 The
Antbirds are a large family confined to the Neotropics. The vast majority
are birds of lowland forests in which they have adapted to niches ranging
from dense thornscrub to steaming Amazonian jungle. They are all small
to mid-sized predators, eating insects and arthropods. Almost all are plumaged
in various shades of black, gray, or rufous; most are strongly sexually
dimorphic. This Rusty-backed Antwren (left), so brilliantly
photographed by Simon Woolley & Julia Casson, is a male with
black throat and breast, fringed all around with white, with rusty upperparts
and tail, and black-and-white patterned upperwing coverts. Females have
a black-and-white streaked throat and breast. This species lives in pairs
in dense undergrowth in a large swathe of southern Brazil, and locally
elsewhere. Pairs communicate with loud, diagnostic songs.
Unlike other suboscines about which there is much confusion over the boundaries between families (particularly in the cotinga-manakin-flycatcher sets), the Antbirds are a well recognized and well defined group once it became clear that the ground-antbirds [Formicariidae], containing the antpittas and ant-thrushes, were a different family. The remaining Antbirds are a monophyletic group, and it is easy to determine what is and what is not an antbird. Almost all species are monogamous with evidently permanent pair bonds; they are rather amazingly constrained in pattern and color combinations and most have similar bill shapes, with little variation among the 200+ species; their diet is almost exclusively arthropods; the elevational distribution is very truncated, with few species occurring above ~1300 m, and most are lowland birds below 600 m elevation. It seems remarkable that a family that shows such restrictions contains so many species. Their species richness is associated with extreme habitat and foraging specialization, themes that are developed a bit more below. Much is being learned about antbirds currently, and new species are discovered, or elevated from previously lumped groups, at a rapid pace, even among authorities strictly conforming to the biological species concept. For example, Sibley & Monroe (1990) listed 188 species of antbirds. A dozen years later, Dickinson (2003) listed 206 while Zimmer & Isler (2003) tallied 209 species. I use the latter list as the most current and definitive. This is an addition of 21 species in the last 13 years and illustrates how rapidly new information is being gathered in South America (more on this story is also below). |
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 The
first European naturalists to encounter New World antbirds confused them
with Old World groups, and particularly they confused them with shrikes
[Laniidae] because of the heavy, hooked bill of some species. It wasn't
until 1847 when German anatomist J. Müller discovered that the syrinx
of a number of New World groups, including antbirds, was very different
than Old World groups that things began to be sorted out (Zimmer &
Islet 2003). Yet the names remain, comparing species in the Thamnophilidae
with species in other unrelated groups. Of the 209 species in Zimmer &
Isler (2003), some 67 species are called Antwrens and 50 species are termed
Antshrikes. Smaller groups are Antvireos (8 species in genus Dysithamnus),
three enigmatic Bushbirds (in 2 genera), three Fire-eyes (Pyriglena),
and two Bare-eyes (Phlegopsis).
The Antshrikes might be the most conspicuous because of their sometimes aggressive behavior, their rollicking calls, the conspicuous crest on some species, and their largish size for this family. They are scattered among 14 genera. The striking Silvery-cheeked Antshrike (right, in a nice shot by Arthur Grosset), is in the genus Sakesphorus, a group of mid-sized antshrikes scattered around South America, usually restricted to understory habitats. Sexual dimorphism is great in this group, with males tending toward more blacks and grays, and females sporting more rusty tones. The most common English name, though, is Antbird. Some 76 species in 17 genera bear this moniker. As a group, most antbirds are ground-dwelling mystery birds or undergrowth skulkers. I find these types of the bird particularly fascinating. Just one example is Spot-backed Antbird (below in a spectacular shot by Arthur Grosset), a widespread species on the Amazonian understory, generally preferring upland or terra firme forest. Zimmer & Isler (2003) say it is "often near treefall light-gaps with extensive low growth, bordering areas of shaded, open understory with abundance of thin vertical saplings." How's that for a specialized niche? But note that while they state this antbird may be "near" a light-gap, on the whole the understory antbirds are "photophobic, shunning even small patches of sunlight" (Zimmer & Isler 2003). No wonder seeing antbirds can be a real challenge! |
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| The most fascinating group of Antbirds may be the dedicated ant-swarm
followers. These are antbirds that follow "army-ants" [subfamily Dorylinae]
and especially the widespread Eciton burchelli, "a diurnal swarm raider,
fanning out along broad fronts containing hundreds of thousands of ravenous
carnivorous ants. In the process, these flush large number of arthropods
and small vertebrates, many of which are normally concealed in leaf litter.
Ahead of the swarm await opportunistic birds and parasitic wasps and flies,
ready to pounce on potential prey or hosts fleeing the ants. The birds
do not eat the ants... rather, the army ants provide an important service
that greatly increases foraging efficiency... the bird allow the ants to
act as 'beater,' which drive an abundance of prey right into their laps;"
Zimmer & Isler (2003). Nothing cheers the heart of a neotropical birder
like finding an active swarm of army ants on the forest floor, attended
by many bird species. Some 18 species in seven genera are considered "obligate"
ant followers, which are almost never found away from the ants. Among the
obligate ant followers, only the three fire-eyes (genus Pyriglena)
are known to forage away from ants. Beyond the 18 "obligates," another
six species in four genera are regular ant-followers but can be frequently
found away from the ants.
