Watlas receiver tower. Photo: Eddo Hartmann

WATLAS uses a novel tracking method that allows for smaller and cheaper tags. These tags are temporarily attached to the birds’ backs and transmit a signal every 6 seconds. Positions of the birds are then calculated from the differences in signal arrival-times at receiver stations. In 2017, we started WATLAS with a pilot study and 5 receivers. Now, in 2020, we have 26 receivers that allow tracking shorebirds in a large part of the western Dutch Wadden Sea in real-time. An important aspect of the WATLAS fieldwork is constructing the temporary receivers on the mudflats. With this blog, the WATLAS team will share their experiences and show what field work they do.

Monday 27 July | You can't always get what you want to

Due to the tide times, Sunday night would be our last chance for catching. The weather that night left us waiting until the very last moment to decide that we would not do a catching attempt. There was a strong wind, which complicates catching by causing the nets to make whistling sounds, and causing birds to fly faster and potentially getting injured when flying into the nets.

A windy but beautiful Sunday evening

This meant that our field trip yielded only four birds, but of course you never know this beforehand. If the changes are big enough that birds will be caught, attempting a catching trip is worthwhile! It also meant that all four of us would be leaving Richel with the boat that would come to pick us up on Monday morning; if we would miss that boat, we’d have to stay until Friday for the next boat… So we packed most of our stuff around midnight, and the next morning got up at 6:00 to finish packing, cleaning and, most importantly, disassembling the mist nets. Luckily, this all went fine and, as agreed, Klaas-Jan came to pick us up with the repaired Stern. We were back at NIOZ around 15:00; time to rest but almost time to start preparing the next catching trip too, which will be halfway August!

Disassembling the mist nets Unloading everything in the NIOZ harbour

Sunday 26 July | Measuring the bird movements

By Hans Linssen

On the next morning, we set up the tent unit on the Wadtoren to test the exploration behaviour of the knots we caught. In this unit, which closely resembles the exploration experiments at the NIOZ, a red knot is let into a pyramid shaped mobile room that has four trays of sand standing in a shallow layer of sea-water, resembling foraging patches emerging just above the water level. The exploration measurements last 20 minutes per bird that we film with a camera attached to the ceiling of the unit. From the video footage, we measure the movements of the bird on and between the sand patches; we ask whether the focal bird stands still in one of the trays, or does it go around, does it probe in all trays, what is it’s speed? This is the measure of exploration, as a personality trait. Before being released again, the knots are equipped with WATLAS tags, enabling us to follow them out there in the Wadden Sea and link their personality with foraging movements in the field.

 Experimental room, with four trays of sand for the knots to explore Providing the knots with WATLAS tags… …and releasing them again!

Friday 24 July | First catching expedition of this season

The field work for constructing the receiver stations has been completed, and we have moved to the next phase. This weekend, Selin Ersoy (PhD), Luc de Monte (catching expert), Anne Dekinga (catching expert), Hans Linssen (guest researcher) and Nino Maag (guest researcher) were at Richel to catch birds. Hans Linssen, Selin Ersoy, and Nino Maag have written a blog of their first day.

The team desperately waiting for Anne…

At 10:00 on Friday, we had the Stern all packed and we were off towards Richel with Stern captain Wim Jan! The goal of this trip was twofold: catching and ringing red knots, and also equipping a number of knots with WATLAS radio transmitters and testing their exploration behaviour in a provisional experimental set up. With the sun shining in a bright blue sky, spirits were high but none of us were prepared for what was about to happen. A couple kilometres from Richel, one of the Stern’s engines suddenly broke down and we were left floating on the open water for a while. Luckily, team Canutus came to the rescue and picked us up with their ship (which is also their home), to drop us off at Richel’s wadtoren around 14:00. At the same time, Wim Jan sailed the Stern back to Texel using only the one remaining engine. After setting up camp at the wadtoren, the mist nets were put up and between 01:00 and 02:30 in the night, we did two rounds of catches which yielded four knots and 14 sanderlings. Not the numbers we hoped for, but still valuable! During our rounds, we were accompanied by huge amounts of sea sparkle (Noctiluca scintillans, dinoflagellates that exhibit bioluminescence when disturbed), providing our night with a glowing edge.

…to come and rescue us. Expedition saved! Scouting for knots around the Wadtoren.

Tuesday 21 July I Day 9

By Allert Bijleveld and Christine Beardsworth

After breakfast, we set sail towards the NIOZ harbour, located in the South of Texel. We sailed past our southernmost temporary receiver and into the deeper waters of the Wadden Sea. Again, it was nice weather which meant smooth sailing for us. With a flat hull and draught of only 1.10 m, the Navicula is designed to navigate the shallow inter tidal zone of the Wadden Sea and bad weather can make for quite a rocky ride. We have been very lucky with the weather for the entire week and it has meant that we have finished our fieldwork three days early.

