Consideraciones Sobre Conserv. de Pluma y Pelo

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fur trade legacy workshop 127

AbstractFeathers are amongst the most complex epidermal derivatives found in vertebrates.

They have complex branched structures, grow from their bases by a unique mecha-

nism, and come in a wide variety of sizes, shapes, structures, and colours. Not

only do feathers impart cover, insulation, waterproofing of the body, contribute to

flight, tactile sensations or protection of sensory organs, even storing water, they

are also involved in myriad aspects of communication and display in birds, and

characteristically rather ornately. Underlying this diversity of colours and patterns

found in birds is a variety of pigments (melanins, carotenoids, psittacofulvins, por-phyrins, etc.), pigment-bearing structures and molecules, and complex micro- and

macrostructures.

Given the great structural and functional diversity of feathers it should come as

no surprise that their conservation should require a multifaceted approach. Accord-

ingly, a brief review of feather anatomy, including the arrangement of feathers on

the skin (pterylosis), chemical composition, even the native fauna of feathers (e.g.,

lice, mites, bacteria)will be provided, emphasizing aspects of feathers that may be of

relevance to conservators.

Since cleaning methods are well covered by other speakers, my focus will be on

the preventive conservation of feather and fur colour from light. I will show howeven pigment systems that seem biochemically homogenous—like the melanins of

mammals—show surprisingly complex and species-specific responses to light. For

example, in pilot fading experiments, mink, but not marten, fur darkened initially

upon exposure to light. Attempts to quench free radicals likely generated by light

irradiation did not appear to slow fading down.

Considerations in the Conservation of Feathers and Hair, Particularly their Pigments

Jocelyn Hudon

Introduction

Feathers are among the most complex integumentary appendages foundin any vertebrate (Lucas and Stettenheim, 1972). They have complex

branched structures, grow from their bases by a unique mechanism

(Prum and Brush, 2002), and come in an astonishing variety of shapes,

sizes, structures, and colours.Feather follicles can alternatively form feathers of different types in

each skin area in an arrangement that is precisely determined to form a

coherent plumage that conveys information about the bearer’s species,age, sex, and, sometimes, even condition.

From their humble origins as structures that probably functioned in

defence, thermal insulation or water repellency (Prum and Brush, 2002),

feathers diversified into structures that provided cover, permitted activeflight, carried tactile sensation, protected sensory organs, produced

sound, and, even, stored water. More importantly, feathers became highly

patterned and ornate, involved in myriad aspects of display and commu-nication in birds, a highly visual group of vertebrates.

Perhaps not surprisingly, feathers have been repeatedly borrowed as

ornaments by another highly visual species, Homo sapiens, in countlesscultural settings and periods, at times incorporated into headdresses, dia-dems, cloaks, capes, wristbands, earrings, and sceptres, even European

fashion, notably millinery. Feathers have also been used in the fletching

of arrows, bedding, ornamentation in millinery, as quill pens, powder-

puffs, even the making of artificial flies for fishing.Feathers still attached to skin, like whole birds, whole skins and parts

of skins and bird’s bodies, are also represented in various collections

(Rae and Wills, 2002). However, the use of bird skins for practical pur-poses is less common, being strongest in cultures that were more reliant

on birds for their survival, like people of the Arctic, where the skins of



128 cac / accr 31st annual conference, jasper 2005

marine birds were used to make parkas, overslippers, stockings, bonnets

and bags (Oakes and Riewe, 1996). In those instances where mammalian

skins were available, they were usually preferred as more durable (Raeand Wills, 2002).

For an exposition on the conservation of feathered skins, as opposed

to the feathers themselves, the reader is referred to Rae and Wills(2002). Feathered skins are also of course widespread in natural history

collections.

Although, in a museum context, attack by insects, deposition of dust

and soiling, and poor storage conditions are the most damaging to arti-facts incorporating feathers, these topics are largely covered by other

speakers. My focus here will be to provide information on the “natural

history” of feathers and on the effect of light of these brightly-colouredintegumentary derivatives.

Feather Composition

Like the epidermal appendages of other amniotes (reptiles, birds andmammals), feathers are composed mostly of keratin(s), an intermediate

filament protein produced by epidermal cells that forms a hard, flex-

ible, and insoluble polymer (Brush, 1978a). Unlike the α-keratins of the

epidermis and the hairs of mammals, which naturally form α-helices,the keratins of feathers, scutate scales, claws and beak, rather adopt a

beta-pleated sheet structure, where hydrogen bonds are formed betweenadjacent parallel or antiparallel polypeptide strands, yielding a markedly different high angle X-ray diffraction pattern (Brush, 1978a).

The feathers, scutate scales, claws and beak of birds (and a few reptiles)

are composed of a subclass of β-keratins that are referred to as feather

keratins, orφ-keratins (Brush, 1978a). The keratins of feathers are poly-peptides of about 100 amino acid residues (Presland et al., 1989a, 1989b;

Takahashi et al., 2003), with a molecular weight of approximately 10.4

kD [one Dalton (D) is the mass of an atom of hydrogen]. Avian scutatescales, beak, and claw are composed of another subclass of filament-

formingφ-keratins that are slightly larger (13.4 kD). Theα-keratins arecomparatively much larger at about 56.5 to 60 kD.

Feather keratins are relatively high in glycine, serine, proline, leucine,

and glutamic acid. Acidic amino acids exceed the basis residues, and the

overall pattern differs quantitatively from other fibrous proteins (Brush,1978a). When compared to mammalian hair keratins, feathers have

relatively lower methionine and lysine and a higher proline content

(Brush, 1978a).