The ant-followers are especially evolved to sit "sideways" on vertical saplings above the ant swarms on the forest floor [woe to that bird that itself gets trapped by the ants!... they'll eat anything]. So the specialized antbirds forage just above or in front of the ants, snapping up prey from their vertical perches. Here are two nice shots that illustrate this unique stance: a Scale-backed Antbird (below left, taken by Bob Tintle in southeast Peru during our trip their in 1987) and a Bicolored Antbird (below right, taken by Arthur Grosset in Brazil). The Scale-backed is one of the six "regular" ant-followers but the Bicolored is an obligate ant-follower, virtually never found away from the ants. |
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| I admire the photographers who've managed to shoot pictures of the photophobic antbirds. Obviously, flash is a necessity, and is not a technique with which I have much experience. Indeed, my own photos of any species in this huge family are rather marginal, but I show a couple below to illustrate another point. Here are two antshrikes. One of them, Barred Antshrike (below right) has perhaps the widest range of any of the family, occurring from southern Mexico (this shot) to northern Argentina. Zimmer & Isler (2003) recognize a dozen races. It is a common and well-known bird; the one here is a young male. The other, Collared Antshrike (below left; a male), is specialized. It occurs only in the understory of dry, deciduous woodland in coastal northwest Peru and west Ecuador. But even it has two races; many species of antbirds are exceptionally local and specialized. | ||
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 It
is often those rare and specialized antbirds that capture our attention
as world birders. Slender Antbird, a female of which is so beautifully
shown in this Arthur Grosset shot (right), is found only
locally in two states in eastern Brazil, among a specialized habitat known
as mata-de-cipó — understory of remnants of hillside deciduous
forest with many lianas [cipiós] and high precipitation.
This restricted range species is considered Endangered (Birdlife International
2000).
I've been fortunate to have a few experiences with antbirds that were rare, local, little-known or undescribed to science. When Rita and I visited La Selva Lodge in eastern Ecuador in Apr 1992, we made a special effort to search out the very scarce and local Cocha Antshrike Thamnophilus praecox, a bird that still appears to be restricted to limited black-water thickets in the Rio Napo drainage of northeast Ecuador. Our local guide Fausto, although he spoke very little English, knew exactly where it would be. We were able to return the favor when we discovered a Black Bushbird Neoctantes niger on a day's hike into the terra firme forest; it was an entirely new bird for Fausto, despite years of guide services. We had great views as it hammered and probed the viney thickets with its unique bill. In the most compelling category, though, was an all-black Cercomacra antbird that had just been discovered by LSU researchers at Explorer's Inn, Tambopata wildlife reserve, Made de Dios, Peru, a few months before our visit there in summer 1987. It was exciting enough that there were "bamboo specialists" that we saw right near the lodge, such as Bamboo Antshrike Cymbilaimus sanctaemariae [proven to be a separate species only a couple years before our visit; Pierpont & Fitzpatrick 1983), but upon arrival we learned that a "new Cercomacra antbird" had been discovered in Guadua bamboo thickets across the Madre de Dios River. We were able to copy a tape with its odd duck-like quacking call, and bum a ride across the river one afternoon. With some good luck and tape-playback, my friends and I got good looks at the new species — the first time I'd ever seen "a bird with no name," to wit, a species yet unknown to science. This was thrilling, even if I had nothing to do with the discovery, and I was able to make my own tape of the bird, thus having in hand a unique tape of an undescribed species. The species was described by Fitzpatrick & Willard (1990) as Cercomacra manu, the Manu Antbird. Its range has now been found to be much broader than southeastern Peru, as it is patchily scattered across southern Amazonia and appears to be fairly common locally (Zimmer & Isler 2003). Indeed, I would encounter it a dozen years later along the Rio Cristalino in central Brazil. But there is nothing quite like the experience of being one of the first few non-native observers to see a bird in the wild. |
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 Yet
another part of the fascinating story of antbirds is their part in the
mixed-species flocks in the Neotropical lowland forests. There are canopy
flocks, mid-story flocks, and undergrowth flocks, often composed of 25-50
individuals of 10-30 species. Antwrens are particularly common in the upper-level
flocks, and often the 'core' species is an antwren. It is not unusual to
have a half-dozen antwren species in a good Amazonian forest flock. One
example, mostly limited to white-sand forests of upper Amazonia and thus
rather little known, is Cherrie's Antwren (left, in another
great Arthur Grosset photo). Another example from upper Amazonia,
but on borders of taller, primary, virgin lowland forest, is Moustached
Antwren (below, in my own very marginal photo). Back when I
took this shot in 1987, it was known as "Short-billed Antwren Myrmotherula
obscura" and its actual relationships were not sorted out until recently
(see Zimmer & Isler 2003).
