Ornithology Specimen Preparation

Statement of Purpose

These links and documents contain information about ornithology specimen preparation.

Contributors

Emily Braker

Introduction

Bird specimens are prepared in multiple formats depending on anticipated collection needs and utility.

Study skins are the standard method of preparation in Ornithology Collections, though skeletons, fluid-preparations, and spread wings are also commonplace. Non-skin preparations represent a growing proportion of collections as emerging museum technologies facilitate discovery (e.g., CT scanning, 3D photogrammetry, high resolution focus stacking). Additionally, tissues and symbionts are often collected at the time of preparation.

Study Skin Preparation

Study skins capture the outward appearance of an individual, preserving anatomical structures and plumage. Bird skins are prepared in a standard pose in order to provide a basic unit of comparison as well as to minimize storage footprint. Large, long-billed, or crested taxa may have slight variations on the classic cylindrical study skin shape, such as folded necks and legs, or heads turned to the side to consolidate fragile extremities or highlight diagnostic morphology.

Historically, study skin preparation follows Chapin (1923) and Hall (1962), with slight variations in method unique to individual preparators. Liberal application of chemical pesticides such as arsenic or mercuric chloride on the inside of skins to deter protein-feeding pests has largely been eradicated due to human health and specimen conservation risks, and improvements in collections storage systems. Generally, no chemicals are employed in the preparation process save for occasional use of a mild detergent to remove oils or blood from the skin as needed. Often a non-chemical absorbent is used in lieu of washing, such as corncob dust, cornmeal, or sawdust. However, preparators in tropical field conditions may opt for a desiccant such as Borax to discourage rot, though the long-term consequences of Borax on preserved study skins are unknown.

Skin preparation follows these general steps (see Preparation Procedure Resources below for links to detailed study skin preparation guides):

1. Data gathering – measurements, weight and various external attributes (e.g., molt, colors, cloacal protuberance, brood patch) are recorded prior to skinning. Specimens may also be examined for ectoparasites at this stage.
2. Skinning - An incision is made and the skin is worked away from the carcass, cutting at the knees, tail, humeri and posterior skull to extract the body core and retain the extremities with the skin. Internal data attributes are documented as they are encountered, such as fat deposition, body molt, bursa, skull ossification, gonad measurements and ova development.
3. Tissue collection – Tissues are typically taken at this stage. Detected internal symbionts may be harvested if desired.
4. Cleaning – The skin is cleaned of residual tissue, organs, blood, fat and oils. Especially fatty birds may require use of a scraping tool or fleshing wheel in addition to standard dissection instruments to fully strip grease from the skin. Washing or use of an absorbent are typically employed at this stage. Wet skins are dried with forced cold air or tumbled in absorbent.
5. Stuffing – The wings are tied in place internally and balled cotton is inserted into each eye orbit. The skin is stuffed with cotton or polyester batting by wrapping a dowel rod or shaped manikin. The bill and legs are tied for added stability.
6. Drying – Feathers are smoothed and the skin is either wrapped or pinned in position on a board to dry.

Skeleton Preparation

Bird skeleton preparation generally follows the study skin methods outlined above, though no bones are cut during processing to preserve the integrity of the resulting osteological specimen. Bones are cleaned using Dermestid hide beetles, maceration, or burial. Other methods such as boiling are not an accepted museum technique.

Following defleshing, bones may be treated with ammonia, detergents, enzymes, hydrogen peroxide, or ethanol to degrease, bleach, or surface clean elements. Some institutions discourage application of chemicals due to the unknown long-term conservation effects on specimens. However, solvents are widely used on greasy specimens and often considered necessary to draw out fatty marrow that can lead to data dissociation through leaching onto data tags or by making bones difficult to number.

See Preparation Procedure Resource section and Skeleton Preparation page for step-by-step skeleton preparation procedures.

Fluid-specimen Preparation

Pickling preserves the whole organism and allows for future examination of internal structures. Bird specimens are fixed in 10% buffered formalin before preservation in 70% ethanol. Bird fluid specimen preparation follows these general steps:

1. Data gathering - (see above)
2. Tissue collection – Fixation disrupts protein chain structure and renders tissues unsuitable for DNA extraction, therefore tissues must be collected prior to fixation.
3. Fixation - Carcasses are injected with 10% buffered formalin minimally in the thoracic, abdominal and cranial regions, as well as in major muscle groups for large taxa to ensure adequate fixative penetration of dense internal structures. Specimens are then placed in a formalin bath. Fixation time is dependent on specimen size and must allow for complete arrest of post-mortem changes in tissues yet avoid decalcification of the skeleton through prolonged soaking. Specimens should be removed from the bath once firm to the touch and no longer soft-bodied.
4. Ethanol laddering – Fixed specimens are rinsed and transitioned to ethanol in gradually increasing concentrations. Stepping up ethanol using the ladder method prevents osmotic shock as the specimens are transitioned from a water-based fixative to a comparatively dehydrated ethanol solution.

Buffered Formalin Recipe (per 1 liter of solution):

• 9 parts distilled or deionized water
• 1 part 37% formaldehyde
• 4g monobasic sodium phosphate (NaH₂PO₄H₂O)
• 6.5g dibasic sodium phosphate anhydrate (Na₃HPO₄)

Spread Wing Preparation

Spread wings are a relatively recent preparation method that involves creating an extended dried wing specimen, usually accompanied by a corresponding partial skeleton or partial skin. Spread wings have applications in studies of wing topography, molt, flight behavior and dispersal ability, and allow users to view the primary feathers, which are folded and obscured during study skin preparation. Spread wing preparation procedures follow these general steps:

1. Data gathering - (as above)
2. Wing removal – a standard wing side is selected by the preparing institution to promote uniform units of comparison and facilitate ease of storage (e.g., nested left wings). The wing is cut at the humerus and removed, leaving scapular feathers to remain with the study skin.
3. Cleaning – an incision is made beneath the marginal coverts along the ulna, and the seven surrounding forelimb muscles are removed. The incision is sewn closed.
4. Drying – The wing is fully extended and pinned into position to dry.

Preparation Procedure Resources

Chapin, J.P. 1923. The preparation of birds for study. American Museum of Natural History, New York. N.Y. Available at http://digitallibrary.amnh.org/handle/2246/7193

Drovetski, Sergei. 2007. Preparation of Avian Specimens for Research Collections.

Hall, Raymond. 1962. Collecting and preparing study skins of vertebrates. Museum of Natural History, the University of Kansas, Lawrence. Available at http://museum2.utep.edu/mammalogy/vertebratespecimens.pdf

Proctor, N. and P. Lynch. 1993. Chapter 11: Preparing Study Skins, Manual of Ornithology Yale University Press, Hartford.

Slater Museum of Natural History. 2005. Bird Skinning. https://www.pugetsound.edu/files/resources/2355_BirdSkinning.pdf

Szabo, Ildiko, Preparing Bird Specimens. Beatty Biodiversity Museum website (multiple resources provided): https://beatymuseum.ubc.ca/research-2/collections/cowan-tetrapod-collection/working-with-birds/

Winker, Kevin. 2000. Obtaining, Preserving, and preparing bird specimens, Journal of Field Ornithology, 71(2), 250-297. https://doi.org/10.1648/0273-8570-71.2.250