Feather keratins are produced by several families of closely relatedgenes, occurring as tandem repeats throughout the bird genome. It has

been estimated that there may be as many as 100-240φ-keratin genes in

the chick genome alone (Kemp, 1975).

The flexural stiffness of the rachis does not appear to be controlledby the material properties of feather keratins, but rather by their cross-

sectional morphology (Bonser and Purslow, 1995). The X-ray diffraction

pattern of the intact feather calamus indicates a high degree of crystal-linity which can be deformed by stretching and is affected by heating in

water or aqueous butanol (Brush, 1978a). Crooks in feathers can usually

be removed with a stream of water vapour (steam).Much of the following information about types, structures and

arrangement of feathers—including several illustrations—is taken from

Lucas and Stettenheim (1972).

Pterylosis

In most birds, but excluding ratite birds (kiwis, cassowaries, emu, rheas,

and ostrich) and penguins, feathers are not distributed uniformly over a

bird’s body, but rather segregated into tracts or groups, interspersed withfeatherless spaces over the body (Fig. 1).

The areas covered by contour feathers, which are visible on the exter-

nal surface of the plumage, are called pterylae (Fig. 1). The areas of theskin without feathers, or with only down or semiplume feathers, are

called apteria.




Pterylography, or more commonly pterylosis, describes the pattern

of feather tracts (or feather follicles) in birds, while ptilosis is used to

describe the plumage associated with these follicles.

Moult

From the time a bird hatches until it becomes an adult, its featheringpasses through several changes in appearance. These changes are due

largely to a periodic replacement of feathers. In most birds, the shape of

each feather is established during its growth and does not change there-after except through wear. All feathers of fully-grown birds are replaced

at least once annually by moulting, in a stereotypical manner and

following a rather strict schedule of feather replacement, which may

vary from species to species, even populations of a single species. Thesingle generation of feathers that is brought in by each moult is known

as a plumage.

Feathers may change in appearance as they are replaced as a functionof the bird’s age, gender, and seasonal changes. In birds of temperate

locales, feathers grown in the Fall (the Basic plumage) may differ mark-

edly from those grown in the Spring (the Alternate plumage) just before

the breeding season.The quantity and quality of nutrition and other factors affecting the

health of a bird can affect the appearance of growing feathers, especially

the flight feathers. Malnutrition, for example, may result in the presenceof a series of V-shaped grooves across the vane. These grooves are causedby the poor development of the barbules and are known as growth bars

(Pyle, 1997).

Feather Structure

The main parts of a body contour feather, which form the outer cover of

feathers, are the shaft, the plates or vanes on either side of it and, in most birds, an aftershaft on the undersurface (Fig. 2).

Figure 1. Pterylosis of a male Single Comb White Leghorn Chicken.From Lucas and Stettenheim, 1972.




The shaft (or quill) is the longitudinal axis, and it is composed of two

segments, the barb-less calamus and the rachis. The calamus (or barrel)

is the short, unpigmented tubular base, largely implanted into the featherfollicle. It is approximately circular in cross-section and often tapered

toward the end. The rachis is the long, essentially solid portion of the

shaft above the skin.On each side of the shaft is a set of closely knit, fine branches that are

known individually as barbs and collectively as a vane. Proximally (closest

to the body) each vane is fluffy, while distally (away from the body) it is

firm and flat. The shaft serves as the scaffold, while the vanes provide thesurface for an airfoil or for covering and insulating the body.

The aftershaft is a structure attached to the underside of a feather at

the base of the feather, including featherlike structures composed of anaxis with barbs on each side.

Vane

The vane provides the surface for an airfoil or for covering and insulatingthe body. It consists of barbs (Fig. 2).

The vane of contour feathers varies in texture from base to tip as a

function of the structure of the barbs (and function of the feather). The

proximal portion of the vanes has a soft, loose, fluffy texture designated asplumulaceous or downy. This portion, concealed by other feathers, gives a

feather its property of insulation. The remaining portion of the vanes hasfirm, compact, closely knit texture designated pennaceous. It is a thin sheet of barbs that covers the body, and gives the feather its airfoil. The propor-

tion of downy and pennaceous texture varies and is one of the criteria for

defining certain types of feathers. Remiges and rectrices have entirely pen-

naceous vanes, whereas semiplumes are entirely plumulaceous.Barbs do not attach to opposite sides of the shaft at exactly the same

level, yet the total number of barbs is very nearly equal in both vanes. The

bare primary branch of barbs is called the ramus, the term barb beingreserved for the ramus and its vanules, the barbules on one side of a barb.

Figure 2. Main parts of a typical contour feather, exemplified by a

feather from the middle of the dorsal tract of a Single Comb WhiteLeghorn Chicken. From Lucas and Stettenheim, 1972.




Figure 3 (above). Plumulaceous barbules of a Common Pigeon. From

Lucas and Stettenheim, 1972.

Figure 4 (right). Pennaceous barbules from the middle of a secondary remix of a Single Comb White Leghorn Chicken. Both have been turned

on their long axes so that they can be shown in side view. From Lucas

and Stettenheim, 1972.

Figure 5 (below). Segments of two pennaceous barbs from a contour

feather of a Single Comb White Leghorn Chicken, showing the inter-

locking mechanism. The barbs are seen obliquely from the distal endto show interlocking of parts. From Lucas and Stettenheim, 1972.




