of
the rio Moa in Parque Nacional da Serra do
Divisor, Municipality of Mâncio Lima, Acre,
Brazil (07°26’36”S, 73°40’28”W); 500 m; col-
lected 10 July 1996 by B.M.W., prepared by D.
C. Pimentel Neto. Tape-recorded by B.M.W.,
Macaulay Library of Natural Sounds (MLNS),
A.—We describe a new species of Thamnophilus antshrike—T. divisorius (Acre
Antshrike)—from the Serra do Divisor of Acre, Brazil. The new species is known from a single
small ridge (though we expect that it is present on other, unexplored ridges in the Acre Arch
uplands), and is common in the interior of shrubby woodlands on poor soil physiognomically
similar to white-sand habitats in the Guianas and Amazonia. Thamnophilus divisorius is sister
to T. insignis (Streak-backed Antshrike), a narrow endemic of pantepui, and forms a well-
supported clade with that species and T. amazonicus (Amazonian Antshrike). Thamnophilus
divisorius occurs in a remote region within a national park in Brazil; despite its limited range, we
are optimistic about its future survival. Received 16 May 2003, accepted 24 June 2004.
R.— Descrevemos uma nova espécie de tamnofi lídeo (Thamnophilus divisorius, Choca-
do-Acre) oriunda da serra do Divisor, Acre, Brasil. A nova espécie é conhecida de apenas um
único cume de serra (embora é esperada existir em outras áreas similares ainda não pesquisa-
das nos arredores), e é comúm no interior de bosques de vegetação baixa crescendo em solos
pobres que lembram habitats de campina de areia branca e vegetações afi ns nos Guianas e na
Amazônia. É fi logeneticamente mais próximo de Thamnophilus insignis (Choca-de-Roraima),
espécie de distribuição restrita à região de pantepui, e forma um clade com Thamnophilus
amazonicus (Choca-canela). Thamnophilus divisorius ocorre numa região remota dentro de um
parque nacional e, apesar de ter uma distribuição extremamente restrita, estamos otimistas
sobre a sua sobrevivência no futuro.
1Museum of Natural Science, 119 Foster Hall, Louisiana State University, Baton Rouge, Louisiana 70803, USA;
2Departamento de Zoologia, Museu Paraense Emílio Goeldi, Caixa Postal 399, 66.017-970, Belém, Pará, Brazil
B M. W,1,3 D C. O,2,4  R T. B1
A NEW SPECIES OF THAMNOPHILUS ANTSHRIKE
(AVES: THAMNOPHILIDAE) FROM THE SERRA DO
DIVISOR, ACRE, BRAZIL
The Auk 121(4):1031–1039, 2004
3E-mail: ictinia@earthlink.net
4Present address: Conservation Priorities Coor-
dinator, The Nature Conservancy, Eastern South
America Division, SHIN Centro de Atividades 05
Conjunto J Bloco B, 3o Andar, 71.503-505 Brasília, D.F.,
Brazil.
1031
W, O,  B
1032 [Auk, Vol. 121
Cornell Laboratory of Ornithology, Ithaca,
New York, no. 79060; Arquivo Sonoro Elias P.
Coelho (ASEC), Universidade Federal do Rio de
Janeiro, Rio de Janeiro, Brazil, no. BMW 054/10;
and Isler inventory, Alexandria, Virginia, no.
BMW.125:21.
Diagnosis: Morphology.—Allocation of the new
species to the genus Thamnophilus is diffi cult to
justify objectively on the basis of morphology,
because characters of diagnostic value have not
been identifi ed for the genus and because the
present group of 25 species (as currently classi-
ed) may not be monophyletic. The type species
of Thamnophilus is T. doliatus (Barred Antshrike),
which is barred black-and-white in the male
plumage, and mostly rufous-brown in the
female plumage. These factors notwithstanding,
the new species is most similar morphologically
to members of Thamnophilus. Adult males are
readily distinguished from other Thamnophilus
species by a combination of the following
characters: entirely dark-bluish-gray plumage
with somewhat blacker hood, wings, and tail,
and mo led grayish (rather than mostly white)
underwing coverts. Adult females diff er distinc-
tively from other Thamnophilus species in hav-
ing almost uniformly bluish-gray facial region
and upperparts with slightly darker wings and
tail, and entirely brownish-orange underparts.
