DNA Tests Determine Whether 2013’s Injured Hawks Came From Bird Cams Nest

By Pat Leonard
August 29, 2014
Red-tailed Hawks Photo of Big Red and Ezra from Cornell Lab Bird Cams.

It was just over a year ago, on the same day, that two young Red-tailed Hawks were injured in separate accidents on the Cornell campus. One was found dead; the other was euthanized because of the severity of its injuries. Many people feared the young birds were the offspring of Big Red and Ezra, the beloved hawk pair that have nested on campus for years and have been featured on our live Bird Cams since 2012. But there was no way to tell for sure.

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It was the not-knowing that bothered Cornell University employees Christine and Steve Bogdanowicz. But unlike most Bird Cams fans, they were in a position to investigate. Steve is an evolutionary biologist who turned his expertise with DNA analyses to determine the hawks’ familial relationships. He directs the Evolutionary Genetics Core Facility at Cornell University. Christine is the Assistant Director for Academic Programs for the Shoals Marine Lab and a Birder on the Ground. These “BOGs” are a dedicated group of local, volunteer hawk enthusiasts, most of whom work on campus. They follow the birds in their spare time and report to the wider Bird Cams community.

So, were the two dead birds the offspring of Big Red and Ezra? It took hard work (all by volunteers), plus feathers, tissue samples, and another injured hawk to clear up the uncertainty. And when the answers emerged they were surprising: one yes and one no.

DNA testing confirmed that the fledgling found injured in 2013 was the offspring of Big Red and Ezra and a female. She was most likely D1, the eldest of the 2013 brood. Photo by Christine Bogdanowicz.

Steve learned that the bird found severely injured does appear to be one of the young hawks from Big Red’s and Ezra’s 2013 “D” brood. This bird, a female, was known as “D1” to the hawk cam community. The other young bird, the one that had been found dead, had been assumed to be “D3.” This bird, a male, turned out not to be related to Big Red or Ezra and must have come from another hawk nest in the area.

In October 2013 Steve began the necessary DNA work using tissue samples from the two dead juvenile hawks sent over from Cornell’s Animal Health and Diagnostic Center. His goal was to create a library of specific genetic “markers” for Red-tailed Hawks—something that did not exist at the time. During the fall of 2013, Steve developed 15 microsatellite DNA (msat) loci (locations) from the samples.

“Msats are simple, relatively short, repetitive sequences interspersed throughout otherwise complex genomes,” Steve explains. “Humans, Red-tailed Hawks, plants, and other animals typically have tens of thousands of distinct msat loci.” Finding a set of specific markers that can be used as a basis for comparison is the same technique used to identify human crime suspects or establish paternity.

To establish relatedness, Steve also needed to get DNA from Big Red and Ezra and one of their known offspring for comparison. That didn’t happen until 2014. Another dedicated BOG and Cornell staffer, Karel Sedlacek, collected feathers he witnessed drop from Big Red and Ezra and passed them to Steve. (Note: Sedlacek was issued a special permit to take these feathers. It is otherwise illegal to do so.)

Young Red-tailed Hawk "D3," offspring of Big Red and EzraE3, a fledgling from Big Red and Ezra’s 2014 nest, was also injured and is recovering at the Janet L. Swanson Wildlife Health Center. E3’s DNA sample was a crucial part of determining the identities of the 2013 hawks. Photo by Dr. Noha Abou-Madi.

Then E3, a bird hatched by Big Red and Ezra this year, was injured after fledging. The Janet L. Swanson Wildlife Health Center is caring for him and was able to provide a blood sample.

“E3 was key,” says Christine. “His sample solidified what an offspring of Big Red and Ezra would look like genetically.”

“DNA extracted from an individual hawk can be amplified through a process called polymerase chain reaction (PCR) at each of these microsatellite loci,” says Steve. Amplification means the PCR process increases the amount of DNA available, creating enough genetic material to visualize and measure. A separate test to determine gender was made possible by Laura Stenzler at the Cornell Lab’s Fuller Evolutionary Biology lab.

Sample results from 1 of the 15 microsatellite loci used in the DNA analysis. Like humans, birds receive one copy of their DNA from each of their parents. By lining up the peaks in the graphs, it’s clear that E3 received one copy of this locus from Big Red and another from Ezra. By comparison, the mystery hawk has two copies of the same allele (and thus shows only one peak). That peak does not match either Big Red or Ezra, indicating he is not related to either of them, and therefore cannot be D3. Photos: Big Red and Ezra by Christine Bogdanowicz, E3 from the Janet L. Swanson Wildlife Health Center.
Young Red-tailed Hawk "D3," offspring of Big Red and EzraDNA testing established that the fledgling found dead in 2013 was not related to Big Red or Ezra. D3 (above) may still be out in the wild somewhere. Photo by Christine Bogdanowicz.

Steve’s work established that E3 had DNA markers showing he inherited one PCR fragment (allele) from Big Red and another from Ezra at each microsatellite locus—just as humans inherit one copy of each parent’s DNA. Any offspring of Big Red and Ezra would inherit one PCR fragment from each parent for all 15 of the loci—all 15 loci have to match, as they did for E3. (The figure below shows 1 of the 15 loci.) If there is even one mismatch, that’s enough to rule out that bird as being related. And that’s what happened with the mystery juvenile originally thought to be D3.

There are many other Red-tailed Hawks in and around the Cornell campus. Some hang out near the horse paddock, others live along nearby cliffs, and still others frequent a nearby cemetery. Perhaps the mystery juvenile came from one of those groups. Steve has gotten tissue bank information for about 40 red-tails that the Wildlife Health Center has taken in since 2011. With that and any future samples gathered, he could start building up a profile of what the local Red-tailed Hawk population looks like and determine relationships from a tangle of overlapping territories.

“Now we’ll be able to focus on these 15 established markers to determine if birds come from an isolated population or if there’s gene flow between two or more populations,” says Steve. “We can learn family-level relationships and individual identity. Big Red and Ezra have produced maybe 20–25 offspring over the last decade. Are any of them back in the area as adults? I’m doing this work because I’m curious, primarily, and because of the mystery of the two dead birds last year.”

“Maybe it’s a little bit of closure,” says Christine. “There was so much hurt and angst, anxiety and sorrow. But these birds will not have died in vain if we learn from them. They’re helping us understand the family of Red-tailed Hawks that live in this area and maybe beyond.”

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