Sanderlings

A visit to a a very cold Stevenston on Saturday last afforded a sighting of a small flock of Sanderlings. There were close to fifty individuals in repose on the old pipeline which runs out into the sea next to the point. They look tawnier than they should in the photograph because of the golden hour light of a very sunny winter morning.

The tide had turned and was falling and soon, it seemed that the right kind of shore had been revealed and the Sanderlings took to the wing to reach it, landing elegantly and beginning their sprints along the sea’s edge.

The beach wasn’t busy and the Sanderlings seemed relaxed – I kept my distance (so there is some unwanted pixellation in most of these images). My RSPB book tells me that Sanderlings should not be disturbed while feeding in winter. They’ve a lot of fuelling up to do, increasing their body masses by up to 60% to get them to northern Greenland or north east Canada. Some fly non-stop, others put down in Iceland for a day or two. Reneerkens et al. (Wader Study Group Bulletin, 2009, 116, 2-20) reviewed the (then) current knowledge in 2009.

There was another occasion on the east coast when the Sanderlings came to me. It was during a visit to North Berwick on a very cold November day. I was aware of a white procession in the distance at the water’s edge and I lay on the sand in preparation; in time, they passed by quite close to me. I had a much shorter photographic reach at the time but the proximity of the birds and the brightness of the day was really helpful.

I’ve never tried to video them but there is excellent resource on YouTube; I particularly liked this BTO Bird ID video which captures their frenetic activity really effectively.  I think the sequence around 0:45-1:00 must be an optical illusion. I mean, is it me or are they going backwards at speed? Presumably not but it really looks like it. I also liked Sergey Shkarupo’s video of juvenile Sanderlings (of which more later).

This level of activity raises questions about energy accounting – or the benefit versus cost of feeding in this way. I can’t do the physics but I did discover something about Sanderling prey species. Reneerkens et al. have some useful information about diet, some of the information obtained the hard way by prising apart Sanderling pellets and analysing the contents. A wildlife project based in Oregon gave me this (my italics): “Because their quarry is small and all but indistinguishable beneath the sand, sanderlings must make several probes with each dash….They tweeze the just-wetted beach because it is softer, and because the invertebrates themselves come up to feed in the wavebreak. The window of opportunity is narrow, indeed—a mere wave’s breadth of time. Sanderlings appear frenetic in their feeding simply because it is the only way to get enough to eat.”

A bit more detail came from animalia.bio : “Sanderlings feed on invertebrate prey buried in the sand in the upper intertidal zone. In North America, this diet largely consists of the isopods Excirolana linguifrons, Excirolana kincaidii, and the mole crab, Emerita analoga. When the tide is out, these crustaceans live in burrows some way beneath the surface. When the tide comes in, they move into the upper layers of sand and feed on the plankton and detritus that washes over them with each wave. They then burrow rapidly down again as the water retreats. They leave no marks on the surface, so the sanderlings hunt for them by plunging their beaks into the sand at random, consuming whatever they find. Their bills can penetrate only 2 or 3 cm (0.79 or 1.18 in) and as the water swirls around and retreats, the sand is softer; this makes it easier for the birds’ beaks to penetrate further. In the spring, when much breeding activity is taking place in the benthic community, there may be as many as 4000 invertebrates per square metre, but their average size is smaller than later in the year. The birds appear to rush madly around at the edge of the surf, but in reality they are maximising their chances of catching as many prey animals as possible when they are at their most vulnerable near the surface.”

Benthic in this context refers to the uppermost layer of seabed, irrespective of the depth of water which covers it. UK waters host different species of isopods (species very similar to wood lice), for example Eurydice pulchra (Speckled Sea Louse). Haustorius arenarius and Corophium volutator (European Mud Scud) (which look more like shrimps) are also small (sub-centimetre long) burrowers in the sand. The British Marine Invertebrates Group tell me that Eurydice is similar to the Excirolana species.

In trying to find something out about these species, I’d first headed to the bookshelf; my copy of The Young Specialist Looks At Seashore (Burke, London, 1963) gave me Corophium volutator but not the other two species and I was puzzled, but then I noticed that the text had been adapted from Was find ich am Strande? (Keller, Stuttgart, 1961). I’m prepared to believe that there may be some species variations between Atlantic and Baltic coasts, and I much prefer the directness of the German title.

My only sight of Sanderlings in summer plumage came in Shetland, fleetingly. The pure white is still there but the brown and russet spangling on the upper part of the body is delightful.

Juveniles have very dark spangling on the upper body; I’m lying in the wet again for this one, with the young bird probing away in the soft sand of Aberlady Bay.

It was with me for quite a long time before it flew away – how long and graceful the wings look. I think these are my best foot shots too – Sanderlings are the only sandpiper lacking a backward-pointing fourth toe, which isn’t easy to see in the field. I was very happy to have the opportunity.