Both sexes may show minute pale spots (white
in male, buff -orange in female) at tips of some
upperwing coverts; both sexes have small but
more conspicuous spots at the tips of the outer
two rectrices; those are reduced to fringes or are
absent on the next one or two rectrices.
Diagnosis: Voice.—The loudsong (following
Willis 1967) of T. divisorius is similar in pa ern,
structure, and auditory quality to that of T.
doliatus (especially the nominate form), which
aligns T. divisorius more objectively with the
genus Thamnophilus than does its morphology.
That alignment is supported anecdotally: on the
morning of its discovery, T. divisorius was heard
and tape-recorded by B.M.W. for nearly an hour
before being seen, and it was clear from its song
that it was an unnamed Thamnophilus antshrike.
Thamnophilus divisorius‘ loudsong diff ers from
the song of all other Thamnophilus species by the
following combination of characteristics: (1) it
accelerates in pace (progressively shorter inter-
note intervals) for approximately half its dura-
tion, slowing slightly and gradually through the
nal two or three notes; (2) its terminal note, and
o en the penultimate note, is louder, longer, and
of slightly higher peak frequency than the rest
of the series, but does not diff er dramatically in
structure or tonality. Recorded calls appear to be
less clearly diff erentiated from those of several
other Thamnophilus species.
Distribution.—Known only from the type
locality, the new species probably occurs on
other, physiognomically similar ridges in the
Acre (sometimes called Serra do Moa) Arch
uplands in the Serra do Divisor of Acre, perhaps
extending to the continuous Sierra Contamana
in Ucayali, Peru (Fig. 1).
Description of holotype.—(See cover plate.)
Alphanumeric color designations were deter-
mined from direct comparison with the Munsell
(1994) soil color chart. Crown from base of bill
to nape semi-glossy black with a few sca ered
albino feathers in forehead and occipital–nuchal
regions; not crested. Sides of head and neck
a fl a er black, less intense and lacking gloss.
Feathers of back and scapulars same black as
sides of head, widely margined with subtly paler
bluish black (nearest Gley 2, 2.5/1/5PB), impart-
ing a weakly mo led eff ect, which is seen to
vary with viewing angle. Rump and uppertail
coverts dark bluish gray (Gley 2, 3/1/5PB). No
white interscapular patch; those feathers instead
dull grayish. Throat subtly grayer than sides of
head but darker than remainder of underparts,
which—together with black head and neck
region—contributes to a weakly hooded eff ect.
Underparts from breast to undertail coverts,
including elongated, loosely integrated fl ank
feathers, uniform dark bluish gray, concolor
with rump. Upperwing coverts and tertials
same semiglossy black as crown. Tiny feathers at
base of outer primary whitish; feathers at bend
of wing mixed gray and whitish. Underwing
coverts with gray centers and whitish tips,
or a single, whitish, internal band encircling
gray center, producing a mo led appearance.
Primaries blackish, subtly paler on outer edges
(visible on folded wing), all except outermost
with contrasting wide silvery-white margins
1–2 mm on inner webs, especially visible on ven-
tral surface, those margins becoming progres-
sively more extensive from outermost primary
(which is shorter and wholly blackish) to inner-
most. Tail graduated, same semiglossy black as
crown and upperwing coverts. Outermost rectrix
with white tip 1.5 mm wide, extending to both
webs; tips present but decreasing in size on next
New Antshrike from Acre, BrazilOctober 2004] 1033
three pairs of rectrices; two central pairs with
worn tips but apparently lacking any white. So
parts in life: iris clear chestnut brown; maxilla
black; mandible black; legs and feet dull bluish
gray; soles yellow.
