Pepper Trail is the first to admit he has an unusual skill set. Give him a single feather or a small fragment of a claw or a cooked hunk of breast meat, and he'll tell you the species of bird from which it came. As the world's leading criminal forensic ornithologist, Trail is asked day in and day out to perform these exact tasks. Over the past 18 years he has assisted with hundreds of investigations, testified in federal court 15 times, and handled more bird carcasses than anyone should. "All birders have life lists," Trail says. "I have a death list."

Trail isn't joking. He opens a file on his computer and scrolls through a list of 750 species of dead birds he has identified throughout his career. The decor of his work space at the National Fish and Wildlife Forensics Laboratory in Ashland, Oregon, blends bird-nerd kitsch with macabre relics of closed cases. A "Waddling Penguin Pooper" wind-up toy sits on a bookshelf still in its original packaging. Atop a filing cabinet is a confiscated necklace made from the claws and skull of a cassowary. Nearby is a long, sleek feather ripped from an Andean condor wing and attached to a pin that customs agents seized from a polka dancer coming into Chicago. "There's actually a trade in condor feathers from Peru to Germany to decorate polka hats," Trail says.

If a Fish and Wildlife agent ends up working a case that involves any sort of bird part, there's a good chance the evidence will land on Trail's desk for inspection. Because not all birds are protected equally, his IDs play an important role in the legal process that helps agents and prosecutors determine what laws are being broken and what charges can be brought against the perpetrators. It should come as no surprise that ornithological forensics is an exceedingly obscure career path. The field didn't even exist until the 1960s. Yet the size and scope of Trail's caseload — more than 100 cases a year, involving well over 1,000 pieces of evidence — attests to the fact that this little-known arm of law enforcement plays a critical role in conservation.

Sometimes Trail receives a blob of black sludge from an oil pit containing a decomposed bird and has to extract the feathers, restore them, and ID the species. Other times he gets the smashed remains of an animal demolished by a wind turbine. He has investigated high-end artifacts smuggled into the country — an indigenous Amazonian crown made from curassow body feathers, toucan throat feathers, and scarlet macaw tail feathers, for example — and cheap dream catchers peddled at tourist traps across the Southwest. The findings go both ways; the evidence in question might be made from perfectly legal turkey feathers or the feathers of a protected sub-adult golden eagle.

In 2013 Trail received a shipment of 43 hummingbirds. The carcasses, which were each about the size of an index finger, had been dried out and stuffed into red paper tubes that were decorated with matching satin tassels. Accompanying each was a Spanish-language prayer meant to invoke the mystical powers of la chuparosa, a colloquial Mexican name for the hummingbird, in order to help a man find his true love. That the animals were intact — no birdshot wounds, no decapitations, and with minimal damage to the colorful plumage — led Trail to suspect that they had been gently squeezed to death one by one in a human hand.

Trail didn't know what to make of them. "When they first appeared, it was like, 'Holy crap, what in the world is this?'" he says. A special agent had obtained the birds during an undercover buy from a man who was smuggling them in from Mexico. Following protocol, Trail unwrapped the birds from their ceremonial garb, identified the different species, and filed the necessary paperwork. A year later, another shipment arrived. And then another. The victims spanned at least 10 species, including violet-crowned, magnificent, and blue-throated hummingbirds — dazzling border species that attract birders to southern Arizona each year.

As familiar as Trail is with death, these hummingbirds pack an emotional punch. "Their very tininess makes them delightful and charming. Their extraordinary flying ability makes them impressive and awe-inspiring," he says. "Our power compared to their power is so great that it seems particularly perverse and cruel to kill them."

At age 63 Trail has identified enough dead birds for a lifetime, and he is looking at the prospect of retirement with greater fondness. More uplifting pursuits surely await the gentle soul who in his downtime pens award-winning poetry and dresses up as Charles Darwin to deliver scientific lectures.

But at the moment, Trail's retirement would spell disaster for the only wildlife-forensics lab in the world. "Pepper is one of a kind," says Ken Goddard, director of the lab. "If something happens to Pepper, we're SOL."

Pepper Trail didn't set out to make a name for himself in the dark world of avian-associated crimes. He was born in Virginia — his great-grandfather was Paris Pepper Trail, and his great-uncle was Peach Trail — but grew up in the Finger Lakes region of New York. A boyhood spent exploring the outdoors and admiring wildlife led to a degree in biology and a Ph.D. in ornithology from nearby Cornell University.

As a young ornithologist Trail plodded through South American rain forests in pursuit of the Guianan cock-of-the-rock. Then he strung together a few postdocs, which eventually landed him and his family in American Samoa. Island life was a formative experience, but with two young sons, priorities shifted, and Trail and his pediatrician wife moved to Ashland, a crunchy college town in southern Oregon world-famous for its Shakespeare festival. "The old Samoa-to-Ashland routine," Trail jokes of the transition.

