Oystercatchers: Learning how and where to survive

Wednesday, August 29th, 2012

Species: Oystercatcher

Project: Fine-scale foraging patterns of Oystercatchers in the Wadden Sea

As far as we know, adult Oystercatchers are extremely faithful to their wintering site, returning to the same site year after year, and some even defend pseudo-territories there (Ens & Cayford 1996; Goss-Custard et al. 1982). A major challenge for young Oystercatchers after fledging is learning to survive and finding a good spot to spend the winter for the rest of their lives. It is only after the young birds have become sufficiently proficient at surviving that they return to the breeding grounds (usually when three years old) for the next important step in their social career: acquiring a mate and a territory to breed (Ens et al. 1995). Studying the settlement decisions of the young Oystercatchers is extremely interesting, but also very difficult, and the UvA-BiTS loggers do not seem ideal, because contact is only possible within range of the wireless network. However, due to the growing number of scientists in the Dutch Wadden Sea who know the tricks of the trade, we now have some very nice data from a “settling” young bird carrying an UvA-BiTS logger.

On 2 August 2011 we caught several Oystercatchers with mist nets on the feeding grounds of the Balgzand tidal flats, where we also study the birds with a camera.  [Fine-scale foraging patterns of Oystercatchers in the Wadden Sea]

We lost contact with a few birds over the course of winter, including an individual designated LB-LAGC. The last time we received data from the bird was on 18 November 2011. However, on 14 August 2012 the bird was spotted by Roeland Bom on Richel, a sandbar 40 km to the northeast of Balgzand. The Navicula, a research vessel from the Royal Netherlands Institute for Sea Research (NIOZ), transported a mobile base station to Roeland, and in the course of several days he managed to extract all the information from the bird. Below is the story that emerged.

When LB-LAGC was caught and marked on 2 August 2011 it was diagnosed as a bird in its second calendar year, i.e., approximately one year old. It never returned to the low-tide feeding area where it was caught (the closest it came was 3 km), but remained to feed and roost on the eastern part of the Balgzand. It left the Balgzand area on 30 November 2011 and moved 30 km to the northeast. The figure below shows the areas that it subsequently visited and also lists the dates that these areas were visited.

Date range Location Color
2 Aug 2011 – 30 Nov 2011 Balgzand (confirmed by visual observations – Wim Tijsen on 4 and 9 September 2011) yellow
30 Nov 2011 – 28 Mar 2012 Afsluitdijk dam near Kornwerderzand (confirmed by visual observations – Dirk Kuiken on 15 February 2012) green
28 Mar 2012 – 31 Mar 2012 Richel, short stop on Griend when moving from Kornwerderzand to Richel red
31 Mar 2012 – 24 Jul 2012 Griend blue
24 July 2012 – 23 Aug 2012 Richel (confirmed by visual observations – Roeland Bom on 14, 15, 17-19 August 2012) magenta


After leaving Balgzand the bird visited three different areas: Kornwerderzand, Griend and Richel. Basically, the bird spent in each case many weeks in the same area measuring a few square kilometers. Maybe that is the time needed to obtain a good estimate of the quality of the feeding area. However, the quality of the area also depends on the pressure of conspecific competitors. In the Exe estuary, young birds move to the best mussel beds when the competitively superior adults are away to breed, but most move off again when the adults return at the end of summer (Goss-Custard et al. 1982). Thus, it is possible that the young birds learn the location of good feeding areas in summer and experience the pressure of competitors in winter. Our bird spent its first summer and part of its second winter on Balgzand, but decided to move on. It spent its second summer on Griend, but moved on to Richel at the end of July, the time that the adult birds return from the breeding grounds. Maybe feeding conditions around Griend were good as long as there were not too many competing adults. So far, our bird hasn’t spent a full summer and full winter in the same place and clearly hasn’t settled. It would be great if we could keep track of this bird and see where and when it finally settles. And if it didn’t really settle, that would be very interesting to know too, as we would need to add a “gypsy” strategy to the possible career strategies of the Oystercatcher.

Ens, B.J. & Cayford, J.T. 1996. Feeding with other Oystercatchers. In: The Oystercatcher: From Individuals to Populations (Ed. by J.D.Goss-Custard), pp. 77-104. Oxford: Oxford University Press.

Ens, B.J., Weissing, F.J. & Drent, R.H. 1995. The despotic distribution and deferred maturity: two sides of the same coin. The American Naturalist, 146, 625-650.

Goss-Custard, J.D., Durell, S.E.A.L. & Ens, B.J. 1982. Individual differences in aggressiveness and food stealing among wintering Oystercatchers, Haematopus ostralegus L. Animal Behaviour, 30, 917-928.

Goss-Custard, J.D., Durell, S.E.A.L., McGrorty, S. & Reading, C.J. 1982. Use of mussel Mytilus edulis beds by oystercatchers Haematopus ostralegus according to age and population size. Journal of Animal Ecology, 51, 543-554.

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