Measurements of holotype.—Bill width at ante-
rior edge of nares 4.9 mm; bill depth at anterior
edge of nares 5.7 mm; culmen from anterior edge
of nares 13.0 mm; culmen from base (at skull)
20.8 mm; wing chords 75.6 (le ) and 76.2 (right)
mm; tail 65.2 mm; tarsus 21.6 mm; mass 23.0 g.
Skull 100% ossifi ed; le testis 7.9 × 4.8 mm.
Description of allotype.—(See cover plate.)
MPEG no. 52751. Crown feathers from base of
bill to occipital region blackish with dark blu-
ish gray (Gley 2, 3/1/5PB) margins, imparting a
weakly mo led eff ect. Sides of head and malar
region same dark bluish gray (auricular feath-
ers with orangish sha s), tinged with brown-
ish on sides of neck. Remainder of upperparts
uniform dark bluish gray, with individual
feathers darkest toward center. Feathers of
chin and throat deep ochraceous with cream-
white center and gray base, such that throat
F. 1. Composite LANDSAT image of the northern half of Parque Nacional da Serra do Divisor (white out-
line), Acre, Brazil. The single confirmed locality of Thamnophilus divisorius, “Morro Quiemado,” is indicated by
an × ; it is slightly north of the Rio Moa in the Serra da Jaquirana. The view from the ridge, looking northwest,
is shown in Figure 2. The ridge system comprising the Acre Arch uplands appears as a textured band running
northwest into Ucayali, Peru; a somewhat disjunct system south of the Moa appears to be lower in relief. These
areas are virtually unexplored biologically. We expect that T. divisorius will eventually be found on most, per-
haps all, of the higher ridges in the region.
W, O,  B
1034 [Auk, Vol. 121
appears mo led; face versus throat contrast is
strong. Remainder of underparts deep ochra-
ceous or brownish orange (7.5YR 5/8), washed
subtly darker at sides of breast (7.5YR 4/6) and
brightest in midbelly. Underlying fl ank feathers
extensively bluish gray with brownish-orange
tips. Upperwings same blackish as crown;
most lesser, median, and greater wing coverts
weakly tinged brownish orange on outer webs
near tips, not suffi ciently strongly to form wing-
bars or a clear pa ern of margination. Primary
coverts blackish. Outer webs of inner primaries,
secondaries, and tertials also faintly tinged
brownish orange. Tiny feathers at bend of wing,
and underwing coverts, same brownish-orange
as breast and belly. Primaries blackish, marked
with same pa ern of pale margination on outer
webs as in holotype, but color somewhat more
buff (near 7.5YR 8/4). Tail as in holotype but pale
tips limited to outer rectrix, reduced in size, and
buff -orange instead of white. So parts in life:
iris clear chestnut brown; maxilla dark gray;
mandible dark gray with pale-horn base (vis-
ible only from below); legs and feet dull bluish
gray, soles yellow.
Measurements of allotype.—Bill width at anterior
edge nares 4.7 mm; bill depth at anterior edge
nares 5.6 mm; culmen from anterior edge nares
11.5 mm; culmen from base (at skull) 20.6 mm;
wing chords 71.6 (le ) and 70.9 (right) mm; tail
63.8 mm; tarsus 21.0 mm; mass 22.7 g. Skull 100%
ossifi ed; ovarian mass 4.2 × 2.1 mm; size of largest
ovum not recorded, oviduct smooth.
Specimens examined: Skins.Thamnophilus divi-
sorius: Brazil, Acre (four males, three females, one
sex unknown; MPEG nos. 52748–52755). In addi-
tion, plumages of specimens of all other species
of Thamnophilus were compared visually at the
MPEG, Louisiana State University Museum of
Natural Science (LSUMZ), and the Academy of
Natural Sciences of Philadelphia (ANSP), though
it was not possible to compare specimens at the
la er directly with those of the new species.