The ramus has the shape of a somewhat compressed filament that tapers

in height from base to tip. The branches of a barb are the barbules, also

known as radii.Plumulaceous barbules are characterized by a relatively short, strap-

like base and long, slender pennulum (Fig. 3). In spite of their simplicity,

plumulaceous barbules have distinctive characteristics in many orders orbirds, even lower taxonomic groups of birds, and are very useful to iden-

tify feathers.

Because plumulaceous barbules are less variable than those on the

pennaceous portion of a vane (particularly the barbules on the inner por-tion of the distal vanule of the basal barbs), they are very useful to identify

isolated feathers. Identification keys have been produced based strictly

on the characteristics of plumulaceous barbules [see Chandler (1916) andDay (1966)].

The dimensions of a feather (length, width, calamus length, downy

part, aftershaft length) as well as its curvature (including lateral cur-

vature) can assist identifying from which species of bird or tract they originated. A feather’s outer surface can always be told by the smooth side

of the shaft, which faces away from the body except in certain coverts on

the underside of the wings. One of the most distinctive features of a

feather is its coloration and patterning. Of course, this characteristic is of little utility when the feather is white or has been dyed.

Pennaceous barbules make up the flat, closely knit portions of the vanes. They are differentiated on both sides of a barb; even the ramusis asymmetrical (Fig. 4). The side of a ramus facing the distal end (tip)

of a feather is flatter than the side facing the proximal end (base),

and may even be concave (Fig. 5). Pennaceous barbs are held together by a

flexible, self-adjusting mechanism that is complex in details yet simple inessence. The distal barbules of one barb cross over the proximal barbules

of the next barb on the distal side. Hooklets of the former grasp the dor-

sal flanges of the latter, thereby interlocking them (Fig. 5). Dishevelled vanes with intact barbules can usually be straightened by running fingers

through the vane. One has to look no further for the origin of Velcro!

Feather Types

A single bird bears a wide variety of feathers, including (1) large, stiff

remiges and rectrices; (2) moderate-sized, partly-firm feathers that coverthe body (contour feathers); (3) small, fluffy down feathers; (4) hair-like

filoplumes; and (5) tiny bristles on the face.

Contour feathers

These are the main feathers on a bird’s body, which have already been de-

scribed above. Contour feathers are also known as pennae (singular: penna).

Remiges and rectrices

Remiges and rectrices are characterized by large size, stiffness, asym-

metry, vanes that are almost entirely pennaceous, and the absence of anaftershaft. Remiges and rectrices comprise most of the airfoil necessary for flying, often referred to as flight feathers.

Semiplumes

Semiplumes are sometimes combined with the downs, but they are

considered by Lucas and Stettenheim (1972) as a category between the

contour feathers and the downs, combining features of both rather

than any unique feature. Semiplumes have a long rachis (exceeding thelongest barbs) and have entirely plumulaceous vanes. Semiplumes are

distributed along the margins of tracts of contour feathers and in thetracts themselves.

Down feathers

There are two main categories of down feathers: natal down and definite

down. The natal down is present on a bird when it hatches or shortly afterward, while the definite down occurs in later generations of feath-

ers. Down feathers are wholly plumulaceous, the rachis being either

absent or relatively short. The texture of down feathers results primarily

from their slender flexible rami that bear long, segmented, filamentous

barbules without hooklets. Down feathers occur at various places on the




body, as a function of the need for insulation. The patterns of distribution

of definite down feathers vary between groups of birds.

Powder down

Feathers of many birds are dusted with a very fine substance that resem-

bles talcum powder. Small amounts of this powder are shed by ordinary plumules and contour feathers. However, the powder is chiefly produced

by special feathers, the powder downs which are commonly dispersed

over the body among the ordinary downs and contour feathers. The pow-

der is composed entirely of keratin. The powder down is derived fromcells on the surface and in the middle of each of the many ridges of barb-

forming tissue within a feather germ, not normally incorporated in the

barbs but lost.

Bristles

Bristles are characterized by stiff, tapered rachis and the absence of barbs

except at the proximal end. They are virtually all found on the head.

Filoplumes

Filoplumes are hair-like, consisting of a very fine shaft with a tuft of

short barbs or barbules at its tip. Filoplumes do not have a tapered rachisand have barbs only at the tip when fully grown. They are always situ-

ated beside other feathers, and may serve as an indirect yet very sensitivemeans for recording slight movements of the larger feathers nearby.

Coloration

Birds show an exquisite variety of colours and patterns of coloration,

including many bold and showy ones. The patterns are often species-specific and may vary within a species with gender, age and season.

All colours are produced by one of two physical processes: the absorp-

tion of specific wavelengths of light by natural pigments (pigmentation),or the interference of light reflected by biological nanostructures of con-

trasting refractive indices (structural colours) (Frank, 1939).

Pigments

Biochemicals deposited in feathers during their elaboration are varied

and include melanins, carotenoids, psittacofulvins, porphyrins, and afew unknown pigments (Frank, 1939; Völker, 1944; Brush, 1978b). Col-

oration may also be acquired by grown feathers from the environment,

like ferrous oxides present in mud or sand. Finally, a wide variety of natu-

ral or artificial dyes may be applied by humans to light-coloured feathers.The emphasis here will be on pigments in native feathers.

Pigments (also called biochromes) differ in their chemical make-up,

absorption properties (colours), mode of formation, mode of incor-poration and display in feathers, as well as in their response to various

physico-chemical treatments.

