By Danielle E. Gerik, Caroline Van Hemert, and Colleen M. Handel
Related paper: Beak deformities in Buteo jamaicensis (Red-tailed Hawk) signal possible emergence of avian keratin disorder among raptors by Caroline Van Hemert, Colleen M. Handel, Susan Cottrell, Danielle E. Gerik, and Robert J. Bildfell. Ornithology.
Buteo jamaicensis (Red-tailed Hawks) are a ubiquitous and beloved bird across North America, commonly seen soaring over open landscapes or conspicuously perched on prominent branches or power poles along roadways. Biologists with the former Falcon Research Group had been studying these charismatic birds since the mid-1980s in the state of Washington, but it wasn’t until the winter of 1996–1997 that they first captured an unusual B. jamaicensis with a strange, elongated beak. A hawk with such a beak had never before been reported in the wild. Since that first bird was sighted, more than 100 Red-tailed Hawks with beak deformities have been reported by biologists and participatory science observers, nearly all of them along the Pacific coast of North America. Alarmingly, almost 30 percent of B. jamaicensis captured by the Falcon Research Group since 2014 have had beaks that were visibly overgrown and often crossed.
Coincidentally, or perhaps not, a parallel story was unfolding in southcentral Alaska, where Poecile atricapillus (Black-capped Chickadees) ()and several other species were showing up with beak deformities beginning in the late 1990s. This disease was termed ‘avian keratin disorder’ or AKD, for short, because affected birds tend to have multiple types of keratin issues in addition to beak deformities (e.g., scaly legs, flaky skin, occasionally overgrown claws).
After extensive testing for multiple potential causative agents, members of our collaborative research team, which included the U.S. Geological Survey, San Francisco State University, and California Academy of Sciences, discovered a novel avian RNA virus, named poecivirus, that was strongly associated with beak deformities in chickadees in Alaska and identified as the likely cause. We later detected the same virus in a single swab sample collected from a captured B. jamaicensis with an overgrown beak in Washington. Could the virus have moved from Alaska to Washington (or vice versa)? And did this detection reveal a possible causal link between beak deformities in hawks and AKD in chickadees? We don’t yet know. However, we do know that birds with AKD are moving between the two areas—a B. jamaicensis harlani (Harlan’s Red-tailed Hawk)) with a normal-looking beak banded in Washington was recaptured five years later in Alaska, this time with a significant beak deformity (see photos). When we examined affected hawks’ beaks under a microscope, we saw features similar to those found in chickadees with AKD. Also reminiscent of affected chickadees, one hawk with a beak deformity had overgrown talons. Our findings suggest a potential shared etiology, but more information is needed to determine whether these geographically distant, yet strikingly similar, occurrences are causally linked. Continued research on AKD would help resolve these and other unanswered questions.
An important goal of our work was to raise awareness about this disorder and to document new appearances of beak deformities among B. jamaicensis and other species. Understanding the spatial and temporal patterns of a disease can shed light on its cause and mode of transmission. Observers can help track affected birds by submitting reports to citizen scientist platforms, such as iNaturalist, or by reporting them directly to the USGS. Tags: long-billed syndrome, avian keratin disorder, Red-tailed Hawk, Buteo jamaicensis, disease, beak deformity