Specimens examined: Tape recordings.
Thamnophilus divisorius: Brazil, Acre (7, repre-
senting at least 13 individuals and 4 vocalization
types). All specimens were tape-recorded prior
to collection. Recordings of all other species and
most subspecies of Thamnophilus were com-
pared superfi cially. Recordings of T. divisorius
have been or will be deposited at MLNS, ASEC,
MPEG, and the antbird research inventory of
Phyllis and Morton Isler.
Biochemical specimens.—MPEG voucher speci-
men numbers, followed by biochemical sample
numbers, are 52749 (PNSD 223), 52750 (PNSD
224), 52751 (PNSD 225; allotype), 52752 (PNSD
226), 52753 (PNSD 227), and 52754 (PNSD 228;
holotype). Samples of liver and heart tissue
are preserved in plastic tubes containing 20%
DMSO and EDTA buff er solution, and are cur-
rently stored at MPEG. Among many tissue
samples analyzed in construction of a phy-
logeny of the genus Thamnophilus, especially
pertinent to this description were those of T.
amazonicus (Amazonian Antshrike; LSUMZ
No. B13045) and T. insignis (Streak-backed
Antshrike; LSUMZ No. 7486).
Etymology.—The name divisorius is an latinized
adjectival form of the Portuguese word divisor
(i.e. boundary) and is given in recognition of the
great importance of the Parque Nacional da Serra
do Divisor, where the new antshrike was discov-
ered. The English name, Acre Antshrike, and the
Portuguese Choca-do-Acre, call a ention to the
Brazilian state of Acre where the park is located
and where the state government plays a critical
role in environmental protection of a large area
of western Amazonian Brazil.
R
Variation in the type series.—The type series
comprises the eight specimens listed above.
Three adult males vary slightly from the holo-
type in having minute white spots or tiny
whitish fringes on the outer webs at the tips of
some (especially innermost) greater upperwing
coverts. These whitish markings are discernible
only on close examination. Specimen MPEG no.
52755 also has a tiny whitish fringe on the outer
web of two scapular feathers, and MPEG no.
52752 has a single albino crown feather. The lat-
ter specimen also shows the most clearly defi ned
blackish hood of all. Among females, MPEG
nos. 52749 and 52750 show slightly less black-
ish in the crown than the allotype (described
above). The most notable variation in the series
of four female-plumaged specimens (including
MPEG no. 52748, which is sex unknown, and
represented by only the head and part of the
upper breast, and most of one wing) is seen in
the upperwing coverts. Specimen MPEG no.
52748 has pale brownish-orange fringes on the
lesser, median, and greater coverts; no. 52749
has rather distinct orange-buff spots on the
New Antshrike from Acre, BrazilOctober 2004] 1035
outer webs of the median and greater coverts.
The allotype and MPEG no. 52750 are closely
similar, though the la er has slightly more dis-
tinct pale margins on the tertials. All specimens
were judged to have 75–100% ossifi ed skulls
except female no. 52750, which was unossifi ed.
That specimen, a juvenile, also had the smallest
ovary mass (2.3 × 1.1 mm) of the three known
females. That its plumage so closely matches
that of the allotype, which is apparently an
adult female, indicates that the juvenal plumage
of the female (at least) is almost indistinguish-
able from that of the adult female. Males have
a well-developed hook with a slightly basad
notch at the tip of the maxilla, which seems to be
more formidable (for the bird's size) than those
of most other Thamnophilus antshrikes. Female
maxillas appear to be less strongly hooked, but
there are no signifi cant morphometric diff er-
ences between the sexes. Some standard mea-
surements are presented in Table 1.
