February 23rd   Leave a comment

In the absence of anything new appearing this week apart from the bad weather, there is time to reflect on one of the star birds that we have with us every winter. You see them reliably on Balcomie Beach and occasionally in Roome Bay – tiny very pale grey and white shorebirds running along the surf line on sand or fine mud – sanderlings. I have always been intrigued by sanderlings ever since I started bird watching when a more experienced birder (well they all were then I suppose) told me of a study that had worked out that sanderlings must use more energy feeding than they could possibly ever gain because of their continual running about. If you have watched sanderlings for even just a few minutes you will know why they might have drawn these conclusions. A sanderling’s lot is to chase the small waves in and out, continually pacing – and often sprinting – along the water’s edge in search of tiny prey that gets washed in by the tide. Clearly the scientists doing the study got their sums wrong. They do dash around a lot but they eat a wide range of often large prey, probing for shellfish and worms, and taking small crabs when they can get them. And they are probably very well adapted to conserving energy in cold environments to see to the other end of the energy balance equation. Certainly they can stand the cold. Sanderling breed almost as far north as it possible for anything to breed. I have only seen one pair of breeding sanderling, on a ridge just above the still frozen sea in June in Alaska. I was at the most northerly point of Alaska at Barrow, yet this pair of sanderling were breeding at one of the most southerly points of their range. I remember exiting the area very quickly because I thought a darker shape out on the sea ice was a polar bear: it didn’t feel to me like balmy southern climes.

Sanderling on Balcomie Beach

Sanderling on Balcomie Beach

As well as their supreme cold adaption sanderlings also have to deal with the heat at times. Many sanderling winter much further south than Crail and I see sanderling feeding just as happily in the heat haze of an African beach as on Balcomie. Sandy beaches look pretty much the same the world over (they all have sanderlings on them for a start) but that energy budget calculation must be completely different for a tropical wintering sanderling. Overheating because of all that running must surely be the issue. And the energy required to keep warm when they are not feeding will be neglible. Then this energy budget framework begins to make sense of it all – if you are running around a lot you keep warm as a by-product, and if you migrate all the way from Svalbard to Senegal it may take a lot of energy, but once you get there your costs will be very low for the winter. Life’s a trade-off (…and then you die): I wonder if a Crail sanderling that only migrates 3,500 kilometers from Ellesmere Island to join us, but that has to dash about all winter uses a similar amount of energy to a Senegal Sanderling that migrates more than 7,500 kilometers, but which can take it a lot easier when it gets there. The temperature transition for a tropical sanderling in the spring must be a thing as well. From 40 degrees to 10 below, potentially in just a few days. Birds, and shorebirds in particular, really are amazing things.



Posted February 23, 2017 by wildcrail in Sightings

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