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.