Habitat.—The region of serras that straddles
the Brazil–Peru frontier (the Serra do Divisor
in Brazil) is known geologically as the Acre
(or Serra do Moa) Arch and is postulated to
be Mio-Pliocene in age (Jordan 1983, Mégard
1984). Thamnophilus divisorius is known from
a single ridge in the more restricted Serra da
Jaquirana, the easternmost of a series of nar-
row, roughly north–south ridges in the Serra do
Divisor, which rises abruptly above a vast, level
plain cloaked in tall forest (Fig. 2A). Soil here
is extraordinarily thin, sandy, and well-drained
owing to highly vertical relief and millenia of
rainwater surface denudation. What li le soil
remains is buried beneath a deep humus of leaf
li er and springy root masses. Consequently,
plant diversity is limited and trees are con-
spicuously shorter in comparison with the
surrounding forest, which is only slightly
downslope. On the ridgeline, trees grow in high
density; however, most are <20 cm diameter at
breast height (dbh) and <15 m tall, with nar-
row canopies. Most taller trees are in the fam-
ily Fabaceae. Understory is dominated by two
species of plants: (1) extensive, homogeneous
stands of an unidentifi ed, smooth-leaved, 0.5–
1 m tall, light-green terrestrial bromeliad; and
(2) sca ered thickets of Gleichenia sp. ferns inter-
twined with thin vines and tree trunks (Fig. 2B).
Plants form impenetrable thickets where the
broken canopy permits sunlight to reach the
understory for much of the day. Several spe-
cies of melastomes were also among the most
common understory plants. A lightning strike
that occurred in 1995 (information from local
residents) burned 0.25 ha of forest at the crest
of the ridge and was hot enough to completely
kill all vegetation. Vegetation on the poor soil
had barely begun to grow back several months
later (July 1996).
This fl oristically simple, low-stature ridge
forest is physiognomically similar to “stunted
woodland” habitats found on the upper slopes
of summits across pantepui and in the white-
sand “Amazon caatinga” habitats described in
Anderson (1981). It is likewise similar to the
varillal woodland described by Whitney and
Alvarez (1998) and Alvarez and Whitney (2003),
who also highlighted the patchy distribution of
those habitats in Amazonia and their contribu-
tion to terra fi rme habitat mosaicism and overall
species diversity of birds. Interestingly, T. diviso-
rius was not found by B.M.W. during three days
in April 1997 in a much more extensive, generally
taller, and biologically more diverse “Amazon
caatinga” woodland 100 km east-southeast of
the type locality (or 50 km west-northwest of
the town of Cruzeiro do Sul). Some areas of that
caatinga woodland were structurally similar to
T 1. Some standard measurements of Thamnophilus divisorius.
Culmena Wing chordb Tai l Tarsus Body mass
(mm) (mm) (mm) (mm) (g)
Male 20.6 72.8 63.2 21.0 22.3c
(range: 20.1–21.5) (range: 70.8–76.2) (range: 61.3–65.2) (range: 20.5–21.6) (range: 21.0–23.0)
(n = 4) (n = 4) (n = 2) (n = 4) (n = 3)
Female 20.0 70.8 63.2 20.8 22.1
(range: 19.6–20.6) (range: 70.3–71.6) (range: 61.6–64.3) (range: 20.6–21.0) (range: 21.0–22.7)
(n = 3) (n = 3) (n = 3) (n = 2) (n = 3)
aFrom base at skull.
bBoth wings measured, with longest measurement included here.
cLightest male (21.0 g) missing tail.
W, O,  B
1036 [Auk, Vol. 121
the ridge forest (though the ground was level
and poorly drained, with none of the unidenti-
ed terrestrial bromeliad present); almost all of
the avian species encountered on the ridge were
also found in the caatinga woodland. Although
only one small area of the woodland was briefl y
surveyed, T. divisorius is such a conspicuous spe-
cies by voice that we suspect that its apparent
absence may be real. Multiple tape-recording
playbacks of loudsongs from the type locality
failed to elicit a response.