Melanins

Melanins are the most common and widely distributed class of pigments

in bird feathers, and almost the only one in mammals. Melanins also

occur widely among plants, animals, fungi, and bacteria.Melanins give the feather a black, reddish-brown, brown or yel-

low colour (Frank, 1939; Lubnow, 1963; Brush, 1978b). Generally the

colours produced by melanins lack saturation (i.e., are relatively dull)

because most wavelengths of visible light are absorbed, at least to someextent. Still, when combined with other pigments or structural modifica-

tions melanins can create bright, even stunning colours (see StructuralColours below).

Melanin is a heterogenous polymer synthesized through the oxida-tion of the amino acid tyrosine by a process that is in part autocatalytic

involving free radicals, but initially requiring the enzymatic activity of the

copper-containing oxidase tyrosinase. Tyrosinase catalyzes the conver-sion of the amino acid tyrosine to 3,4-dihydroxyphenylalanine (dopa),

then to dopaquinone, and so on (Brush, 1978b; Körner and Pawelek,

1982). Eumelanin is formed through subsequent intramolecular

rearrangements and polymerizations (Fig. 6). In the presence of sulfhy-

dryl compounds such as cysteine and glutathione there is production of




cysteinyldopas which oxidize, cyclize and polymerise to form another

type of melanin, phaeomelanin (Fig.6; Brush, 1978b). Most melanins are

insoluble and chemically intractable, though some are somewhat solublein alkali.

Melanin is synthesized in specific cytoplasmic organelles, known as

melanin granules, by specialized stellate pigment cells called melano-phores (melanocytes, when they lack organelle motility). Melanophores

do not develop in the growing feather per se, but rather lie at the base

of the growing feather (epithelial layer), actively producing and transfer-

ring melanin granules to the keratinocytes that will make up the featherproper. These pigment cells ultimately derive from neural crest cells that

form beside the neural tube early in development, which have migrated

to those parts of the body that are to be pigmented (Le Douarin, 1982).Melanin granules deposited on the surface of the keratinocytes enter the

deeper layers of the cytoplasm. With subsequent keratinization the pig-

ment granules become embedded in the horny substance of the epithelial

cells (Lucas and Stettenheim, 1972).The colours produced by melanins depend on the type of melanin

involved, and secondarily on the number of granules laid down. Four

types of melanins are known in birds:

(1) the eumelanins produce black or dark brown; eumelanin granulesare typically rod-shaped (0.5-1.2 µm).

(2) the phaeomelanins produce light brown, reddish-brown, or yel-low granules. Granules of phaeomelanin are spheroid or ovoidand smaller than those of eumelanin, the smallest granules giving

rise to rusty-brown to pale yellow colours (Lucas and Stettenheim,

1972). Phaeomelanins differ in solubility, as well as spectrally and

chemically, from eumelanins (Lubnow, 1963). Unlike eumelanins,phaeomelanins are soluble in alkali and can be extracted with cold

0.25 % NaOH solution (Lubnow, 1963).

(3) An iron pigment closely related to, or possibly identical to, tri-chosiderin—the iron pigment of human red hair—has also been

Figure 6. Presumed pathways of melanin biosynthesis. From Brush,

1978b.




isolated from red, brown and buff feathers of chickens, turkeys,

junglefowl and Bobwhites (Lucas and Stettenheim, 1972).

(4) Erythromelanins produce chestnut red, and have been hypoth-esized to occur in birds mainly on genetic grounds, but have never

been characterized adequately chemically.

Feathers, or parts of feathers, that contain melanin are usually moreresilient and less subject to wear than the unpigmented feathers or parts

of feathers (Burtt, 1986).

Carotenoids

Carotenoids are found in the feathers of birds from at least 10 orders (and

19 families) (Brush, 1981). Carotenoids produce most of the bright red,

orange and yellow hues of feathers, though not those seen in parrots, where psittacofulvins are involved instead (see below). When combined

with structural elements, especially blue, carotenoids also produce

shades of green.

Carotenoids are highly unsaturated hydrocarbons that are readily soluble in fats and organic solvents. For many years carotenoids were

labelled as lipochromes, a designation which no longer is desirable as

other groups of pigments (like the psittacofulvins) are also fat-soluble.

Birds, as all animals, cannot synthesize carotenoid pigments de novo and ultimately must obtain these pigments from their diet, directly or

indirectly from plants (Goodwin, 1984). However, many organisms, likebirds, can modify the ingested pigment to some extent (Goodwin, 1984).Both carotenes, made up of only carbon and hydrogen, and xantho-

phylls, which also contain oxygen, can be obtained in the diet, though

birds tend to absorb xanthophylls preferentially (one exception being the

flamingoes which absorb preferentially dietary carotenes) (Fox, 1976;Brush, 1981). Though carotenes turn up in feathers only rarely, they can

act as precursors of pigments that are deposited in feathers.

Several carotenoids have now been identified in the feathers of birds(Völker, 1944; Fox, 1976; Brush, 1981; Hudon, 1991). Feather colour usu-

ally correlates with the types of carotenoids deposited, particularly the

number of conjugated double bonds that they bear. It is not uncommon

for feathers to contain mixtures of several related carotenoids (Hudonand Brush, 1990; Hudon, 1991).

Feather carotenoids include:(1) dietary carotenoids: lutein, zeaxanthin, sometimes deposited

unaltered in feathers to produce orange-yellow to orange colours

(Fig. 7).

(2) red 4-oxo-carotenoids, produced through the enzymatic additionof one or two oxo (=O) functions at carbon 4 of the carotenoid

end-rings, extending the central chain of double bonds of dietary

carotenoids and shifting the colour toward red. Examples: astax-anthin, canthaxanthin, adonirubin, etc. (Fig.7).

