Snarge Busters

  • Published
  • Smithsonian Institution
For more than four decades, military and civil aviation safety personnel have been sending bird remains recovered from bird aircraft collisions (bird strikes) to the Smithsonian Institution's National Museum of Natural History for identification. In the early years, whole feathers, partial carcasses, and a variety of bird parts were sent to the museum for species identification.  Whole feathers and feather fragments are washed to regain their natural shape, color, and texture, and then they're compared to the museum's vast research collection of some 620,000 specimens for an exact species match.

As time passed, the bird evidence became more and more, minute-small bits of fluffy feather down wiped on a paper towel or saved in a barf bag found its way to the Feather Lab.  More recently, airfield personnel and safety offices have become expert detectives and are so good at finding bird strike evidence that sometimes only blood and/or tissue (otherwise known as 'snarge') is available after birds and aircraft collide.

Now, the Lab's team of three-Carla Dove, Marcy Heacker, and Nancy Rotzel; otherwise known as the 'Snarge Busters'-are combining new technologies with old skills to positively identify species of birds involved in birdstrikes.  In 2003, the Feather Identification Lab at the Smithsonian Institution joined forces with the Federal Aviation Administration and the US Air Force (USAF) to add a new 'tool' to the arsenal of techniques used to positively identify bird strikes that only contain minute blood and tissue evidence.  That new tool is....... DNA.  Bird strikes have cost the USAF about $35 million annually since 1985. What kinds of birds cause this kind of damage? The only way to be sure is to send in the evidence and have the species positively identified using the gamut of tools now available.

Although the usual suspects are larger birds such as gulls, waterfowl, and hawks, you might be surprised to know that a bird as small as a golden-crowned kinglet (6.2 g) caused more than $74,000 damage to a B-2 bomber. On average, small perchingbirds cost the USAF $1,000/strike, so YES, every bird identification is important. The number of bird strikes reported by the USAF continues to rise and now tops 5,000 strikes annually. While other wildlife such as deer, wild dogs, coyotes, and bats present hazards to aircraft, birds comprise about 98 percent of all wildlife strikes.  Several factors contribute to the rise in bird strike reporting: increased awareness of bird strikes through dedicated wildlife hazard mitigation specialists, increased aircraft operations, and increased population of birds. Other factors, such as the ease of on-line birdstrike reporting, educational training, and accurate, timely species identifications undoubtedly also contribute to higher reporting rates.

About 50% of the cases received in the Feather Identification Lab are still identified quickly and accurately, using the whole feathers recovered from the strike in comparison with the museums' collection of bird specimens. If, however, the sample contains 'snarge,' it now goes directly to the DNA lab for processing and possible identification.  DNA Identification Process. We selected the 'barcoding gene,' a small fragment of a mitochondrial gene known as cytochrome oxidase 1 (CO1) as our target DNA marker for our birdstrike identification database. Sequencing the CO1 gene (a 650-base pair region of mitochondrial DNA) for all of life on earth is now part of a global initiative called the Barcode of Life Database (BoLD), with a goal of having all 10,000 species of birds completed by 2010. BoLD now contains sequences for 94% of the bird species of the US and Canada.

To process an unknown sample, first, the 'snarge' is sampled, the DNA is extracted, and a million copies of the barcode gene are amplified. Then the DNA is labeled with fluorescent tags, which are analyzed by a DNA sequencing machine. The unknown DNA sequence is finally compared to the on-line BoLD for species identification.

During Fall 2006, the Feather Identification Lab tested this DNA database by submitting over 800 samples that contained only tissue, blood, or non-diagnosable feather fragments for identification using DNA barcoding. The DNA analysis provided positive species identification in over 68% of those cases. The identified cases for this short period of time comprised of 128 species representing 14 orders of birds.

Although DNA technology is considered a major breakthrough for birdstrike identifications, we still rely on microscopic methods in about 32% of the cases, because not all of the cases submitted for DNA analysis contain viable DNA.

The types of material that most often failed at DNA extraction included samples that contained mold or were received on paper towels. Mold growth takes over the tissue sample, making it difficult to find material for DNA analysis. Paper towels provide no preservation to the sample, and the DNA rapidly degrades, unless the sample is sprayed with 70% ethanol.

DNA analysis increases the number of submitted samples that can be positively identified, thereby enhancing the amount of available accurate data. Precisely identifying what wildlife our aircraft strike and properly reporting where and when the strike occurs, enables others to specifically research, develop, and enhance programs which will effectively and efficiently target and mitigate the "culprits."