When we arrived at the harbour, we unloaded our equipment from the ship, and into a NIOZ van, which we took to the institute before most of the team went home for the day. Only the crew remained to offload the heavy equipment and service the ship.

To be continued...

At the end of this week, the WATLAS fieldwork will move onto the next phase for this season, when Selin, Hans, Nino, Luc and Anne will go into the field to catch red knots, measure their biometrics and physiology, assay their exploratory behaviour, and attach a small WATLAS tag to their backs. Combined with the work that we did the past eight days, we will then be able to track these birds and find out where they go in the western Wadden Sea.

Monday 20 July I Day 8

By Allert Bijleveld and Christine Beardsworth

We went out again early this morning to set up our final receiver station. Allert went to pick up a journalist, Anna van Kessel, from the Texel shoreline and brought her to the build site. She will write about the WATLAS project and about our fieldwork this week. We showed her how we build receivers, but unfortunately, we were unable to finish the receiver completely as the WATLAS unit was being fixed by Frank at the NIOZ workshop. After the rest of the build was completed, we all went back to the Navicula for a coffee and showed Anna around the ship.


That's efficiency

We got a call from Frank to say that the unit was ready at about 10 am (that’s efficiency!) and Luc, a technician for NIOZ, brought it to the North of Texel where Allert, Anne van Kessel and Christine met him on a beach, filled with sunbathing tourists, to collect the unit. Although we attempted to complete the station, the water was now too shallow to get the rubber boat to the station. Therefore, we sailed back to the Navicula for lunch, after which Allert dropped Anna off on Texel.

Ship office 

At times when we are unable to work in the field, we can do office work on the boat because there is a sporadic internet connection. This week the researchers, Allert and Christine, were able to attend their group coffee meeting over Microsoft Teams, and had a productive chat with the students that study movement ecology with Allert.

Ready to detect

In the evening, we were able to reach our final receiver station! Christine and Allert set off and had no problems setting up the stations. We checked the app to see that the receiver was working and set off back to the Navicula. We were done! Every receiver is now up and working, ready to detect red knot locations. The only thing left is to tag the birds with the lightweight WATLAS tags, which we will begin next week. For now, we will celebrate a successful week before heading home. Because of the ‘wantij’ (the divide between tidal basins), we must wait for tomorrow’s tide - that is slightly higher - to set sail.

Sunday 19 July I Day 7

By Allert Bijleveld and Christine Beardsworth

Another early start this morning to erect our penultimate receiver station. The whole team went to the location, just off the northern coast of Texel and Team Canutus started fixing the scaffold to the seabed. Nearby, there is a protected area from which interested seals came out to investigate our activities. Both grey seals and harbour seals watched us build the receiver between their foraging bouts in the gully. The receiver was built quickly, and we headed back to the Navicula. 

Fingers crossed

Shortly after our return to the Navicula, it was high tide and we set off to sail closer to Texel. Hein was leaving the ship and he had offered to take our broken WATLAS back to Den Burg. From Den Burg, our colleague Luc could bring it to NIOZ the next morning so that Frank could fix it. We hope to get the unit back tomorrow afternoon so that we will be able to successfully deploy our final receiver station. Fingers crossed!

Trial and error

Our final task of the day was to test a new method of building stations so that we can track birds throughout the year. Normally, we deconstruct the temporary receiver stations in November before they are destroyed by winter storms and sea ice. For stations to stay out year-round, we must use more robust mounting method than the scaffolds we currently use. We found a 7 m steel pole with a diameter of 32 cm diameter at the NIOZ shipyard, which should withstand the forces of nature year-round. But first, we needed to test whether the onboard crane could safely lift and manoeuvre this heavy equipment in place on the mudflat. After a bit of trial and error, we concluded that this new method should be possible to use in coming years. Now, we need to think of ways to get funding for buying these heavy-duty poles.

Heading home 

With incoming tide, the ship lifted from the seabed and we sailed towards Texel where, tomorrow morning, we meet a journalist who plans to write an article on our work. As the sun was setting, we had some spectacular skies against the backdrop of Texel with its beautiful lighthouse.

Saturday 18 July I Day 6

By Allert Bijleveld and Christine Beardsworth

We left early this morning in another attempt to fix the receiver south-east of Griend (see blog for 17 July - Day 5). Since it was hightide, they were able to take the boat all the way to the station and Allert replaced one of the components. Unfortunately, this did not fix the receiver, which meant we needed to come back later and swap the broken WATLAS unit for repairs at NIOZ.