Behavior and ecology.Thamnophilus divisorius
is a common bird but is generally secretive and
diffi cult to detect except by its vocalizations.
Pairs foraged apart from mixed-species fl ocks
(few of those were encountered on the ridge),
keeping mostly within 3 m (o en within 1 m)
of the ground within forest. Some individuals
rose to as high as 8 m a er tape-recording
playback. Birds advanced with short hops,
stopping briefl y on both horizontal (usually) or
vertical perches, and frequently “hitched” (fol-
lowing Whitney and Pacheco 1994) upward on
thin trunks and vines before hopping or fl ying
a short distance to a new perch. Most forag-
ing a ack maneuvers were reaches and gleans
to woody and herbaceous substrates within a
few centimeters of the head, but males were
twice seen to perform upward sally-strikes or
sally-pounces of 1 m in range to the under-
sides of leaves (terminology follows Remsen
and Robinson 1990). Those strikes involved
violent contact of the foreparts of the bird
with foliage. Small arthropods were captured
several times, including at least one caterpil-
lar and a green orthopteran 3 cm in length,
which was beaten vigorously against a limb
before being swallowed whole. Thus, foraging
behavior was much like that of many other spe-
cies of Thamnophilus (Whitney et al. pers. obs.).
Thamnophilus divisorius did not display any dis-
tinctive wing or tail motions.
Vocalizations.—The loudsong (n = 6 adult
males, 3 adult females, and 1–2 of unknown
sex and age recorded) of T. divisorius is an
unevenly paced series of approximately 15–25
(usually 20) structurally similar notes that
accelerates gradually, then slows slightly
through the fi nal two or three notes, the whole
song lasting about 2 s (Fig. 3A). As the series
accelerates, it also drops slightly in frequency
(<0.3 kHz), then rises just slightly more than
that through the fi nal fi ve or so notes to fi nish
at 2.0 kHz. The fi rst note is separated from
the second by an interval of 0.1–0.2 s, which
is longer than that between any other pairs of
notes. The terminal note, and o en the penul-
timate, are structured like other notes of the
series, but are both louder and slightly longer,
as well as peaking at the highest frequency of
all. Female loudsongs (specimens collected to
document sex) are slightly lower in frequency
(0.2–0.3 kHz) than those of males, as judged
by the peak frequency of the terminal note.
F. 2. Parque Nacional da Serra do Divisor, Acre,
Brazil. (A) View from the easternmost ridge in the
Serra da Jaquirana at “Morro Queimado,” type local-
ity of Thamnophilus divisorius (marked × in Fig. 1),
looking northwest over the system of ridges forming
the Acre Arch. The ridges are narrowly capped with a
homogeneous shrubby woodland growing on deeply
weathered soil physiognomically very different from
forest only slightly downslope. The long, high ridge
on the horizon, which is probably the one visible in
Fig. 1 at 07°22’S, 73°48’W, would be especially in-
teresting to explore. (B) Microhabitat of T. divisorius
at the type locality. Thin-trunked trees with narrow
canopies partially shade a nearly impenetrable
growth of an unidentified bromeliad and Gleichenia
ferns. Photograph was taken in a relatively open
place. (Photos by B.M.W., July 1996.)
New Antshrike from Acre, BrazilOctober 2004] 1037
Three types of calls were recorded. One is a
short, unmodulated (following Isler et al. 1998),
slightly descending note with weak harmonics
that is sometimes delivered in pairs, the two
notes being separated by 0.25 s (n = 2 record-
ings; Fig. 3B). It was given repeatedly on one
occasion by an adult male a er collection of
either its mate or an off spring (sex and age not
determined for that specimen). The most com-
monly heard call (n = 3 recordings) was a short,
throaty growl believed to be homologous to the
caw call described for the T. punctatus complex
by Isler et al. (1997). The caw of T. divisorius is
an unmodulated, nearly symmetrically hill-
shaped note with pronounced harmonics (Fig.