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 When
my little party of California birders visited Explorer's Inn in southeastern
Peru in 1987, we came upon researcher Ken Rosenberg, then working on post-graduate
studies. He was studying "dead leaf gleaners" — most of them antwrens but
also some antshrikes and birds from other families — in a broadscale conceptual
project that had first been proposed by Van Remsen and Ted Parker (e.g.,
Remsen & Parker 1984). In an evergreen forest of broadleaf trees, there
is always an abundance of hanging dead leaves. These are perfect places
to hide nocturnal foragers during the day. What the LSU researchers found,
including in the studies eventually published by Rosenberg (1993, 1997),
is that specific antbirds rely heavily on dead-leaf-foraging for their
livelihood. Many search the dead leaves for anything hidden inside while
moving with a mixed species flock. They are hanging upside down and peering
into clusters of dead leaves while others in the flock are searching branches
or live leaves. Some species are "obligate" dead-leafers, with 99% of their
prey taken that way. Examples include Ornate Myrmotherula ornata
and White-flanked M. axillaris Antwrens, and probably all the members
of the "stipple-throated antwren" group. Other species are "regular" dead-leafers;
an example is the widespread Warbling Antbird (right), in
yet another fabulous Arthur Grosset shot — note the dead leaf attached
to the branch being used by the hungry antbird! There are 10 named races
of Warbling Antbird; this particular bird is H. c. peruviana from
e. Peru, s.w. Brazil, and n.w. Bolivia. The studies cited (Remsen &
Parker 1984, Rosenberg 1993, 1997) show that Warbling Antbird is a "regular"
but not "obligate" user of the dead-leaf resource, with 31% of foraging
observations in this unique substrate.
The evolution of antbirds into a multiple of niches characterized by mixed species flocks, and army ant followers, and dead-leafers, and much more, has been a lifelong study by famed ecologist E.O. Willis. He has published many papers on a host of topics just brushed upon here; for example, army ant following (Willis & Oniki 1978) or specific information on the endangered Slender Antbird (Willis & Oniki 1981). The study of antbirds is a rich field, and there is so much more to learn. Even the basic biology of many species has yet to be studied (just look how many times the words "not known" or "little known" appear in Zimmer & Isler (2003).... |
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| Photos: Simon Woollsey & Julia Casson photographed
the Rusty-backed Antwren Formicivora
rufa on 10 Aug 2002 in the Pantanal of Brazil. Arthur Grosset
photographed the Silver-cheeked Antshrike
Sakesphorus cristatus at Chapada Diamantina, Bahia, Brazil, in July
2002; the Spot-backed Antbird Hylophylax
naevia along the Rio Negro at São Gabriel da Cachoeira, Amazonas,
Brazil, in August 2004; the Bicolored Antbird
Gymnopithys leucaspis was also at São Gabriel da Cachoeira,
Amazonas, Brazil, in August 2004; the Slender Antbird
Rhopornis ardesiaca at Boa Nova, Bahia, Brazil, in July 2002;
the Cherrie's Antwren Myrmotherula
cherriei at São Gabriel da Cachoeira, Amazonas, Brazil, in August
2004; and the peruviana Warbling Antbird
Hypocnemis cantator was on Peruvian side of the Rio Javari in Sep 2003.
Robert F. Tintle photographed the Scale-backed
Antbird Hylophylax poecilonota at Tambopata Nature
Reserve, Madre de Dios, Peru, in June 1987. My photo of
Collared Antshrike Sakesphorus bernardi was in the
Chongon Hills, west Ecuador, on 5 Oct 1989; that of
Barred Antshrike Thamnophilus doliatus was at Sumidero
Canyon, Chiapas, Mexico, on 19 Mar 2002; and the Moustached
Antwren Myrmotherula ignota was at Sucasari Camp on
the Rio Napo, Loreto, Peru, on 9 June 1987.
Photos are
© 2004 Simon Woolley & Julia Casson, Arthur Grosset, Robert F.
Tintle, and Don Roberson, as indicated; used with permission, all rights
reserved.
More evocative shots from Simon Woolley's and Julia Casson's world birding trips are on their web site [see particularly their Brazil travel diaries], and many more outstanding Arthur Grosset photos are on his web page (he particularly features South America). Arthur has a large and growing catalogue of photos of South American species, many of them rarely (if ever) photographed in the wild before. Family Book: There is no family book per se, although some behavioral texts have used antbirds as examples of important principles. I had long heard that E.O. Willis was working on a family book but either it came out and I missed it, or (perhaps) he is still at work on it. Thus the summary by Zimmer & Isler (2003) in the Handbook of the Birds of the World series was, for me, a long-awaited and much-anticipated publication, and I found it to be excellent, not to mention all the sumptuous photographs found therein! Literature cited: Birdlife International. 2000. Threatened Birds of the World. Barcelona & Cambridge, U.K., Lynx Edicions & Birdlife International. |
