Red hawk down
ID tags, lab work helping clear up mystery of raptor found dead near Hot Springs
A male red-tailed hawk with a metal band on its ankle and large circular tags with the number 146 attached to each wing was found lifeless Jan. 12 at the John and Donna Simpson Preserve off Amity Road south of Hot Springs.
By using data released by the researchers who banded the bird, information about such hawks from the Cornell Lab of Ornithology, an X-ray of the hawk and information about the necropsy by the Arkansas Livestock and Poultry Commission’s laboratory, it’s possible to piece together a sort of obituary for the well-traveled bird.
Hawk No. 146 hatched in spring 2011 to monogamous parents who lived, more than likely, in a forested area of northern Illinois. Its first home, a nest its parents built of twigs, was lined with bark — and perhaps with corn husks since these hawks lived in the heart of the Corn Belt. That large nest was likely 40 feet high in a tree or even higher if they used some man-made structure.
The egg from which Hawk 146 hatched was pale brown or purple and about two-thirds the size of most grocery-store chicken eggs. It was incubated primarily by the mother and broke from its shell 28 to 35 days after she laid the egg. It may have had as many as four siblings, but it is doubtful all of them survived into adulthood.
Their father fed the nestling hawks (called eyasses) mostly mice, rabbits and other small mammals.
Forty-five days after hatching, in early or mid-summer 2011, Hawk 146 took flight and began life on its own.
In October 2011, fully grown but not yet sexually mature, Hawk 146 was captured at O’Hare International Airport in Chicago by a team of U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) wildlife services researchers, who were studying ways to prevent collisions between raptors and airplanes.
Capturing, tagging and relocating the hawks is an alternative to shooting them, which is done at many airports (see, for instance, bit.ly/2kRTeeR).
Among the questions the researchers wanted to answer were:
If a bird is trapped and removed from a busy airport, is it likely to return?
At what distance should a bird be relocated to reduce the likelihood of its return? 25 miles? 50 miles? 100 miles?
Which birds can be relocated most successfully? Young ones or older ones, males or females?
Is it better to relocate them in breeding season or some other time?
Shortly after Hawk 146’s capture, researchers put a metallic ankle bracelet on its right leg and nylon tags on the upper side of each wing, with the number 146 written in indelible marker. The red-tail was taken to a park in Whiteside County, Illinois, adjacent to the Mississippi River (114 miles west of O’Hare) and released.
At that point, the thread of the bird’s history snags. Had its development followed the life cycle of most red-tailed hawks, it could have found a mate, fathered four clutches of eggs and raised young between 2013 and 2016. But at some point in this period it ingested, as prey, some creature with lead in its body, likely a rabbit or squirrel.
Dr. John Simpson, a Hot Springs primary care physician, found the dead raptor on a large wooded plot that is owned by the Arkansas Nature Conservancy at Trap Mountain south of Amity Road. He donated much of the 880 acres to the conservancy, and he regularly checks the property. He is trying to restore it to its native state by removing invasive plants.
On one of these maintenance trips, he found the dead hawk lying in pine straw beside a narrow logging road.
“I saw the white tag and thought it was litter, so I stopped to pick it up,” he said. “It may have been there when I passed earlier but I did not see it, or it may have fallen dead at that place while I was farther east on the road.”
The red-tail had no apparent injuries. It was not stiff, and it did not have the stench of death.
“Since I was going to the Garland County Audubon Society meeting that night, I put the bird in a black plastic garbage bag and took it along to see if anyone there could tell me anything about the large vinyl wing tags,” he said.
Besides the identifying number, a bracelet just above the clenched talon had the phone number of the bird-banding registry where Simpson could report his discovery. From the Bird Banding Lab at the Patuxent Wildlife Research Center in Maryland, Simpson learned that the hawk had been banded and fitted with the wing tags in 2011.
When he showed the carcass at the Audubon meeting and later when photos were posted on ARBird-L, a University of Arkansas-sponsored listserv, other birders expressed concern that the wing tags — patagial tags — had contributed to the bird’s demise. Expert opinion, however, is that was not the case.
Karen Rowe, bird conservation coordinator with the Arkansas Game and Fish Commission, contacted the banding researchers and shared with the listserv what she learned from Travis Guerrant, assistant state director of USDA APHIS Wildlife Services in Springfield, Ill.
