Plumages, Molts, and Structure

Descriptions of Maui 'Akepa hampered by small number and great age (100–170 yr) of specimens (Figure 9 ). Below are descriptions are of Hawai'i 'Akepa captured at Hakalau Forest NWR by JKL (unless otherwise noted), which are presumably similar. Capitalized, numbered colors were matched to Smithe 1975 .

Hatchlings

Mostly naked at birth, with some dark gray down, close to Smoke Gray (45) on spinal and capital tracts (see also Breeding: Young Birds).

Juvenile Plumage

Juvenile plumage pale Olive-Green (47) or Grayish Olive (43) above, pale gray to Cream (54) below, mottled with Smoke Gray (45), heaviest on breast. Face pale gray, often with whitish superciliary line. Occasionally has whitish forehead or dark median crown-stripe. Remiges, wing coverts, and rectrices dark brown, similar to Fuscous (21) or Olive-Brown (28), edged Olive-Yellow (52) to Straw Yellow (56). Some birds have Olive-Yellow (52) shoulders and sides of breast and flanks. Feathers of belly and vent looser and fluffier than Basic I plumage. Sexes similar. Museum specimens from Maui similar, but possibly average darker; a specimen from Maui had remiges and rectrices edged closest to Raw Sienna (136) or Cinnamon (123A).

Basic I Plumage

Basic I plumage similar to Juvenile plumage, but without the looser feathers or Olive-Yellow (52) color, and supercilium less prominent. Wing-coverts dark brown, frequently edged Olive-Green (46) or Bunting Green (150), which usually wears off before Prebasic II molt. Remiges and rectrices dark brown, edged Olive-Yellow (52) to Straw Yellow (56), frequently turning pale gray by Mar of second year (observed on recaptured individuals), probably because of fading and/or wear and abrasion. Sexes similar. Distinguished from duller adult females by lack of yellow or orange wash across breast.

Basic II Plumage

Male. Half to three-fourths orange, ranging from bright Chrome Orange (16) to duller, browner hues such as Pratt's Rufous (140), Burnt Orange (116), Cinnamon Rufous (40), and Ferruginous (41). Remiges, wing coverts, and rectrices dark brown, edged various shades of orange, usually dull, but occasionally as bright as Chrome Orange (16). Most of underparts, including crissum, vary from pale creamy to bright orange. Brightest orange feathers mostly on face and breast, less often on rump. Crown, nape, and back usually duller, browner orange. Patches of gray green feathers often remain on back, nape, and crown, and appear to be at least partly due to retained feathers of Basic I plumage, on basis of degree of wear.

Female. Similar to Basic I birds, but some show trace of pale Orange Yellow (18) or Spectrum Orange (17) breast-band. Others entirely gray above, paler below, with no green or yellow. Females distinguished from Basic I birds by lack of supercilium, lesser degree of feather wear on remiges and rectrices, greater degree of feather wear on nape, and bill color.

Definitive Basic Plumage

Maui 'Akepa males (Figure 9 ) show color dimorphism: 45% reported as dull Chrome Orange (16), 45% Spectrum Yellow (55) with a tinge of Olive-Yellow (52), and 10% intermediate (Pratt 1989 ). Specimens examined by JKL were either Spectrum Orange or Yellow Ocher (123), and none were as bright as reported by Pratt (1989 ). Maui 'Akepa females similar to females of Hawai‘i 'Akepa, but duller and without orange.

No information on molts for Maui 'Akepa. Below are descriptions are of Hawai'i 'Akepa captured at Hakalau Forest NWR by JKL (unless otherwise noted), which are presumably similar. Capitalized, numbered colors were matched to Smithe 1975.

Prejuvenile Molt

Prejuvenile molt poorly known. No Juvenile feathers present on day 4, but chicks appeared fully feathered by day 12 (JKL).

Prebasic I Molt

Prebasic I molt partial; occurs Jun through at least Oct (no Nov or Dec captures), with small amounts of molt continuing on crown and nape through Feb (JKL). Molt includes body feathers, but remiges and rectrices retained.

Prebasic II Molt

Prebasic II molt almost complete; includes remiges and rectrices, but males and possibly females may retain worn Basic I body feathers, particularly on back, nape, and crown (JKL). Males begin to molt on face and sides of breast as early as Mar, continuing with full molt through Oct. Females molt from Jun through Nov. Some individuals molt all rectrices at once, resulting in distinctive tail-less appearance.

Definitive Prebasic Molt

Definitive Prebasic molt complete in both sexes; occurs from Jun through Oct (Figure 6 ). Molt begins after offspring leave nest, but before they become independent. Prebasic molt generally begins and ends on body. Females have low levels of body molt through Nov, and some individuals have a few straggling feathers coming in on crown and nape through Apr (JKL). Primaries molt in order from P1 to P9 (JKL), like other Hawaiian honeycreepers. Secondaries probably conform to general drepanidine pattern of S8, S9, S7, S1–S6 (Baldwin 1953 ), and may finish molting shortly before or after primaries. Tail molt usually finishes before remigial molt; some individuals molt all rectrices simultaneously.

Bill And Gape

Bill notable for lateral asymmetry: Tip of lower mandible curved to right or left, resulting in slightly skewed tips (Figure 2A and B ). Lower mandible curved to right in 16 of 27 Maui males (59%) and 5 of 13 Maui females (38%); tendency for bill to cross to right not statistically significant (Hatch 1985 ).

Bill asymmetry due primarily to differences in horny ramphothecae; some asymmetry occurs in bones and muscles of jaw and skull (Richards and Bock 1973 , Knox 1983 ). Mandibular ramphotheca is wider, flatter, and higher on side to which lower mandible is curved, and muscles are larger on that side of head (Richards and Bock 1973 ). Muscles also have modified fiber arrangement to provide greater force; some are estimated to exert up to 100% more force than corresponding muscles on opposite side of head (Richards and Bock 1973 ). Asymmetry of muscles and bones allows bird to exert greater lateral force to pry open leaf and flower buds. Juveniles at Hakalau Forest NWR show little or no lateral curvature of lower mandible, agreeing with Perkins (1903 ) and Hatch (1985 ), but contrary to Henshaw (1902 ). Ontogeny of asymmetry not known. Horny palate has generalized pattern of ridges and troughs similar to that found in emberizid sparrows and differs markedly from those of finch-billed Hawaiian honeycreepers (Koblik 1994 ).

Bill color variable among Hawai‘i 'Akepa adults, ranging from horn or Pearl Gray (81) to Straw Yellow (56) or pale orangish. This variation appears not to be age-related, on basis of banded individuals followed for up to 5 yr, although 1 individual changed from orangish to horn color over period of 4 yr (JKL). All adults have dark bill-tip. Juveniles have mostly brownish bills, which are noticeably stubbier (shorter and blunter) than those of adults, often with orange cutting edges; and brown color remains longest on ridge of culmen. Bill of Maui 'Akepa adults reported as Pearl Gray (81); some have darker tips (Pratt 1989 ). Gape ranges from pink to red.

Iris And Orbital Ring

Iris dark brown, appearing black except under bright light in hand. Orbital ring black

Legs And Feet

Black. Pads of toes gray.

See Appendix 1 and Appendix 2 . No mass data available for internal organs. Knox (1983 ) noted an asymmetry in legs of Hawai'i 'Akepa, tarsus averaging 0.15 mm longer on the side opposite to which the mandible crosses, presumably because of "handedness" in holding leaf and flower buds when opening them with asymmetric bill. This asymmetry likely occurs also in the 'Akepa species.