The job market has never been friendly to ornithologists, so Trail split time during those first years back in the States picking up contract work, raising his sons, and writing a sci-fi eco-thriller for young adults. Out of the blue one day in 1998 he received a call from the National Fish and Wildlife Forensics Laboratory, which happened to be a short drive from his home. The lab's first and only ornithologist had left suddenly and cases were piling up — they needed a stopgap and wanted to know if Trail was available for a few months.

What started out as a temporary gig has blossomed into a nearly two-decade-long career. The forensics lab where Trail spends his days is an impressive facility equipped to analyze whatever evidence Fish and Wildlife special agents can uncover, whether it be illegal timber or a purported aphrodisiac made from bear gallbladders. There is a ballistics expert on staff, as well as genetics and pathology departments, an entire biosafety level-3 lab, and DNA-sequencing technology that seems fit for an episode of CSI.

Trail's tactics, however, are decidedly more analog. He's a morphologist who makes identifications by carefully studying and comparing anatomical characteristics of different bird parts. In most cases, this approach is not only faster and cheaper than booting up the sequencers and calling the genetics team, it's also equally effective. It has to be. Much like forensic evidence in a murder trial, the science behind Trail's work needs to withstand the scrutiny of aggressive defense attorneys, diligent judges, and impartial juries.

While from the outside the job can look like it's all gloom and doom, the analytical rigor it demands nourishes and inspires Trail's inner scientist. Patterns in his caseload have proven to be good fodder for research pursuits. For instance, after identifying thousands of birds that had died in oil pits — pools of runoff and waste that are found at oil-production sites — Trail collected the data, crunched the numbers, and published the most comprehensive scientific review of the issue, estimating that upward of 1 million birds perish in these pits each year, the vast majority of which are protected species. Moreover, Trail has devised and documented a method for determining an eagle species based solely on the curvature of detached talon fragments. "He is a scientist in the fullest sense of the word," says Ed Espinoza, deputy director of the forensics lab.

In the chain of command of wildlife law enforcement, Trail occupies a unique space. He doesn't chase down the bad guys or trek around collecting clues. Instead he enters the fray in the middle of an investigation, identifies the evidence, and then moves on to the next case. Oftentimes he is intentionally kept in the dark with regard to the investigation's details so that the circumstances of the alleged crime can't influence his scientific judgment. Rarely does he have the bandwidth to follow a case long enough to learn whether or to what extent the perpetrators are prosecuted.

Every once in a while, though, a case will be so perplexing or so unsettling that Trail can't help but lose himself in it. Take the chuparosas, for example. The most recent shipment of the hummingbird charms, which remains under active investigation, arrived at his office in February 2015. Because hummingbirds are protected by the Migratory Bird Treaty Act, Trail has been working closely with special agent James Markley in hopes of digging up everything they can on the trade to understand its size and impact. "It's pretty much unknown among U.S. ornithologists that this trade even exists," Trail says.

Based on what they've seen so far, Trail and Markley have concluded that the birds are killed and packaged in Mexico, then smuggled into the United States, where they are sold at botanicas, small shops that specialize in things like herbal remedies and religious trinkets. "It's not hard to find them," says Markley, whose investigations have focused on the Dallas area. The charms are similar to a rabbit's foot in American culture — carry it and good fortune will follow, though chuparosas appear to be specifically for amorous pursuits. Markley has been told that they are sold to help soothe the heartbreak of grieving widowers and help adulterous Romeos avoid chance encounters between their wives and mistresses. Mostly, though, they're meant to help lonely-hearted singles find their soul mates.

Trail worries that the black market for these love charms may be vast. In Mexico, where the spiritual legacy of hummingbirds stretches back to the Aztecs, the trade appears robust. Among the more troubling clues he has come across is a small sticker on the packaging of some of the charms that says "Hecho en Mexico," or "Made in Mexico," a sign that there is some sort of commercial-scale operation.

As for how many hummingbirds are killed each year, Trail can't yet hazard a guess because the trade is so new to investigators and information is hard to come by. In the only known study of the trade, researchers counted 655 charms during visits to Mexico City's Sonora Market. Many of the vendors interviewed for the study said the birds are killed by slingshot and collected from the states near the center of the country, including Querétaro, Hidalgo, and Puebla.

Trail knows all too well that fighting any type of wildlife trade comes with logistical, financial, and cultural challenges. He has begun collaborating with Mexican ornithologists who know of chuparosas but have never considered them a conservation issue. Meanwhile, the U.S. Fish and Wildlife Service has only 250 or so special agents, which makes it difficult to devote resources to the problem.

Trail doesn't know for sure when he is going to walk away from the forensics lab, but he's hoping that the service soon hires his replacement so he has at least a year or two to share the wisdom he has gleaned from the many cases that have passed across his desk. For a man who has devoted his career to protecting birds by identifying them in death, a sense of finality can seem elusive. "There are a couple of trade items that I've come across in my career that I feel are a little bit unresolved or that I would like to have some closure on," Trail says. "One is the chuparosas."

Excerpted from an article that originally appeared in Audubon magazine. Reprinted with permission.