The 'Wadtoren'

While we were trying to fix the receiver, the Navicula and Canutus had set off crossing the ‘Blauwe Slenk’ heading towards Richel, westward of Griend. After a very bumpy ride crossing the wide gully in a rubber boat, Allert and Christine met with the rest of the team at Richel. In preparation of the catching expedition next week and building a receiver station later that day, they had just dropped off equipment at the ‘Wadtoren’. This is a hut on a pontoon that can be placed anywhere on the mudflat and serves as a base for our expeditions, citizen scientist bird watchers, as well as Natuurmonumenten’s Wadwachters. After the drop-off, everyone headed out to build another receiver nearby before the tide went be out. 

Twohundred cockles

Richel is a popular place for tourists, and many had sailed there in the morning waiting for the tide to go out. After building the receiver station, we headed out to the Wadtoren to mount the electronics. At low tide, many tourists were wandering around the exposed mudflat. Several curious tourists even climbed the Wadtoren to ask what we were doing. All of them were very interested in hearing about our research and amazed by the long distances these small shorebirds travel during their migrations. On the way back, Allert pointed out how rich the mudflat was with cockles, an important food source for many shorebirds. We immediately made use of this opportunity and sampled 200 cockles for an experiment at NIOZ.

Armed with a new unit

On return to the Navicula, we crossed the gully and sailed towards Griend, back to the malfunctioning receiver station. Armed with a new unit, we were dropped off by Hein, in a rubber boat, as close to the receiver station as possible before they had to walk the rest of the way. The receiver was successfully replaced, but there were new problems with the internet connection. The tide was coming in rapidly, and Hein hurried back to the Navicula for a replacement antenna. Allert quickly mounted this before the tide pushed them back to the Navicula. As we docked the rubber boat, the Navicula headed towards het ‘Eierlandsche Gat’ where we would spend the night.

Friday 17 July I Day 5

By Allert Bijleveld and Chrisine Beardsworth

Today we completed the 50 extra SIBES sampling points, which will give us valuable information on prey availability for shorebirds, as well as contributing to the long-term monitoring project of invertebrates in the Wadden sea.

Short-lived fix

Another task for the day was to fix one of the receiver stations that we had set up only the previous day. We had noticed, using the incredibly useful monitoring app designed by NIOZ software engineer Bas Denissen, that one of our receivers wasn't detecting our 'test tag'. At low tide, we walked across the mudflat towards the station. After fixing the amplifier, the station was detecting tags again and we headed back to the Navicula. Unfortunately, it seems that the fix was short-lived and we will have to return another day to collect the unit and inspect it in more detail.

Dinner on deck

In the afternoon, we travelled to the two scaffolds that team Canutus had erected two days prior and fitted the electronics. While we could see showers in the distance, the weather was perfect, and we completed the stations with no issues. As it's Friday and we were smashing it, on our return to the Navicula we decided to eat dinner outside and celebrate with a beer.

Thursday 16 July I Day 4

By Allert Bijleveld and Christine Beardsworth

Day 4 – On the morning of our fourth day of fieldwork we decided to sample more locations to add to our SIBES dataset for 2020 (see SIBES blog). We have recently noticed that, in 2019, foraging knots were moving slightly further North West and South of Griend than they did a few years ago (see encircled areas on the map). This could be because the mudflat itself has moved. The dynamic Wadden Sea ecosystem keeps us on our toes.

SIBES sampling sites
Sifting through mud

Allert took Christine on her first SIBES sampling expedition and explained everything from how to throw an anchor to sifting through mud to find cockles, worms and Baltic tellins. Their sampling was cut short however as Bram, the skipper, called on the radio to say that there was only a little time left before the depth at the potential locations for stations 5 and 6 was ideal for building.

Well oiled-machine

Team Canutus and Team Navicula went out together to build receiver 5. Because the planned location was just inside a mussel farm, the station needed to be relocated slightly. Team Canutus circled the area while sampling the water depth with their yard sticks. After some time, a shallow ridge was found with a water level of +70 cm, which was not ideal, but good enough. Team Canutus donned their waders and jumped in the water to begin building the scaffold like a well-oiled machine. In no-time, although slightly wetter than expected since some waves had entered their waders, they had built the scaffold and Team Navicula began decorating it with electronics.

Bram and Anne to the rescue

Finally, it was time to go to our last station of the day. On the way there we saw 7 grey seals foraging near the deeper regions of the Wadden sea. When we reached our destination, Team Canutus had just finished building the scaffold and we set to work adding the electronics. Unfortunately, our problem-free field season was about to come to an end. While moving one of the large batteries onto the scaffold with a pully, the handle came off and the battery plunged into the sea. Luckily, the depth was only ~1m so Bram, armed with his dry suit, dove in to retrieve it. (See the photo for his heroic efforts). However, this was not the only thing to go wrong today. In our rush to get to the next station before the tide began to recede, we had forgotten to pick up the WATLAS unit itself! Luckily, Anne came to the rescue (again) and interrupted his dinner to bring the unit to us in time to finish the station and get back to the Navicula.