3C). It is given by both sexes and appears to
function primarily to communicate heightened
awareness, such as when a potential threat
is detected (e.g. a nearby observer). It is not
normally delivered during routine foraging.
The fi nal call type recorded for T. divisorius is
a quiet cha er, which was given by a juvenile
(MPEG no. 52750) as it accompanied an adult
male and female. The sound is almost certainly
a food-solicitation call.
Phylogenetic relationships and origin.—DNA
sequences from the mitochondrial cytochrome-
b (951 base pairs [bp]), ND2 (1,013 bp), and ND3
(332 bp) genes, and from the nuclear introns 5
(528 bp) and 7 (939 bp) of the beta fi brinogen
gene, were collected from the holotype (PNSD
228) and analyzed phylogenetically with
sequences from other currently recognized spe-
cies of Thamnophilus. Missing were some of the
recently elevated forms of T. punctatus (Isler et
al. 1997). Detailed methodologies on molecu-
lar data collection and analysis are available
from R.T.B. or can be found in a forthcoming
publication on the molecular systematics of
Thamnophilus antshrikes.
F. 3. Sound spectrograms of the three principal vocalizations recorded for Thamnophilus divisorius.
(A) Typical male loudsong showing high-intensity terminal note. (B) Unmodulated two-note call, which is also
given singly. (C) Unmodulated caw call with pronounced harmonics.
W, O,  B
1038 [Auk, Vol. 121
A Bayesian analysis (Huelsenbeck and
Ronquist 2001) of the combined data using a
GTR+G+I model resulted in 100% support for
a sister relationship between T. divisorius and
T. insignis, a restricted-range species found
in the tepuis of southern Venezuela, Guyana,
and northern border regions of Brazil (Zimmer
and Isler 2003). Those two species form a well-
supported clade with T. amazonicus, which
occurs in lowland forest habitats, almost exclu-
sively in blackwater and clearwater drainages,
through most of the Amazon basin and Guianan
shield (B. M. Whitney pers. obs.). The relation-
ship was also found in the most likely tree (–ln
L = 6357.9) from a heuristic search of the com-
bined data using a GTR+G+I model (Swoff ord
2003). Although the tissue samples of T. amazo-
nicus (from eastern Santa Cruz, Bolivia) and T.
insignis (from Cerro de la Neblina, Amazonas,
Venezuela) were collected at points distant from
type localities of those taxa, voucher skins were
examined; we are confi dent that they provided
results that allowed accurate placement in the
phylogeny, even if they should be subject to
spli ing at the species level in the future.
Thamnophilus divisorius, isolated in the Acre
Arch ridge system and widely disjunct T. insig-
nis, on the slopes of tepuis, have undergone a
high degree of diff erentiation. Raw sequence
divergence at cytochrome-b between T. diviso-
rius and T. insignis was 7.9%; their sister rela-
tionship is thus rather distant. Morphology and
vocalizations in T. divisorius, T. insignis, and T.
amazonicus are not very helpful in recovering
relationships, especially in regard to T. divi-
sorius. However, the three species have main-
tained one common characteristic: all occupy
structurally and physiognomically similar
habitats that have especially nutrient-poor soils.
The ability of ancestral stocks to colonize these
oristically impoverished habitats (ridge forest
in Acre, melastome-dominated woody scrub
forest on the slopes of tepuis) has, in the case of
the T. amazonicus clade, led to marked diversifi -
cation at the species level.
Conservation.—The entire known popula-
tion of T. divisorius is offi cially protected in the
PNSD. The park encompasses one of the most
biologically diverse areas on Earth. It covers a
vast region (605,000 ha) and is located in the
middle-western sector of upper Amazonia,
including much of the Acre Arch uplands.