(3) yellow carotene-3-ones produced through the migration of a

double bond on the carotenoid end-rings from position 5,6 to

4,5, shortening the chain of double bonds by one or two doublebonds yielding bright yellow pigments. Examples: canary xantho-

phylls (Fig.7; Goodwin, 1980; Hudon, 1991).

(4) light yellow picofulvins produced through hydrogenation of the

double bond 7,8 to produce 7,8-dihydro-carotenoids, in several woodpeckers (Stradi et al., 1998).

(5) an unusual, bright red, retrodehydro carotenoid, rhodoxanthin,presumed to be acquired directly from the diet, responsible forblue, violet and red feather colours in several fruit pigeons, and

dark red colours of cotingas (Völker, 1952, 1953).

During feather development the carotenoids are dissolved in lipoiddroplets. In the first stage of keratinisation the fat droplets disappear,

and the carotenoids are absorbed by the viscous keratin substance;

sometimes they are precipitated in the shape of fine particles which laterdissolve in the keratin (Desselberger, 1930).




The colorfastness of feather displays involving carotenoids varies

tremendously between taxa, from vanishing quickly after the death of

a bird, even in complete darkness [e.g., the pink or yellow blush, alsocalled flush, wash, tint, etc. of white feathers of several gulls, terns,

ducks, pelicans and ptarmigans (Stresemann, 1927; Höhn and Singer,

1980; Hudon and Brush, 1990)], to disappearing under filtered naturallight over a period of several months [e.g., the red feathers of Crested

Quetzal (Pharomachrus antisianus)], to being able to withstand display in

museum exhibits for extended periods of time, and retain their colour

almost indefinitely in darkness (e.g., Northern Cardinal, Cardinalis cardi-

nalis) (Völker, 1964).

Feathers containing carotenoids also differ markedly in the ease with

which they release their carotenoids to organic solvents, from being eas-ily washed away by organic solvents with little penetrating power, like

petroleum ethers, hexane, acetone (Hudon and Brush, 1990), to quickly

(in a few minutes) releasing them almost completely to a solution of

methanol at room temperature (Crested Quetzal), to even being resistant to organic solvents like methanol (most birds, including the Cardinal)

(Völker, 1964; Hudon and Brush, 1992).

Since the same carotenoids are involved in many of these examples,

the variation in colourfastness and binding strength must be related tothe strength and specificity of binding of the pigments to feather pro-

teins, and not to the nature of the carotenoids themselves (Völker, 1964):

it has been suggested that some blushes may be applied to the surface asa component of the preen gland secretion (Stegmann, 1954), while carot-

enoids in feathers may be bound more or less strongly and specifically to

feather proteins (Hudon, unpublished observation.).

Carotenoids in the Northern Cardinal (and the psittacofulvins of par-rots; see below) are bound to feather proteins of large size (> 200 kD)

different from feather keratins (Hudon, unpublished obs.). These pro-

teins alter the absorption properties of the pigments, shifting their peak of absorption to longer, less energetic wavelengths (which can be dem-

onstrated by heating the feathers in an oven), and dramatically extending

Figure 7. Examples of carotenoids found in the diet (top four) and feath-

ers of birds (all except β-carotene and β-cryptoxanthin).




the pigment’s stability and half-life, which would only be a few hours in

solution at room temperature (Hudon, unpublished obs.).

Traditionally, carotenoids in feathers have been extracted in strongbases like alkaline ethanol (e.g., 10% NaOH) over a steam bath, because

of the relative stability of most carotenoids in bases (though acido-

genic carotenoids, like astaxanthin, are often oxidized to respective acidderivatives in these conditions), but these methods lead to the complete

dissolution of the feather matrix. Extraction without feather destruction

is effected using acidified pyridine (Hudon and Brush, 1990), permitting

an examination of the remaining pigments (e.g., eumelanins), struc-tural colours and other morphological features. This method has proved

useful to remove pigments from fresh feathers (including those of par-

rots) to match badly faded ethnographic artifacts (Hudon, unpublishedobs.). Extraction with acidified pyridine also provides an easy and con-

venient means to determine whether carotenoids are involved (McGraw

et al., 2005).

Where carotenoid pigments are heavily concentrated, the ramus orrachis is frequently swollen, there is no differentiation into cortex and

pith, and the barbules are much reduced or altogether absent (Dessel-

berger, 1930).

Psittacofulvins

The bright red, orange, and yellow colours in the plumage of parrots are

produced by a class of pigment altogether different from carotenoids, which parrots also circulate in their blood, but seemingly do not use

for pigmentary purposes (McGraw and Nogare, 2004). Parrots instead

deposit psittacofulvins, until recently a structurally unelucidated fam-

ily of pigments (Völker, 1936, 1937; Hudon and Brush, 1992). Like thecarotenoids, the psittacofulvins are hydrophobic molecules. Unlike

carotenoids, however, they are synthesized endogenously by parrots and

do not appear first in lipoid droplets in growing feathers but are dis-solved directly in the keratinising cytoplasm of the cells (Völker, 1937;

Driesen, 1953).

Amerindians of the Amazon drainage and the Guianas apparently had

developed a means to reprogram the feather follicles of live parrots to

produce yellow or red feathers instead of the normal green ones by a pro-cess of “tapirage” which involved rubbing plucked areas of the skin with

a concoction containing the blood or skin toxin of Dendrobates tinctorius, a

member of the group of poison-arrow frogs (Métraux, 1944).Recently, the psittacofulvins found in the red feathers of the Scarlet

Macaw ( Ara macao) were chemically identified as consisting of four linear

polyenal structures:

tetradecahexenal, hexadecaheptenal, octadecaoctonal andeicosanonenal

CH3 - (CH + CH)n - CHO, where n varies from 6 to 9 (Stradi et al.,

2001).

