PhD thesis

On 30 October, I will defend my PhD thesis entitled ‘Seabirds linking Arctic and ocean’. A PDF file of the thesis, excluding some chapters that are not yet published, can be downloaded below. For now, only the abstracts of the not-yet-published chapters are included; after publication of the last four chapters I will add the entire texts. Hope you enjoy reading it!

van Bemmelen – 2019 – Seabirds linking Arctic and ocean – part



30 October: Robs’ public defence

Dear all,

After five PhD-years, 13 field seasons and walking several thousand kilometres across the tundras of Ammarnas and Slettnes, I am very happy to announce that on 30 October, 11 AM, I will defend my PhD thesis entitled ‘Seabirds linking Arctic and ocean’ in the aula of the Wageningen University, Generaal Foulkesweg 1, Wageningen.

This is a public event, so anyone interested in skuas and phalaropes, or seabirds in general, is warmly invited!

Thanks to all who have helped me to get here. It has been an incredible journey!

All the best, Rob


Eastern Bonelli’s Warbler article in Dutch Birding

In the latest issue of Dutch Birding, a birding magazine with a focus on rarities, identification and distribution, a short article appeared about the Eastern Bonelli’s Warbler I found last year close to where I live. This bird, which was present for a single day in the dune reserve ‘Noord-hollands Duinreservaat’, was the fifth record for the Netherlands and the first twitchable since 1983. The fifth? Well, probably the fourth, as the first two records were accepted as separate records but are likely to refer to a single bird… Anyway, the species is clearly very rare in north-western Europe. An overview of records (thanks to Łukasz Ławicki for compiling these records), showing their temporal and spatial distribution, is included in the article. The article can be accessed at Research Gate, and some pics and sound-recordings at


Sonogram of the song of the Eastern Bonelli’s Warbler Phylloscopus orientalis, Noordhollands Duinreservaat, Heemskerk, Noord-Holland, 14 mei 2018. Note the descending second parts of each element, which distinguishes orientalis from bonelli.


New paper: migratory divide in Red-necked Phalaropes

In October 2015 at the 2nd World Seabird Conference in Cape Town, South Africa, an international collaboration was started to combine geolocator tracking data of Red-necked Phalaropes from breeding sites across the Western Palearctic. Now, a joint paper is published in Frontiers in Ecology and Evolution, showing a migratory divide between populations from Greenland, Iceland and Scotland migrating to the eastern Pacific, and populations in Fennoscandia and Russia migrating to the Arabian Sea. Especially the western route to the Pacific is amazing – a migration route not shared with any other Western Palearctic species. Phalaropes using the two routes and wintering areas differ in migration strategies and also in the amount of movements within the wintering area. Only few studies have shown such diversity in movement strategies among subpopulations within a species.

It has been a tremendous job to collect all this data, especially because Red-necked Phalaropes are far less site-faithful than, for example, Long-tailed Skuas, albatrosses or other seabirds. Out of 10 geolocators deployed, on average 3 were resighted and recaptured. Even if recaptured, things can go wrong: some loggers failed prematurely and others were lost. Considering the effort required for each and every logger, the paper is also a testament to the willingness of people to share their data and the power of international collaboration!

Hence, thanks to all collaborators, in particular Yann Kolbeinsson, Olivier Gilg, Jose Alves
Malcolm Smith, Aleksi Lehikoinen, who led the fieldwork at the other sites.

Please read the full paper here.

New paper out on primary moult in northern hemisphere skuas

A paper I wrote with Rohan Clarke, Peter Pyle and Kees Camphuysen has been accepted for publication in The Auk, the journal of the American Ornithological Society! It can be downloaded here and is titled “Timing and duration of primary molt in Northern Hemisphere skuas and jaegers”.

