26th November 2019 Daniel Roca

Purple Sandpiper in Catalonia: a closer look

Purple Sandpiper (Calidris maritima) is a rarity in Catalonia, with only a handful of records in recent years. Unlike Ruddy Turnstone, which uses a similar habitat in winter, this species does not visit the Mediterranean regularly. Still, a few days ago, and for the second year in a row, a Purple Sandpiper was found in Barcelona. This is quite exceptional, and has triggered some thinking about the status of the species here (even though it surely is rare), and the possibilities of finding it more often, as well as actually where to look for it.

Let’s start by taking a look at some characteristics of the Catalan coast, which act as limiting factors for the presence of the species.

Unlike the Atlantic Ocean, tides in the Mediterranean are insignificant and don’t expose extensive areas of wave-washed, seaweed-covered rocks. This means that only the thin area that remains in constant contact with the waves could be suitable for the Purple Sandpiper. A little further up, and the rock is all dry. A little further down, and it’s always underwater. Even more, in many cases this thin line has been eroded over the millennia, creating an indent in the rock along the water surface, and shaping it in an inconvenient way for a sandpiper to stay on.

Rocky coast
Click on image to enlarge

Of the approximately 580 km of coastline, more than 200 km are rocky, frequently forming cliffs that go directly into the sea, and are unsuitable for the species. The rocky coast is found mostly in the northern third of the country (Costa Brava, Cap de Creus) and, to some degree, also in the south.

Rocky coast
Click on image to enlarge

That is not to say that the rocky portion of the coast holds no potential habitat for the species. It does, at least theoretically, and would surely benefit from a better coverage by observers. Interestingly though, the much more common Ruddy Turnstone is also quite infrequent here.

Cap de Creus
Coast near Cap de Creus. Apparently good habitat… in calm conditions.

The central coast is more or less straight, and historically was composed mainly of long sandy beaches, which take around 280 km in present-day. It surely wouldn’t be a suitable habitat for the species, but man-made constructions, basically harbours, breakwaters and jetties, have broadly changed the coastline. Nowadays, these structures take up 40 km overall, scattered along a much larger portion of the coast. The way humans have modified the natural shore could be key for the potential presence of Purple Sandpiper, as we’ll see. In the photo, the original coastline of Barcelona is represented by the red line. See how different it looks today. The new structures form an intricate landscape: breakwaters and jetties run either perpendicular or parallel to the coast, sometimes attached to it, others forming stand-alone island-like elements. What was merely a long sandy beach is now a very complex architectural structure.

Barcelona coastline, historical vs present.
Barcelona coastline. Click to enlarge

But, while the numerous breakwaters and jetties could be potentially interesting for the species, they frequently hold a major problem. The wind generates waves and waves hit these exposed lineal structures, which are quite steep, rendering them unsuitable for birds except in very calm conditions. Although Purple Sandpipers contend effectively with waves, usually they don’t feed in a Sanderling fashion, constantly on the move, but prefer a more stable setting. Even on days of calm sea, passing boats produce waves that disrupt constantly the exposed areas. Under these circumstances, sandpipers may look for a more sheltered area, but the inner side of many ports and breakwaters is often a straight, solid concrete structure, where there is no possibility for the sandpipers to feed or, in many cases, even to rest, given the constant human activity.

Breakwater, harbour
Breakwater
The outer side of the steep breakwaters is frequently hit by waves, while the inner side is usually a solid concrete structure.

Now, let’s take a look at the areas where Purple Sandpipers have been found wintering, that is, where they have been comfortable enough to stay for weeks or months.

One well-known case was that of a bird spending the winter at L’Ampolla, a small village near the Ebro Delta, in 2014-2015. Observing the area that the bird favoured the most, we see that the relatively small patch of rocky coast was sheltered by the nearby harbour. If we’d zoom out even more, we’d see that the El Fangar Peninsula provides the area with extra protection from the rough seas.

L'Ampolla harbour, aerial
L’Ampolla breakwater and coast from above. Source: Google Maps

Another bird wintered in Barcelona in 2018-2019. And in this case, a careful inspection of the area reveals some interesting facts that may help explain why the bird chose this, at first glance, unremarkable spot. The big cubic concrete blocks, thrown randomly, create a complex “loose” structure with surfaces facing all the possible directions, and also with different levels of steepness, that seems to be especially favorable for the species.

Barcelona breakwater
Click on image to enlarge

Even with moderate waves, this particular type of breakwater allowed the sandpiper (as well as some Ruddy Turnstones wintering there too) to find a place to stand and to feed. When a bigger wave would come, it would be easy to just move to a nearby and more conveniently oriented block. And, in the event of rougher weather, the complex coastal structure of the area, with lots of differently placed breakwaters and jetties (shown in the Barcelona coastline photo) would allow the bird to find a sheltered area to stay.

Compare the “loose” structures formed with concrete blocks –that take more space and create more suitable surfaces–, with the numerous breakwaters built with granite rock (mainly north of Barcelona) or limestone rock (mainly south of Barcelona), which are usually quite steep and dense. These would provide decent habitat only in very calm conditions.

Granite breakwater
Steep and compact breakwater built with granite rock. Click on image to enlarge

See (below) how the inner side of this breakwater –where the bird was feeding frequently, and also where another bird has been found this year–, is less exposed to waves and as good as the outer side.

Barcelona, concrete blocks breakwater
Click on image to enlarge. Source: Google Maps

The cubic blocks have flat surfaces, but after a few years, erosion by sea water starts to show, creating small holes where the gravel utilized in the mix of concrete used to be. These are promptly colonized by many invertebrates, which very few bird species exploit. A few Ruddy Turnstones, Common Sandpipers, or the occasional Grey Wagtail.

Purple Sandpiper
Purple Sandpiper feeding on a concrete block. Click on image to enlarge.

A bigger wave may come about, but this specific type of breakwater always provides a close by block, more conveniently oriented, to fly to. No need to move long distances.

Purple Sandpiper
Purple Sandpiper

Also importantly, the “open” nature of these structures, which are somehow detached from mainland, provides an extra protection from potential predators like cats and rats, which are very common in harbours and coasts, as well as general human disturbance produced by the ubiquitous dog walkers, fishing rod enthusiasts, etc.

Purple Sandpiper, breakwater
Purple Sandpiper enjoying its blocky kingdom. Click on image to enlarge.
Purple Sandpiper sharing habitat with Ruddy Turnstone. The inner side of the concrete blocks is less exposed to waves. Click on image to enlarge
Compact breakwater, loose breakwater comparison
Comparison of the much more common compact type versus the uncommon loose breakwater built with concrete blocks, both in Barcelona. Source: Google Maps.

In summary, Purple Sandpiper is –and will always be– rare in Catalonia, as it is in all the Mediterranean. Until recently, it has not received much attention from birders, usually considering the chance of finding one very slim. It seems advisable though, to be aware of the areas where it would be more likely to turn up. While migrants will be less picky choosing a stopover site, wintering birds probably have only small pockets of suitable habitat in many kilometers of coastline, a habitat good enough to meet their needs for a longer period of time. In this regard, the structure of the breakwaters themselves, as described above, along with the greater scheme of the coast layout, are important considerations to keep in mind.

Purple Sandpiper in Barcelona
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