Closing the gaps: Studying Spoonbill moult through photography in the Wadden Sea

by Arjen de Boer 

I find my way through the tall grasses across the reclaimed land of Lutjewad. Some horses curiously stare at the student carrying a full backpack, bright blue camping chair and folded hide tent. In the distance, a handful of Spoonbills have already gathered and are scouting the shallows for a bite to eat. I find one of my usual spots and plant some stakes into the ground, set up the tent and unfold my cheap chair. Shortly after settling in, the first flocks of Spoonbills arrive and join the few that were already there. At this point, most of them gather in the distance, near the water line, but it does not take long for the tide to come in and direct the white birds towards me.

I am here to learn about the moult of Spoonbills. We know a lot about this iconic bird, but details about their yearly flight feather replacement remain scarce. Nearly six decades ago, the matter was raised in a handbook of European birds, stating that “a more detailed examination of moult is urgently desired”. I will help fill in the gaps by photographing Spoonbills in flight and investigate their flight feather moult.

Spoonbills at the high-tide roost by Lutjewad sit out a bad weather spell.

Ater a couple of hours of photographing spoonbills, most have found a place to rest and sleep for the day. Some stay on the basalt dam jutting out into the Wadden Sea, while others rest on the elevated plains behind me. For hours on end, nothing happens and the birds simply wait until the tide goes out. Especially in bad weather, while I’m warm and dry in my small tent sipping coffee from my thermos, birds do absolutely nothing but wait, preen or sleep. Every now and then a Marsh harrier spooks the birds and with an audible whoosh all birds on the flats take off, giving me an opportunity to rattle off some shots before everything settles back to normal.

Over the course of two and a half months in the summer of 2021, I’ve taken more than 11.000 images of spoonbills, allowing me to help uncover the fascinating patterns of moult progression. Months of image processing went by and Theunis Piersma and I worked on an ever-developing story, with Wouter Vansteelant later joining our efforts. Contrary to initial expectations, we found that immature spoonbills regrow their flight feathers at a much faster rate than adults, and start their moult on average five weeks earlier. Because of this, immature spoonbills are able to replace more feathers than adults during the moulting season. Nevertheless, hardly any Spoonbill completes their moult in time before their southbound migration. As autumn approaches, immature and adult Spoonbills suspend their moult synchronously, and complete flight feather replacement in their wintering grounds. All of our findings are now published by Ardea, and Dutch newspaper Trouw devoted a nice article to our work that put Lutjewad on the map as the “Spoonbill’s changing room”.

After about seven hours, most Spoonbills and other birds start making their way back to sea, giving me ample opportunity to photograph them once more. As soon as all the birds have departed and the flats of Lutjewad are empty, I step out of my tent, give my legs a much needed stretch and head back home. 

Spending hours in a hide at a gathering place like Lutjewad, one is bound to witness intimate social behaviours. Here, famous Spoonbill Sinagote allo-preening with another, anonymous Spoonbill.

Lutjewad is one of the many magical and peaceful places located in the Wadden Sea. Thousands of birds find refuge here every day, especially during moult, when birds are in a vulnerable stage of their lives. It is imperative that areas such as Lutjewad remain protected and undisturbed, similar to breeding sites, in a Wadden Sea that witnesses ever increasing human activity.

Centre for global ecological change at the University of Groningen

Birdeyes is a science and creative centre that views the world - almost literally - through the eyes of birds. More and more birds are flying around with tiny transmitters, loggers and other high technology on their backs and legs. This generates an unimaginable amount of information. By cleverly combining such data with other sources of information, and by using new ways to tell stories and share the insights with, BirdEyes strives to open up a new knowledge network. The centre at the Faculties of Science & Engineering and Campus Fryslân aims to be an innovative part of the University of Groningen and is linked to the Rudolph Agricola School for Sustainable Development. BirdEyes, with empirical and inspirational roots in the farthest corners of the world.

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