Micromorphology of Feathers using the Scanning Electron Microscope

ANNE DAVIES

The Metropolitan Police Forensic Science Laboratory, 2 Richbell Place, Holborn, London W.C.I, England

T h i s paper i s a n account of the work done as a result of a case of bird larceny being brought to the Metropolitan Police Forensic Science Laboratory. T w o m e n had been accused of stealing twelve chickens. They denied this and said any feathers on their clothing were duck feathers. A few feather fragments were found. I n - vestigation of these using the scanning electron microscope revealed that they were not from duck feathers, but from the feathers of a member of the sub-order Galli to which the domestic chicken belongs.

(Note : a glossary of terms used appears at the end of the article)

Occasionally cases arise which involve the identification of feathers. When the feathers are large and distinctive this is a relatively easy task. However, when they are small, indistinguished or fragmentary, their identification poses a much greater problem. One such case was recently received in the laboratory.

Two men were accused of stealing a number of chickens, and a search of their clothing revealed a few downy feather fragments. The two men denied stealing the chickens and maintained that the feathers found on their clothing were ducks' feathers.

According to Chandler (1916) it is possible to determine to which group a bird belongs by the structure of its down. (The use of the loose term 'group' is necessary as sometimes one can determine a bird's family by its down structure and sometimes only its order). As the ducgs are in a different order from the domestic chicken, it seemed that further investigation of the feather fragments might prove fruitful.

For the initial microscopic study of the feather fragments, both the compound optical microscope (with and without phase contrast facility) and the scanning electron microscope were used. After examining the first few scanning electron micrographs, it was obvious that much more information could be obtained in greater detail using the latter instrument due to its superior depth of focus, resolution and magnifying power. Consequently, the study was completed using the scanning electron microscope.

Preparation of the feather fragments for examination in the instrument was relatively easy. The relevant parts were attached to specimen stubs, by means of two-sided sellotape. They were coated with gold/palladium or carbonlsilver (either seemed equally effective) to provide a conducting surface. They were then placed in the microscope for examination. As cameras are a standard fixture of the scanning electron microscope, it was easy to keep a photographic record.

Figure 1. Diagram of a. Typical Contour Feather.

b a r pennulurn 1-r

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villi

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Figure 2. Diagrammatic Downy Barbulc.

base of shaft

a t t o c m

Figure 3. Diagram of Basal Downy Barbs.

Figure 4. Meleagris virginiana (Turkey) Downy Barbules with Rings (X 160).

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Figure 5. Gallus domesticus (Chicken) Ring Node (X 5,100).

Figure 6. Phasianus colchicus (Pheasant) Ring Node (X 1,750).

Figure 7 . Phasianus colchicus Slipped Ring ( X 825).

Figure 8. Gallus domesticus Two Slipped Rings Adjacent to a Third (X 2,100).

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Figure 9. Gallus domesticus Pronged Node ( X 5,100).

Figure 10. Anser anser (Goose) Expanded Node (X 4,200).

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Figure 11. Anas platyrhynchos (Duck) Expanded Nodes and Prongs (X 840).

Figure 12. Barb from Suspect (X 100).

Figure 13. Barbules from Suspect (X 170). Note three ring structures.

Figure 14. Enlargcd detail from Figure 13 of the three ring structures.

Discussion of the Microstructure of Chicken and Duck Down

The domestic chicken (Gallus domesticus) is a member of the sub-order Galli. The members of this sub-order are commonly known as the game birds. Ex- amples are turkeys, pheasant, peacocks, quails, partridges, ptarmigan grouse.

Down shows varying degrees of specialisation of structure depending on where on the bird it occurs. This difference in structure is particularly pro- nounced in the gallinaceous birds. The down structure typical of this group is to be found on the down barbs of the unspecialised contour feathers. I t occurs on the proximal barbules of the distal vanules of these barbs.