“Given that the hawk was over 5 years old when it died,” Rowe wrote, “it is highly unlikely that the patagial tags on the hawk’s wings had a negative impact on the hawk’s survival. Mr. Guerrant said that they banded over 600 red-tailed hawks and had no issues caused by the patagial tags.”
(A manuscript describing Guerrant’s research team’s methods and findings has been accepted to appear in a future issue of the Journal of Wildlife Management.)
Riveting vinyl-coated nylon cloth tags (with the flexibility and feel of a shower curtain) to wings in a manner approved by the U.S. Geological Survey is a common practice in avian research, particularly among larger birds. The methodology has been used by researchers in Arkansas on swans and vultures. Robert Hawkins, past president of Wildlife Materials Inc., confirmed that the patagial tags are much cheaper than radio transmitters and associated tracking equipment. Given that the researchers around O’Hare captured more than 600 birds, it represents a significant savings in research dollars.
A cursory review of wildlife research journals found no articles that empirically demonstrated that patagial tags limited bird flight or survival, but there are many research reports that demonstrate birds wearing patagial tags have survived in the wild for decades.
“The bird, at 5 years old, had already outlived many of its cohorts,” Rowe told this reporter. In fact, it had already beaten the odds against redtailed hawk survival when it was banded in 2011. Mortality rates for first-year raptors are high — “around 80 percent,” Rowe said.
She added that the Game and Fish Commission receives many reports of dead hawks, “and we cannot investigate them all because mortality is a normal and necessary part of the natural system. We do investigate hawk deaths due to illegal activities such as shooting or possible poisonings.”
The most common causes of death, she said, turn out to be collisions with powerlines or vehicles, lead poisoning, illegal shooting, or infection with the fungal disease aspergillosis or other avian diseases.
The Arkansas Livestock and Poultry Commission’s laboratory did a necropsy on
the hawk. A few test results were still pending at press time, but the lab allowed the Game and Fish Commission to release its preliminary finding.
“While some people wanted to implicate the patagial tags as causing the bird’s death, the preliminary necropsy report’s heavy metals tests indicate that the hawk died of lead poisoning,” Rowe said. “Liver lead levels higher than 6 parts per million (ppm) are considered lethal. The hawk’s liver lead level was 142.1 ppm.
“Birds of prey get lead poisoning by ingesting animals or fish (or parts of animals and fish) that contain lead fishing tackle such as sinkers, or lead ammunition such as lead shot or lead bullet fragments.”
Rowe told the Arkansas Democrat-Gazette on Feb. 17 that she wouldn’t be surprised if the outstanding test results show that a bacterial or viral infection played a secondary role in the hawk’s death.
“It is very common to see raptors with lead poisoning also contract respiratory infections because the lead has compromised their immune systems,” she said.
Lead poisoning also can lead to collisions.
“Earlier this month, one of our rehabilitators took in a bald eagle that had serious injuries from a vehicle collision,” Rowe told the Democrat-Gazette. The Game and Fish Commission pays for lead testing and lead poisoning treatment for all the eagles taken in by Arkansas rehabbers, so the rehabilitator’s veterinarian sent the eagle’s blood sample to the Livestock and Poultry Commission lab.
The numbers used in blood tests are different from those used in liver tests. In bird blood, less than 0.1 ppm is considered “background noise” — normal. Between 0.1 and 0.2 ppm indicates exposure to lead but not poisoning (i.e. lethal by itself). Above 0.2 ppm is lead poisoning, a lethal exposure.
“The eagle that was hit by the vehicle had a blood lead level of 0.41,” Rowe said. It died in a few days.
She believes the eagle was scavenging along the road because it was too impaired to hunt.
She added that “the remains of wild nongame birds
should be left where they fall. It is against both state and federal law for unlicensed people to possess these birds or their feathers” under the Migratory Bird Treaty Act and AGFC Code of Regulation 14:01. She explained that “dead birds are an important part of the ecosystem, just as the live ones are.”
Carrion, in the form of dead birds, is part of the diet of vultures, opossums, many
insects and eagles.
If a coyote, fox or domestic dog had eaten this particular red-tailed hawk, it too would have been at risk for lead poisoning.
Hawk 146’s patagial tag mounts and a metal ID bracelet are seen in Dr. John Simpson’s X-ray. Simpson found the redtailed hawk on Nature Conservancy land south of Hot Springs.