Because PNSD comprises a remarkable diversity
of forest habitats, it may help elucidate the spe-
ciation of many birds and mammals in particu-
lar, and the evolutionary history of Amazonian
habitats in general. And because of its location
in this region of Amazonia, PNSD contains for-
ests and rivers that are important for migrating
and overwintering birds from both the northern
hemisphere (including Central America and
northern South America), and from breeding
areas well to the south in Bolivia, Paraguay,
and Argentina. Unfortunately, however,
PNSD includes only the le bank of the Rio
Juruá. Because the river could prove to be an
important barrier to genetic exchange between
populations of birds and mammals (as are many
other long rivers in the Amazon basin), the park
should be expanded to encompass all represen-
tative habitats on the right bank of the river. For
example, populations of the saddleback tama-
rin (Saguinus fuscicollis) and monk saki monkey
(Pithecia monachus), both highly distinctive
primates with sister-taxon replacements across
the middle-upper Juruá, are unprotected east
of the river.
Several important challenges must be met if
PNSD is to maintain its integrity. All have to do
with pervasive and increasing manmade altera-
tions to the forest and rivers. These alterations
include subsistence practices such as clearing
of forest for homesteads and cultivation of food
crops, raising of livestock, and hunting, which
have been going on for decades in some areas.
Although subsistence activities have steadily
degraded the resources over the years, com-
mercial practices have a more immediate and
devastating potential. Those practices include
wholesale timber extraction, hunting with
trained dogs and highly skilled trackers for
commercial sales in population centers such as
Cruzeiro do Sul, gold mining, capture of parrots
and other birds and mammals for the pet trade,
and smuggling of narcotics and contraband
from Peru.
Several hundred families live within the
borders of PNSD, mostly along the rios Juruá,
Azul, and Moa. Plans for relocating the resi-
dents to areas outside the park boundaries are
underway, with orientation from the Brazilian
National Colonization and Agrarian Reform
Agency (INCRA). The fi rst station for monitor-
ing the park is being built and will be manned
by local residents. These initiatives and the full
implementation of the park’s management plan,
New Antshrike from Acre, BrazilOctober 2004] 1039
including an ecotourism component, lead us to
be optimistic about conservation prospects for
the region’s extraordinary biodiversity.
A
Our most sincere thanks to V. Passos, M. Scarcello,
F. Figueiredo, L. Honigmann, and D. C. Pimentel
Neto for help in working in Parque Nacional da
Serra do Divisor. We thank IBAMA-Brasília for spe-
cial collecting permits issued to D.C.O., whose work
was supported in part by a fellowship from CNPq.
We are grateful to P. Schneider, E. Gonçalves, and
M. Silvanira Ribeiro Barbosa of the Laboratório de
Polimorfi smo de DNA, Departamento de Genética
at the Universidade Federal do Pará, Belém, Brazil
for collecting the DNA sequences of T. divisorius; and
to A. Aleixo for his valuable assistance in seeing this
work through to completion. Molecular analysis was
supported in part by National Science Foundation
(NSF) grants DBI-9974235 and DEB-0332093 to R.T.B.
The editors of The Auk were most patient as we col-
laborated with Brazilian colleagues over a period of
several months. Frozen tissues of Thamnophilus insig-
nis (prepared by J. P. O'Neill) and T. amazonicus (pre-
pared by D. C. Schmi ) were provided by the Genetic
Resources Collection of the Louisiana State University
Museum of Natural Science. We thank F. de Lima of
the MPEG for help in working with the specimens of
the new antshrike, and T. Schulenberg for examining
the voucher specimen of T. insignis from Cerro de la
Neblina for us. M. H. Matsumoto of the GIS depart-
ment of The Nature Conservancy in Brazil kindly
prepared the satellite image (Fig. 1). The manuscript
benefi ed from the thoughtful comments of M. and
P. Isler, P. Stouff er, and two anonymous reviewers.
Finally, we are greatly indebted to L. McQueen for his
magnifi cent illustration of the new species.
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Associate Editor: P. C. Stouff er
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