The characteristic down barbules are relatively long, averaging 3mm in length. They are densely set on the barb. Their most proximal nodes are poorly developed, but distally the nodes have distinctive ring structures (Figures 4 - 4 ) . These rings often break loose from the nodes and slide along the barbule, forming clusters. (Figures 7 and 8) These ring structures have not been found on the down of birds other than the Galli and therefore they can be regarded as usefully diagnostic.

The structure of the down elsewhere on the contour feathers, on the plumules, aftershafts and at the bases of the remiges and retrices is less specialised, the barbules having prongs at the nodes rather than rings. (Figure 9) These pronged nodes are not easily distinguishable from the pronged nodes to be found on the down barbules of other birds.

The ducks belong to the family Anatidae (waterfowl). The down of this family is also highly specialised. Unlike that of the Galli, it is of almost uniform appearance wherever it occurs, only becoming reduced at the tips of the barbs. The barbules are short, usually being well under lmm in length. They are simple and threadlike for the greater part of their length, but towards the tip of each barbule there are several expanded nodes (Figure 10). At the distal end of the barbs these enlarged nodes are replaced by a few pairs of terminal prongs (Figure 11).

Results of the Investigation The preliminary examination of the downy barbules from the suspects'

clothing showed that the barbules near the base of the barb were densely set and most were over 3mm in length. By using the scanning electron microscope the typical gallinaceous ring nodes were revealed (Figures 12-14). The frag- ments were, therefore, from the plumage of a gallinaceous bird and were definitely not from that of a duck.

Conclusions This case is an example of how using Chandler as a basic reference and the

scanning electron microscope, a more detailed approach may be made to the identification of feathers. This work could be taken much further. For instance, Messinger (1965) stated that by studying in detail both the downy and pennaceous structures of a suitably large feather fragment it is possible to determine the species of bird from which it came. Messinger encountered difficulties with the magnification and resolving power of the compound optical microscope. These could easily have been overcome by using the scanning electron microscope which would, therefore, seem to be the ideal instrument for continuing research into the microstructure of feathers and its taxonomic significance. This research would benefit forensic scientists if it enabled them to identify feather fragments from at least the commercially important birds.

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Acknowledgements

Mr. G. Gowles, of the Bird Section, British Museum (Natural History), for his advice and photomicrographs. Unilever Research Laboratory, Isleworth, Middlesex, for the use of their Stereoscan Electron Microscope. Mr. P. Martin, of the Metropolitan Police Forensic Science Laboratory, for his drawings.

References

CHANDLER, A. C., 1916, A study of the structure of feathers with reference to their taxonomic significance. University of California Publications in Zoology,

13, 243. MESSINGER, G., 1965, Methods of identification of feather remains from Wetherall

Mes. American Antiquity 31 (Pt. 2, No. 2).

Glossary of Terms Used

Contour Feathers-The feathers which form the contour of a bird's body, always having well developed shafts.

Down or Downy Structure-That type of feather structure which is produced by elongated filamentous barbules ; as opposed to a :-

Pennaceous Structure-which is produced by differentiated distal and proximal barbules or modifications of them.

Plumules-Small down feathers more or less concealed and with the shaft never highly developed.

Shaft-The portion of the quill on which are borne the vanes. Vanes-That portion of the feather borne on one side of the shaft composed of

barbs, usually with barbules. Blade-The shaft with both its vanes. Ramus-A primary branch of the shaft. Barb-A primary branch of the shaft plus its barbules. Barbule-A primary branch of the ramus. Aftershaft-The ventral counterpart of the shaft, sometimes vestigial or absent. Remiges-Specialised contour feathers of the wing. Retrices-Specialised contour feathers of the tail. Vanule-All the barbules of either the distal or proximal series-bearing the

same relation to the barb that the vane bears to the feather plate. Nodes-The junctions of the cells of the pennulum of down barbules, usually

characterised by growths and swellings of some sort. Prongs-Short spiny outgrowths at the nodes of the down of many birds.