Psittacofulvins can be extracted with acidified pyridine (Völker, 1936,

1937; Hudon and Brush, 1992). They change colour dramatically upon

initial exposure to this solvent, though the colour change is reversible if heating is not applied (Völker, 1937; Hudon, personal obs.).

It is not known how these pigments are synthesized by parrots.

Porphyrins

Unconjugated porphyrins are present in red and brown feathers of birds

from 13 orders, notably in the downy plumage and adult feathers of owls

and bustards (Völker, 1938; With, 1978). Porphyrins also occur in the hairof mammals.

Porphyrins characteristically produce an intense red fluorescence

under ultraviolet light.

Porphyrins are unstable and fade rapidly upon exposure to light, andthus tend to be restricted to those areas of the body protected from direct

sunlight (Völker, 1964; Lucas and Stettenheim, 1972).

Porphyrins are derived from the catabolism of the heme moiety of hemoglobin by the liver (which is another pigment used for the pigmen-

tation of the skin of birds, though not of their feathers) (Thiel, 1968).




Pigmentary porphyrins consist of four pyrrole rings united by methane

bridges into a super-ring. Feather porphyrins consist mainly in copro-

porphyrin III, but include also protoporphyrin IX and uroporphyrin I, which also appear in the eggshells of birds (Völker, 1938; With, 1978).

Members of the family of touracos (Musophagidae) deposit a unique

porphyrin, turacin, a copper-containing derivative of uroporphyrinIII, responsible for the rich red to purple-red colour of their remiges

and head feathers (Moreau, 1958; With, 1957). Turacin changes colour

(turns blue) upon exposure to rain, but reverses to its former colour

upon drying. Turacin is soluble in a weak alkaline solution and caneasily leach out of feathers. Considerable care should be taken when

washing these feathers to prevent leaching of the pigment. Yet turacin

is considerably more stable to light exposure than the free porphyrinsdiscussed above.

The green feathers of touracos and species from several orders of birds

[Blood Pheasant (Ithaginis cruentus), Roulroul (Rollulus roulroul), Jaçanas

( Jacana spp.), etc.] contain a porphyrin whose chemical relationship toturacin is not well understood, called turacoverdin (Dyck, 1992).

An unknown green pigment is found in the green feathers of eider

ducks (Somateria spp.) (Dyck, 1992; Hudon, unpublished obs.).

Adventitious coloration

Red and yellow colours in several species of waterfowl and some birds

of prey (e.g., the Bearded Vulture, Gypaetus barbatus) are the result of thedeposition of ferrous oxides picked up from the environment (mud,

sand) (Kennard, 1918; Höhn, 1955; Berthold, 1967). These colours are

relatively stable as they are an integral part of the plumage coloration.

The same could probably be said of pigments like ochre that are appliedby indigenous cultures.

Structural Colours

Structural colours in feathers are broadly classified as either iridescent

or non-iridescent, based on whether they change with the angle of view-

ing or illumination, or not. Until recently, these two classes of structural

colours were believed to arise from distinct physical processes, coherent

or incoherent scattering, respectively.In coherent scattering, colour production is described in terms of the

phase relationships among light waves scattered by multiple scatter-

ers, for example the interfaces afforded by rows of melanin granules ina keratinised matrix. Scattered waves that are out of phase destructively

interfere and cancel each other, whereas scattered waves that are in phase

constructively reinforce one another.

In incoherent scattering, in contrast, colour production arises as aresult of the differential scattering of wavelengths of light by the individ-

ual light-scattering elements, through Rayleigh scattering (erroneously

known as Tyndall scattering) or Mie scattering, with no relation to thephase relationships between the scattered waves.

It has become apparent in recent years that quasi-ordered arrays of

light-scattering elements in non-iridescent feathers also produce biologi-

cal structural colours through coherent scattering and interference (Dyck,1971, 1976; Prum et al., 1998, 1999; Osorio and Ham, 2002). The scatter-

ers are sufficiently spatially ordered at the nanoscale level to produce the

observed hues by coherent scattering but are not ordered enough at larger

spatial scales to be strongly or at all iridescent (Prum et al., 1998).

Iridescent colours

Iridescent colours are produced overwhelmingly in the barbules of feath-ers. Iridescent colours are always associated with melanin granules, the

granules being deposited in highly ordered layers parallel to the upper

surface of a barbule or one of its sections, keratin/melanin granule or

air-vacuoles in melanin granules affording interfaces of contrastingrefractive indices for reflection (Lucas and Stettenheim, 1972).

The colour of the iridescence will vary as a function of the thickness of

the granules, intervening keratin layers, and/or air-filled cavities, numberof layers and spacing of light-scattering interfaces, as well as with the

angle of viewing and light incidence on the feather (Dyck, 1976).




Figure 8. Coloured barbules in the pennaceous

part of a humeral feather from a Bronze Turkey.From Lucas and Stettenheim, 1972.




In some species, like the wild turkey, the pennula of iridescent bar-

bules become highly modified: broadened, flattened, and twisted so that

they lie in the plane of the vane (instead of perpendicular to it). As a result,

the vane presents a very smooth surface, not unlike a closed venetianblind (Fig. 8). Barbs in the iridescent zone contain such a large amount

of melanin that separate granules can no longer be made out (Lucas and

Stettenheim, 1972).In hummingbirds, the melanin granules instead contain gas-filled

air vacuoles in single or multiple layers, causing iridescence through

interference of light reflected from the upper and lower surfaces of the

vacuoles (Lucas and Stettenheim, 1972; Dyck, 1976).

