Recent Research on the Anodorhynchus Macaws Feeding Habits

Abstract

Until very recently, little was knovrn
about the feeding habits of the Anodorhynchus
macaws . The earliest
detailed references I have found on
their feeding habits both occur
in H.W. Bates' The Naturalist on the
Amazons, first published in 1863
about his 11 year sojourn in Brazil.
In the chapter entitled "The Tocantins
and Camera", his entry for 7th
September, 1848 includes the following:
"We saw here, for the first time,
the splendid Hyacinthine Macaw
(Macrocercus hyacinthinus, Lath., the
Araruna of the natives), one of the
finest and rarest of the parrot family
.... It flies in pairs, and feeds on the
hard nuts of several palms, but especially
of the Mucuja (Acrocomia lasiopatha).
These nuts, which are so hard
as to be difficult to break with a heavy
hammer, are crushed to a pulp by the
powerful beak of this macaw."
Four years later in describing the
"Voyage up the Tapajos", he wrote,
"The Macaws were found feeding in
small flocks on the fruit of the Tucuma
palm (Astryocaryum tucuma), the
excessively hard nut of which is
crushed into pulp by the powerful
beak of the bird. I found the craws of
all the specimens filled with the sour
paste to which the stone-l ike fruit had
been reduced."
For the next 125 or mo re years there
does not appear to have been much
added to these two pieces of information.
Goeldi , in his As Aves do Brasil of
1894, appears to have transferred the
feeding habits of the Hyacinthine
Macaws described by Bates to the
Glaucous Macaw (Anodorhynchus
glaucus) and this was then repeated
by Helmut Sick in his great work
Ornitologia Brasileira of 1984.
In the last few years, research carried
out by Munn, Yamashita, Brandt
and Machado has confirmed Anodorhynchus
macaws to be special ist
palm-nut feeders. In our own visits to 

the Pantanal in Brazil, we have observed
the Hyacinthine Macaws feeding
off " acuri" palms (Scheelea or
Attalea phalerata) and "bocaiuva"
palms (Acrocomia aculeata).
In my report in the ovember 1992
issue of the Parrot Society Magazine
("The Glaucous Macaw. Does it Still
Exist?") on our visit to Argentina, Paraguay
and Brazil to investigate the
extant habitat of the Glaucous Macaw,
I related how Joe Cuddy and I speculated
from numerous historical references
to the flora of the region that the
Glaucous Macaw fed exclusively off
the palm nuts of the yatay palm (Butia
yatay) and had become extinct 

because of clearance of the yatay
palm groves throughout its distribution
area.
This has now been confirmed in an
article by Carlos Yamashita and Mauro
de Paula Valle published in the April
1993 issue of the BOC Bulletin. In this
article, the authors compared the bill
cu tting action and efficiency of the
Anodorhynchus macaws, which
specialize in palm nuts , and o ther
members of the parrot family, which
are not such specialists.
The Anodorhynchus macaws are
known to have the strongest chisel
action with the lower mandible of all
the parrot family. Both the Hyacin-

thine and the Lear's Macaw use the
cutting edge of the "chisel" to split
palm nuts in two. It would appear
logical to assume that the Glaucous
Macaw, as a member of the Anodorhynchus
genus, shared this characteristic.
For their study, Yamashita and de
Paula Valle measured the chisel width
of all three Anodorhynchus species as
well as that of 13 other parrot species
in museum skin collections. They also
collected palm nuts opened by different
species of macaws to compare the
cutting pattern.
The mean chisel width size for non
palm-nut specialists ranged between
7.4 mm for the Red-shouldered or
Hahn's Macaw (Ara nobilis) to 15.4
mm for the Green-winged Macaw
(Ara chloroptera). The Anodorhvnchus
macaws had a much larger chisel
width with a mean of 22.4 mm for the
Lear's Macaw (A. leari) 24.2 mm for
the Glaucous Macaw (A . glaucus) and
30.6 mm for the Hyacinthine Macaw
(A. hyacinthinus). The authors also
discovered that body size does not
correlate to chisel width . The Redfronted
Macaw (Ara rubrogenys), for
example, is smaller than the Blue and
Yellow Macaw (Ara ararauna), but
has a wider chisel width. The Lear's
Macaw, Blue and Yellow Macaw and
Scarlet Macaw (Ara macao) are similar
in size and weight, but have very
different chisel widths with a mean of
22.4 mm, 11.3 mm and 12.2 mm
respectively. Some conures have ve1y
wide chisel widths in relation to their
size.