Ryan Bourbour volunteered at the California Raptor Center from 2014-2015 when he was a Wildlife, Fish & Conservation Biology undergraduate, and has since carried over his interest in raptors to his graduate studies in Department of Animal Science, Hull Laboratory.
His latest research was published in the latest issue of Ecology & Evolution, entitled “Messy Eaters: Swabbing prey DNA from the exterior of inconspicuous predators when foraging cannot be observed.”
The study
The goal, Bourbour says, was to develop and implement a method for studying the diet of migrating raptors in order to learn about the prey raptors rely on to fuel their migration. Raptors continuously hunt while on their migratory journeys, so it is critical for researchers to understand what resources raptors need to survive this important part of their yearly cycle. The study currently focuses on bird-eating raptors—falcons and accipiters—which have high energetic demands during migration and are very active hunters en route. The method allows Bourbour et al. to investigate how important migrating songbirds are as a food source for these raptors.
The team wanted to address the challenging nature of studying the diet of these migrating raptors systematically. This task would be impossible with observational methods alone, because rarely is one in the right place at the right time to document the successful capture of prey. To address this challenge, the team developed a technique that enables researchers to collect trace DNA leftover from a previous meal by quickly swabbing the beak and talons. They were then able to extract the DNA on the swab tip and amplify the DNA sequences from the COI gene, which is a specific gene sequence known as a “genetic barcode” that can be used to identify the prey DNA to the species level.
Fortunately, every fall thousands of raptors are banded at migration monitoring stations situated along migration corridors across North America. This practice provided a unique opportunity to utilize this technique to begin to study the diet of migrant raptors. The team collaborated with the Golden Gate Raptor Observatory and their volunteer raptor banders for this part of the study and collected hundreds of samples over the 2015 and 2016 migration season from Sharp-shinned Hawks and Merlins. [Side note: members of the beak and talon swabbing component of the study often describe the swabbing process as giving the raptors “spa treatment”]. The team’s next step now that they have validated their method is to describe the prey detected on hundreds of migrant raptors, the first time anything like this will be done on this scale.
How the CRC got involved
The CRC’s role in the study was to validate the methodology itself [swabbing the exterior of beaks and talons to determine a raptor’s recent meal]. For this part of the study, Bourbour visited three resident raptors—Jack, Whistler, and Rosa—that had a known diet. He swabbed the exterior of their beaks and talons, then verified in the lab whether the collected DNA reflected what they had actually been fed.
“The exciting part was that even when the beaks and talons looked clean, I could still detect chicken DNA on the swabs for the hawks fed chicken.”
Stay tuned!
The idea of this method was first conceptualized by Dr. Josh Hull in the early 2000s while he was studying migrating Merlins in Virginia that had visible prey remains from a previous meal on their beaks and talons. The team initiated the study in 2015 and it took 3 years to develop the method of obtaining DNA in the field and processing the DNA samples in the lab, followed by publishing the method in an open-access journal for other researchers to use. However, the full study aiming to describe the diet of migrating Sharp-shinned Hawks and Merlins is ongoing, so stay tuned!
Read the full paper here