Non-iridescent Colours

Non-iridescent colours (most blues and violets, many greens) are pro-duced by modified rami or shafts, except in blue fruit pigeons ( Alectroenas

spp.), crowned pigeons (Goura

spp.) and a few other taxa, where they are

produced in the barbules (Lucas and Stettenheim, 1972; Dyck, 1976).In these systems the reflections responsible for colour-production

occur at keratin-air interfaces, in the spongy structure of large, polygo-

nal medullary cells of the barbs and shafts (Fig. 9). Electron microscopic

studies show the spongy structure to be a complicated network of inter-connected keratin rods of fairly constant diameter separated by air-filled

channels (Dyck, 1971, 1976), where colour is determined by the diame-

ters of the rods, which vary from 200 to 400 nm. Melanin granules, whenpresent, function primarily to absorb the transmitted light, not reflect

light as in iridescent colours (Dyck, 1976).

In white feathers, there is no underlying pigment and the rods of

keratin are of a larger diameter and reflect all wavelengths of light about equally. In structurally coloured rami, the cortex is unpigmented and

generally thin, usually referred to as cuticle. Combined with the presence

of yellow carotenoids or psittacofulvins the cortical layer will appeargreen (Fig. 9).

Figure 9. Rami that are coloured entirely or

partly by interference in cloudy cells. These

cells are shown in blue because they arethe source of this colour in whole feathers,

although they do not actually appear blue in

cross-section, i.e., without a background of

melanin.A and B, Green Magpie (Cissa chinensis),

head

feathers;

C, Vulturine Guineafowl ( Acryllium vulturi-

num) outer vane of remix;

D, Red-rumped Paradise Tanager ( Tangara

chilensis), abdominal feathers;E, Gouldian Finch (Poephilia gouldiae), dor-

sal feather;F, Masked Tanager ( Tangara nigrocincta ),

head feather. From Lucas and Stetten-heim, 1972; redrawn after Frank, 1939.




Feather Fauna

The feathers of live birds provide cover and food for a wide variety of

organisms, besides the clothes moths that are the bane of museum col-lections.

Chewing feather lice (Mallophaga)

Chewing feather lice are small (mostly less than 5 mm long) wingless,flattened insects, armed with chewing mandibles that are ectoparasites of

birds, feeding on the feathers (or hair) of their host. Chewing lice spend

their entire life on their host. Transmission from one host to another usu-ally occurs when hosts come in contact, since lice are unable to survive

long off a host. Each species attacks one or a few related species of hosts,

and lives on a particular part of a host’s body. Eggs are laid on the host,

usually attached to hair and feathers. Chewing lice can be quite irritatingto their hosts. Heavily infested animals are often emaciated (Borror and

Delong, 1989).

Mites

Mites are very small. Their small bodies allow them to exploit habitats

too cramped and food sources too meager for insects, and their life his-

tories are often many times more rapid. Not all bird-associated mites areparasitic; some may even be beneficial.

At least 2500 species of mites from 40 families are closely associated with birds, occupying all conceivable habitats on the bodies and nests of

their hosts (Proctor and Owens, 2000).Even taxa that lack feather mites, such as penguins, are attacked by

ticks. Feathers provide a habitat for the greatest diversity of bird-associ-

ated mites, some of which live on feather surfaces (plumicoles), whileothers live inside the quills (syringicoles) (Proctor and Owens, 2000).

Unlike feather lice, which consume feathers, plumicolous mites con-

sume mainly uropygial-gland oil (predominantly waxes and fatty acids)

and scurf, pollen and fungi that adhere to the feather barbs. The mites’

mouthparts are designed for scraping not chewing.

Bacteria

A soil bacterium, Bacillus licheniformis, was described recently as capable

of degrading feathers in poultry waste (Williams et al., 1990), and foundto be present in the plumage of many North American birds (Burtt and

Ichida, 1999).

Burtt and Ichida (2004) hypothesized that Gloger’s rule of ecogeo-graphic variation, whereby populations living in climates with high

relative humidity tend to be darker than those living in climates with low

relative humidity, might find an explanation in the increased resistance

to bacterial degradation of feathers laden with melanin pigmentation(Burtt, 1986).

However, even when applied liberally to the plumage of live birds

housed outdoors, even in humid conditions, B. licheniformis does not appear to degrade feathers (Cristol et al., 2005), raising the question as

to whether this and other keratin-degrading microbes have any effect on

the feathers of live birds.

Effect of Light on the Colour of Integumentary

Derivatives

There have been surprisingly few studies of the effect of light on the epi-

dermal appendages of wild species of vertebrates, e.g., range of naturalpigments and packages (scales, feathers, fur) (Cato et al., 2001), and

there are no published data about fading rates and acceptable exposure

levels for different types of feathers (Solajic et al., 2002).Moreover, studies carried out so far, and some currently in progress

at the British Museum, have been concerned mainly with the feathers of

parrots (Horie, 1990; Solajic et al., 2002), which contain an unusual suite

of pigments, the psittacofulvins, and so cannot be generalized to othermore common pigment systems, though they might be some of the most

susceptible to fading (Solajic et al., 2002).