Bram retrieves the battery

Shipping notice

By Bram Fey

Intensive period for the RV Navicula and crew

For this trip, we have three crew members: The skipper, a mechanic and a cook. In addition, we have room for three passengers, which would be eight in non-corona times. Because we have limited space, the crew helps with the project as much as possible including building the receiver stations. The ship is fully stocked with roughly 10 tonnes of building materials: Solar panels, windmills, antennas, large quantities of scaffolding pipes with associated couplings, 3 rubber boats and the borrowed aluminum boat “Zilvervisje” from Wageningen Marine Research. This is a flat barge with an outboard motor and steering hut. It can sail over 20 cm of water and take a lot of material with it. Crew members Hein and Bram take it to the location where the receiver stations are to be built. Cook Hendrik-Jan ensures that everyone on the ship is well fed. Over the last few days, the weather has been good with little wind. There has been the occasional shower, but this doesn’t hinder the work.

End of shipping notice ;-)

Captain of RV Navicula Bram Fey
Cook Hendrik-Jan Lokhorst
Mechanic Hein de Vries on RV Navicula

Wednesday 15 July I Day 3

By Allert Bijleveld and Christine Beardsworth

Our morning started with a visit from Wim Jan on the Stern, the smallest member of the NIOZ fleet, to pick up the equipment that we had previously collected from Griend. To the surprise of most of the team, Wim Jan also brought a mystery box with him. We got T-shirts! After PhD student, Misha, had designed a wonderful WATLAS logo, Allert ordered a batch of WATLAS t-shirts to celebrate the occasion. After a brief photoshoot, it was time for the fieldwork.

The WATLAS 2020 summer team. From left to right: Anne, Job, Anita, Bram, Hein, Christine, Wim Jan, Hendrik Jan and Allert.
More receivers

The previous day, team Canutus had been extra efficient and built the majority of the scaffold for receiver number 2, before the tide pushed them back to their ship for the night. Now, team Canutus headed off to build the scaffold for receiver numbers 3 and 4. Team Navicula sailed towards receiver 2 to finish the scaffold and attach the electronics. In the sun, the work was pleasant, and we soon finished receiver 2 and went back to the Navicula to stock up on electronics for receiver 3.

Interesting visitor

While we were finishing the receiver station, we had two interesting visitors. Two harbour seals were foraging near the boat and had a quick look at the researchers before going back to their own business. It was a nice end to another day in the field.

Tuesday 14 July I Day 2

By Allert Bijleveld and Christine Beardsworth

In the morning, we headed towards the uninhabited island of Griend and anchored the Navicula a couple of kilometres southeast of the island. Griend provides an important high-tide roosting site for a wealth of birds such as migratory shorebirds and is the focal location for our tracking project. Later in the year we will catch and tag red knots on the island, but today we went only to collect some equipment. The shallow waters around the island at high tide mean that we must wade through the water for the final stretch.

The wardens of Griend

There is a small house on Griend owned by Natuurmonumenten who manages and protects this nature reserve. From here, researchers can study the spectacular nature on and around the island. At the house, we were greeted by Date and Giny who are the wardens of Griend during the breeding season. After a nice chat, they helped us to wheelbarrow our equipment back to the shoreline so that we could load our boat.

Team Navicula and Team Canutus

The next goal for the day was building a temporary receiver station. Due to corona, the Navicula is working at minimal capacity to ensure social distancing can be maintained. However, some tasks require people to be close together, such as inserting the six-meter scaffolding poles into the dense sand. Thankfully, NIOZ staff Anne and Anita, along with their family Cornelis and Hinke, have come to the rescue with their own ship: Canutus. While we, team Navicula, had been collecting equipment on Griend, team Canutus had been building the scaffold for our first temporary receiver station of the year.

Temporary Receiver Station

After our return from Griend, we fitted the electronics to the completed scaffold: one wind turbine, four solar panels, three batteries, a light, the WATLAS antenna and finally, the WATLAS unit itself. Since the tide had started to go out, we needed to get back to the Navicula where Hendrik-Jan, the Navicula cook, had dinner ready.

Monday 13 July I Day 1

By Allert Bijleveld and Christine Beardsworth

After spending the morning loading the ship in the NIOZ harbour with scaffolding, solar panels and wind turbines, we set off. 

Our first port of call was Vlieland, to replace one of our permanent receiver stations. This particular receiver is placed in the roof of the Posthuys hotel, giving the antenna a high probability of detecting tagged red knots in the vicinity. After anchoring the Navicula offshore, crew member Hein sailed us to Vlieland and we got a taxi to Posthuys. With help from the friendly staff we were able to replace the unit in the attic.

After some successful tests (and some support from the 24/7 WATLAS Helpline – Frank) we headed back to the Navicula for the night.