Olson • THE EXTINCT HAWAIIAN GENUS CIR1DOPS 
665 
M. flexor hallucis longus. —Only the origin of 
the medial head remained. This appeared to be 
exceptionally strongly developed, more so than in 
VC or HS. and the more expanded distal end of 
the femur would have acted to provide increased 
area for attachment of this muscle. 
Discussion of Myology 
Almost all of the thigh muscles of Ciridops 
were markedly better developed than those of its 
nearest relatives Vestiaria and Himatione. These 
muscles are mainly those involved in moving the 
femur or holding it in position, although one is 
involved in flexing the hind toe, all of which 
indicate a much more vigorous use of the 
hindlimb than in related species. 
Functional Interpretation of Hindlimb Anatomy 
and Morphological Analogs of Ciridops 
The pelvis and hindlimb structure of Ciridops 
diverge significantly from those of all other 
Drepanidini. including especially its presumed 
closest relatives (Vestiaria and Himatione). All of 
the hindlimb elements are much more robust but 
this is most evident in the exceptionally short, 
stout femur. The pelvis is correspondingly 
modified to accommodate the much more strongly 
developed musculature of the thigh. This indicates 
active use ol the hindlimb in some activity other 
than simply perching or hopping from branch to 
branch (or along the ground), which arc probably 
the only major uses of the hindlimb in other 
drepanidines. 
Therefore, to hypothesize the activity in which 
Ciridops may have been engaging it is necessary 
to identify other passerines with similar adapta¬ 
tions of the pelvis and hindlimb, particularly the 
femur. The most extreme adaptations of this 
nature are found in the chowchillas (Orthonyx), 
which occur in woodlands of Australia (familial 
level relationships of Orthonyx . as well as 
Bowdleria and Mohoua. are still unresolved, 
although they are not closely related to one 
another). The femur in Orthonyx is extremely 
short and stout, appearing almost like that of a 
loon (Gaviidae) and quite unlike that of most 
other passerines (Olson 1990b. Boles 1993). 
These birds have a specialized foraging behavior 
in which one foot is used as a brace and the other 
for vigorously scratching and removing forest 
litter in a search for prey (Zusi 1978). Another 
group with similar, although less extreme mor¬ 
phological and behavioral adaptations are the 
New Zealand fernbirds of the genus Bowdleria 
(Olson 1990b), which also use the hindlimb not 
only to scratch and push away detritus but also to 
pick up leaves with the feet (Rest 1979). Both 
Orthonyx and Bowdleria are almost completely 
terrestrial, however, which is unlikely to have 
been the case with Ciridops. 
A much better analog for Ciridops are the two 
more specialized species of the New Zealand 
genus Mohoua. the Whitehead (A7. alhicilla) and 
Yellowhead (A/, ochrovephala). These are medi¬ 
um-small arboreal birds with a short bill with a 
curved culmen that compares quite favorably in 
overall shape with that of Ciridops, and with 
large, strong feet. The pelvis and hindlimb are 
specialized along the same lines as those of 
Ciridops with the femur in particular being 
notably short and stout (Olson 1990a). The 
Yellowhead feeds in treetops but also roots 
“through the accumulations of rubbish that fall 
down and collect” in the forks of trees, at which 
time they grip with one foot, use the tail as a prop, 
and “scratch vigorously with the other foot, 
sending down a shower of debris” (Soper 1976: 
50). 
The claimed close association between Ciri¬ 
dops anna and loulu palms ( Pritchardia) is 
perhaps best explained not by the bird eating the 
fruit or any other part of the palm itself, the fruits 
usually being much too large for a bird the size of 
C. anna to process, but by the birds finding food 
among the litter that accumulated in the axils of 
the palm leaves. This 'rubbish’ was presumably 
moved by the bird’s using its large and well¬ 
muscled feet and legs to expose invertebrates 
hidden within the accumulation. 
That the crowns of Pritchardia palms (Fig. 7) 
act to accumulate debris has been observed in the 
field by botanist C. D. Bacon (in litt. 14 Dec 
2011 ): 
“First are things that get trapped in the 
crown—seeds, leaves, and debris from other 
plants, small herbaceous plants and mosses, 
and invertebrates, anything you can imagine 
falling from other plants or the sky into a plant. 
The second contribution is from morphological 
attributes of the crown itself—the upper sides 
of the leaf sheath and petiole are often very 
fibrous and sometimes pubescent with dense, 
woolly hairs. These fibers and hairs more often 
than not, split off and break at the margins, and 
fall into the crown and might also offer easy 