Unfortunately, the small size of feathers, complex patterning and dif-ficulty to acquire large amounts of material greatly impede a systematic

study of the effect of light on a wide range of feathers. By contrast, furs




are often readily available and often of large enough size to allow for a

study, with controls and replicates. Moreover, furs also come in a vari-

ety of colours, including colour morphs or variants, which might permit

evaluation of the effect of pigment composition on rates of fading. Withthat in mind I set out to compare the effect of light on the fur of three spe-

cies of carnivorous mammals (the marten, mink and otter); specifically Iset out to:

1) gather quantitative data on rates of fading of furs known to be

sensitive to light in museum displays;

2) compare fading in species of different colours and mane structures;3) evaluate the remedial effects of an antioxidant (butylated hydroxy-

toluene) on fading.

Methods

Tanned skins of Mink (Mustela vison), Marten (Martes americana) and River

Otter (Lutra canadensis) were acquired from Halford Hide & Leather Co.

Ltd, Edmonton and cut into many 6.2 cm-long strips spanning the areabetween the dorsal and ventral midlines (except for the otter strips which

ran along the dorsal midline).

Strips that differed noticeably in appearance were set aside. The

remaining (similar) strips were drawn randomly and subjected to differ-ent treatments or used as controls. Most experiments were represented

by at least two strips, except for the methanol control, and the otter sam-

ples, where there was only one sample for each treatment.One set of samples was treated with an antioxidant, butylated hydroxy-

toluene (Sigma Chemical Co.; 1% in methanol), for 50 or 100 hours; a

control strip was bathed in methanol for 100 hours.

The fur strips were stapled on individual Atlas Electric Devices Fade-ometer test masks (No. SL-8A-3T) with a 6 cm x 6 cm window, ensuring

that the samples from a single skin visually matched in appearance (the

hair always pointed in the same direction). AATCC Blue Wool Light-fastness Standards (L2 to L7) were also mounted and run concurrently

to monitor light exposure levels. All samples were exposed to light in

an Atlas Weather-O-meter, Model Ci35 equipped with a continuous

water-cooled xenon-arc lamp shielded by a Soda Lime outer filter and

borosilicate inner filter (Option E in AATCC Test Method 16-1993; AATCCTechnical Manual, 1998).

Colorimetric and spectral readings were taken of all samples (N = 26)after 0, 5, 10, 20, 40, 80, and 160 hours in the weatherometer. Colorimetric

determinations were made with a HunterLab ScanLab XE spectrocol-

orimeter (0°/45° geometry; 50 mm diameter aperture) connected to a

Dell Latitude C800 laptop (and driven by HunterLab Universal software v. 4.10). Each sample was read twice. An Ocean Optics USB2000 spectro-

photometer operated with OOIBase32 v. 2.0.1.4 was used to obtain visible

spectra of smaller areas of each sample (10.32 mm diameter) using a ISP-REF illuminated integrating sphere; sampling was done at the centre of

the plate, as well as at 15 mm above, below and to the left and right of the

centre. By the end of the experiment, 364 readings had been taken on the

colorimeter and more than 1092 spectra were acquired. Fading was esti-mated by determining ∆ECIELAB and ∆L* for CIELAB illuminant D65 and

10° observer data.

Results and Discussion

The three furs examined differed significantly in their reaction to expo-

sure to light in a fade-ometer. Both mink and otter fur darkened initially

(L* decreased) upon exposure to light, then slowly lightened. The martenfur, in contrast, lightened rather monotonously through that time inter-

val (Fig. 10). After 160 hours of light exposure in the fade-ometer, the

lightness of the mink fur, but not of the otter, had returned to near the

level when the experiment started. The otter fur gained only about half the lightness it had lost on initial exposure to light (Fig. 10).

The fur coloration also changed in a species-specific way, reddening

in the otter and mink, but initially becoming less red in the marten beforegetting redder as in the other species (Fig. 10).




Figure 10. Fading rate curves for tanned marten, mink and otter fur (one

example each; colour and lightness variables are CIELAB units; error

bars are ±SD). Exposed to light in an Atlas Weather-O-meter, Model Ci35

equipped with a continuous water-cooled xenon-arc lamp shielded by aSoda Lime outer filter and borosilicate inner filter (Option E in AATCC

Test Method 16-1993; AATCC Technical Manual 1998).

Figure 11. Fading rate curves for otter fur with and without 1% BHT,an antioxidant (and methanol wash control). AFU’s are AATCC Fading

Units or hours of exposure calibrated using AATCC blue wool standards

(AATCC Technical Manual 1998).




Unfortunately, the species differ in hair length, pigment arrangement,

concentration and presumably composition; so the source of the species-

specificity of reaction to light cannot be completely ascertained.

In another experiment we tested whether scavenging free radicals,generated either directly from exposure to light, or indirectly from pho-

tochemical processes set afoot by light irradiation (Feller, 1994), usingan antioxidant (1% butylated hydroxytoluene), might impede or slow

down the photo-oxidation of pigments, particularly since melanins can

sometimes act as free radical traps (Geremia et al., 1984). Surprisingly,

however, addition of an anti-oxidant did not affect the direction nor therate of change of coloration, for example in the otter skin (Fig. 11).

In conclusion, conservators need to be aware that integumentary

colour systems, even those with only a single pigmentary or structuralsystem, may vary markedly in sensitivity and response to exposure to light

from one species to another. Future efforts should attempt to document

the effects of light on a wide variety of sources of colours and types of

feathers and to carry out controlled fading experiments on a wide variety of organic materials (feather, fur, scales, etc.).

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AuthorJocelyn Hudon PhD

Curator of Ornithology Provincial Museum of Alberta

12845 – 102 Avenue

Edmonton, Alberta T5N 0M6

Tel: (780) 453-9179Fax: (780) 454-6629

[email protected]

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