Contributed by Marcy Heacker and Carla J. Dove, PhD
Feather analysis can be utilized to identify the avian group or bird species in a variety of investigations and circumstances. Historically, morphological feather identification techniques were developed and utilized at the Smithsonian Institution, National Museum of Natural History for the determination of bird species involved in bird/aircraft collisions (“bird strikes”). In addition, feather identification techniques have been successfully used in the identification of bird species in feathered anthropological artifacts, prey remains, food contaminants and law enforcement cases.
While molecular analysis of bird remains and feather material has become an important part of the identification process – the traditional morphological analyses are still vital to the identification process. Depending on the material available, morphological feather analysis can be approached two different ways – whole/intact feather examination (feathers or feather fragments with color/pattern) and microscopic feather examination.
For most cases with intact/whole feathers or significant feather material, the evidence can be directly compared to a vouchered bird specimen (usually in a museum or university collection). Whole feather characters, such as feather size, color and pattern, are found in the pennaceous feather region – the distal part of a feather typically seen on a bird. These macro-characters can frequently be matched to known bird feather reference. It is important to consider where on the bird and what part of the feather the unknown material is from. Photographic comparisons of the unknown sample with vouchered bird specimens are helpful in case documentation. Also, consulting an ornithologist to assist in interpreting feather material and possible species plumage variation is important in all feather identification cases. Many times, identifications using whole feather material can be made to species level; however, matches with an individual bird may not be possible.
Microscopic feather analysis of the plumulaceous (downy) region of a feather can be diagnostic to the “group” (usually taxonomic order) of bird. Despite this limit, microscopic feather examination can be very helpful in the identification process. Microscopic feather characters can help focus and corroborate examination of whole feather material – and many times is the only technique available for minute or fragmented feather material. Standard comparison light microscopy (100-400x magnification) is the best way to examine plumulaceous feather material by comparing the unknown to referenced vouchered microslides. Scanning electron microscopy (SEM) can be used for analysis, but internal pigment patterns are an important micro-character that SEM cannot provide.
As with many trace evidence materials, the examiner needs to understand the variation that is possible with feathers – particularly in the microscopic plumulaceous feather characters. These characters are transitional in nature. Generally, character expression gradually changes along the feather barbules and barbs, along an individual feather and on the location of the bird’s body.
If nDNA analysis is successful, the profile can be compared to a known nDNA sample from a suspect or victim and provide a near certain association to a single person (with the exception of identical twins). Additionally, if no suspects have been developed, the profile can be searched in the Combined DNA Indexing System (CODIS) in an effort to identify the individual that the hair originated from. With regards to the limitations of nDNA, it can only provide identity of the individual the hair came from, but cannot provide information regarding the circumstances of the crime (e.g. if it is a head or pubic hair, if it has naturally fallen out or been forcefully removed, if the root is decomposed indicating it came from a deceased individual). Additionally, the overwhelming majority of hairs found in forensic casework do not possess enough tissue to conduct nDNA analysis.
While feather evidence is uncommon, the application of macro and micro feather analysis can be useful in interpreting avian material and is a tool for the forensic examiner.
The combination of microscopical hair comparison and nDNA or mtDNA analysis provides the criminal justice system with significantly more probative information than any of these techniques do alone. Microscopical comparisons and DNA analysis should always be considered in any case where hair evidence is important.
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5. Slater Museum of Natural History. 2005. Wing and Tail Image Collection. The University of Puget Sound. 20 May 2015.
6. U.S. Fish and Wildlife Service Forensics Laboratory. 2010. The Feather Atlas: Flight Feathers of North American Birds. 20 May 2015.