By Chris Heward, GWCT Head of Wetlands Research
GWCT staff members have co-authored a recent article, “Vocal individuality measures reveal spatial and temporal variation in roding behaviour in Woodcock”, published in the ornithological journal Ibis. Chris Heward, of the Wetlands team, lends his knowledge of the study’s focal species, while the Farmland Ecology Unit’s Niamh McHugh, who initiated the study, has a background in acoustic monitoring first honed during her study of farmland bats and agri-environment schemes. Co-authors include experts in the field of bioacoustics at Southampton University and the British Trust for Ornithology.
This study was made possible by the Dick Potts legacy fund which was awarded to a student at the University of South Wales, Dionne Jenkins, who collected and analysed the data in 2019 as her MSc thesis. The baton was then passed to the paper’s first author, Thomas Bristow, who was a placement student at GWCT in 2020, and had his plans for his final year project disrupted by the COVID-19 pandemic.
Most fieldwork was suspended that year, but Thomas went on to conduct the desk-based analyses of Dionne’s data that are presented in the paper. GWCT has a long history of supporting students and we usually find these to be very beneficial partnerships given the wide range of hard-working, enthusiastic and bright students we’ve had the opportunity to work with.
Of working on this collaborative study, Thomas said, “This project proved a welcome distraction from COVID and taking it all the way to publication has been an incredibly valuable, and enjoyable learning experience. It was an absolute pleasure to collaborate with GWCT on this and I am immensely grateful for all their support.”
Thomas’ aim was to distinguish individual male woodcock from recordings gathered using remote sound recorders (passive acoustic monitoring) by measuring imperceptible differences in their roding calls. This technology is becoming increasingly established in the field of ornithology. Thomas’ analyses take inspiration from an earlier GWCT study that first proved that roding calls varied between males.
Why is this work important? Firstly, because it improves interpretation of woodcock survey data; our results are no longer registrations relating to an unknown number of males, but can instead provide an estimate of density (i.e., males per km2). Being able to recalculate our calibration equation using remote recording devices could allow us to increase its accuracy, even tailoring it to different regions or landscapes. We also hoped that recognition of individuals would allow us ‘track’ males between neighbouring survey locations and over time; allowing us to measure the risk of double counting and monitor variation in roding activity over time.
Thomas’ hard work demonstrates the value of acoustic monitoring for woodcock, and shows that it is possible to identify some individual woodcock using this method. But this wasn’t universally true, and distinguishing individuals became more difficult at sites with lots of woodcock. The more males that were present at a site the more likely different individual’s ‘voices’ would overlap and separation would be less clear-cut. Given the increasing use of passive acoustic monitoring, this paper makes a important contribution to our understanding of its value and limitations with regard to woodcock surveys.