From counts to knowledge: research in progress at BRC
While Batumi Raptor Count has hosted student internships and dissertations for many years, our popularity among students of bird migration rose substantially in recent years, to the point that our Research Coordinator has been struggling to accommodate all requests. Strap in for a overview of what research is being conducted at BRC right now.
Comparing relative timing of different species of raptors between the Pyrenees (red) and the Caucasus (blue)
First and foremost, after the successful completion of our last spring count earlier this year our new chairman Tohar Tal will soon be submitting a paper on the first full-season description of Batumi spring raptor migration to a peer-reviewed ornithological journal. Now a student at University of Groningen (NL), Tohar will describe spring abundance and timing of raptors in Batumi for the first time, and also contrast seasonal flight paths through the bottleneck.
The spring data are also being included in a study of sex differences in seasonal migration timing of Pernis and Circus species at Batumi, led by Marc Heetkamp. Marc completed a literature study on this topic as part of his education at the University of Utrecht (NL) last spring, and is now proceeding with analyses.
Beyond using just count data, Elien Hoekstra is using digital photography to study the moult of migrant raptors. Elien got a great grade for her dissertation at Van Hall University of Applied Sciences this year (NL). Now a MSc student at Wageningen University (NL), Elien aspires to publish her interesting results in a reputable ornithology journal.
In addition to the more advanced projects above, several students have initiated new projects after participating in this year’s autumn count. Two of them are actually combining BRC data with high-quality count data of other sites to look at larger scale patterns in migration.
For example, some species like Black Kite are known to migrate much earlier in the western than the eastern flyway (Fig1, top panel). Michaëla Berdougo, based at Lund University (SW), obtained data from count sites in the French and Spanish Basque country — situated at the same latitude as Batumi — to investigate how common it is for different (sub) species to show differences between western and eastern flyways, and why this may be.
Isaac West, geography student at the University of Cambridge (UK), is using historic count data from SPNI in Israel from 1990-2013 and BRC data from 2011-2022 to study whether raptor migration timing has shifted in our flyway in response to climate warming. Against our expectations, his results indicate that autumn raptor timing has changed very little over the past 3 decades!
Zooming in on the Batumi bottleneck again, Joachim Pintens completed a full-season internship as assistant coordinator, and is now proceeding with a study of Booted Eagle migration for a BSc. Dissertation at Ghent University of Applied Sciences and Arts (BE). He is comparing the seasonal abundance and timing of dark morph and light morph individuals, which may offer clues about the geographic origin of these birds.
Number of flocks of different sizes recorded at BRC during standardized daily time periods (sunrise + 1h to sunset – 2h) during 11 autumn counts since 2011.
Finally, our long-time president Dries Engelen is preparing a descriptive study of European Roller migration at Batumi. The abundance, and especially the occurrence of loose but large flocks in Batumi (as many as 240 birds together, Fig2) seems to be rather unique in the world. After consulting many specialists and old literature from across the species range we’ll be writing up our findings soon.
Update: Moult study of Batumi raptors
The Batumi Raptor Count has done extraordinary raptor migration monitoring for years, but apart from all the migration data we have been collecting for so long, the bottleneck offers another interesting possibility. With the help of our volunteers with photography equipment, we are able to study the moult of the Batumi raptors.
Moult is a broad field of study which is often neglected due to logistical challenges. Moult studies require comprehensive data that is generally obtained via access to large numbers of captured birds or museum skins to gain detailed information. This is particularly difficult for birds of prey. Moult studies can give insights into difficult to study aspects of bird ecology via interactions with other life events. These studies are therefore an important application in conservation driven research. Both migration and breeding of raptors (or birds in general) have been studied extensively, but moult is a broad field where fundamental insights can still be made. To the best of our knowledge only one study has used digital photography to study moult patterns of migrant raptors at a geographical bottleneck, revealing a strong positive effect of autumn passage date on moult progression of Marsh Harriers migrating through Italy (Strait of Messina). Adult female marsh harriers showed a more extended moult and later timing of migration than adult males (Ramírez & Panuccio, 2019).
Honey buzzards, adult male and female. Both birds have moulted their P1 and P2, the female has a growing P3 on the right wing and replaced 3 innermost tail feathers. Photo by Bart Hoekstra.
As you know, the Batumi bottleneck offers access to a great number of birds that can be photographed up close, and there are always generous counters (or tourists) who are willing to share their raptor photos with us.
And that is exactly what we have been doing. Since the 2019 autumn count we have systematically collected all the photographs from counters who were willing to share them for research purposes. This means that we have several hundreds of GB’s of photos available for a moult study and we have already started collecting moult data from the photos. Collecting enough data and analysing this takes a lot of time and effort, but we hope to be able to publish our first results in 2022.
Montagu’s harrier, immature male. Primaries 1-7 are new as well as secondaries S1 and S5. Photo by David Erterius.
The aim of this study is to use digital photography at a globally important raptor migration bottleneck to quantify moult progression in a wide range of migrant raptors, and to test the association of moult strategies with species-specific traits (evolutionary lineage, migratory traits) and individual traits such as age, sex and timing of passage within species. Expected outcomes of this study are variation within genera (in relation with individual traits). Some examples: species that migrate later have more advanced moult than others. Individual traits can show us that females have moulted more feathers than males, immature birds also show more moulted feathers than adults. Furthermore short-distance migrants have more moulted feathers than long-distance migrants and partial migrants show more variation in their moult extent.
We will continue collecting photos from our counters in the upcoming seasons, so we can continue to build towards a large dataset for moult study.