The paper presents estimates for primary moult timing and duration in all four northern hemisphere skuas: Great, Pomarine, Arctic and Long-tailed Skua, including multiple age-classes (for as far as they are identifiable…). Moult data is difficult to obtain for oceanic wanderers like skuas, as they perform their moult at sea where fieldwork is costly and capturing seabirds is ‘challenging’, to say the least. Recently, people realized that molt data can be obtained from (digital) photography. With a growing popularity of bird watching, bird photographing, pelagic birding trips, and the sharing of large numbers of images over the internet, a very comfortable and cheap way to collect data has emerged. Over the past years, we collected photos of nearly 2000 individual skuas, photographed at sea or near-shore by about 600 photographers. Many photos were found at online sighting portals like and, but we were also greatly helped by many people sharing their pictures through e-mail. From these pics, we inferred the primary moult score and subsequently estimated three moult parameters: the mean start date of moult, the standard deviation in this start date, and the mean moult duration.

What we found in this study is that, as expected, larger species took longer to moult, but this also meant that larger species had a hard timing in avoiding temporal overlap between moult and migration. In general, migratory birds avoid overlap of moult and migration, but we found that Great Skua moult throughout its autumn migration! A rare strategy, possibly facilitated by a very low migration speed through an area with good food availability. Another interesting find is that among the three smaller species, their very first moult cycle took longer than later ones. As soon as they started migrating, moult cycles would run more or less parallel to adults. We suggest that this shorter moult cycle reflects a time constraint set by migration.

This study would not have been possible without all photographers willing to share their pictures. A huge thanks to them!


Moulting adult Pomarine Skua Stercorarius pomarinus, off Mauritania in November 2016 (Rob van Bemmelen)

New paper out on Northern Shoveler x Blue-winged Teal hybrids

Back in May 2014, my friends Niels van Houtum and Martijn Renders found an aberrant duck at the Westerplas, Schiermonnikoog. Its identification caused some discussion, and long story cut short, it turned out to be a Northern Shoveler x Blue-winged Teal hybrid – a first for the Netherlands. This record was the incentive for a paper on the identification and occurrence in the Western Palearctic of this duck hybrid, co-authored by Jörn Lehmhus, Steven Mlodinow, published in the latest issue of Dutch Birding magazine. Northern Shoveler x Blue-winged Teal hybrids show a set of fairly constant characters, allowing confident identification.

The occurrence of Northern Shoveler x Blue-winged Teal hybrids in the Western Palearctic is not really a surprise, given that (vagrant) Blue-winged Teal often associate with Northern Shovelers, and hybridization is common among ducks. Records of this hybrid appear fairly regular in the Western Palearctic, with most records in spring. Interestingly, records show a pattern suggesting migration along a SW-NE line, with records during spring and summer occurring at increasing latitudes as the seasons progress. In the paper, we argue that (most) Northern Shoveler x Blue-winged Teal hybrids likely originate from mixed pairs formed in Europe rather than in the Nearctic.

20140504 02 Rob van Bemmelen

The hybrid Northern Shoveler x Blue-winged Teal from Schiermonnikoog, 4 May 2014.


At least in the Netherlands, it seems that some hybrids are ‘on the radar’ of keen birders and can even entice small crowds of twitchers. These are also routinely accepted by the Dutch rarity committee. For example, there are nine records of Tufted Duck x Ring-necked Duck on the Dutch list. On the other hand, other hybrids have undoubtedly occurred in the Netherlands, but have never been admitted to the Dutch list. The best example of this is Eurasian Wigeon x American Wigeon. Although surely some hybrids likely have a captive origin, I would argue that at least these hybrids are (likely) offspring of genuine vagrants and thereby demonstrate the ‘desperation hypothesis’.

The Northern Shoveler x Blue-winged Teal from Schiermonnikoog has been accepted by the CDNA as the first for the Netherlands, and we hope our paper is an incentive to find and document more records of this handsome hybrid. Coincidentally, the second for the Netherlands (if accepted) was found by Diederik Kok just before our paper came out!

If you are interested in reading the paper, please drop me a line, or browse research gate.