Curlews and Sand Fleas
One of the most interesting things about birding is the unanticipated things one learns about the natural world by simply watching birds and their surprising behavior. My wife and I went to the Texas coast two winters ago and had the opportunity to visit the Padre Island National Seashore, which is one of only 10 national seashores in the USA. It is a beautiful place with nearly 70 miles of undeveloped beach on a major migratory pathway where 380 species of birds have been identified. National Seashores are a great idea, and five threatened or endangered sea turtle species nest at Padre Island.
Depending on how bold you are feeling, you can drive the full 70 miles of beach (and back) at Padre, but the fairly narrow zone of driveable ‘hard’ sand and the possibility of getting stuck in soft sand near the foot of the dunes at high tide can cause second thoughts. We drove about 20 miles down the beach before losing our nerve and turning back. The birdwatching was great, we saw lots of terns, gulls and quite a variety of shorebirds. The latter, especially the small and hyperactive sanderlings were very fun to watch. It is hard to believe those busy and entertaining little birds migrate all the way north of the Arctic Circle to nest.
It was especially cool to see curlews wading where the waves were continually churning and sloshing along the shoreline. So THIS might be one of the places where our local curlews spend the winter. If so, the TX coast is quite a change from the dry grasslands of MT where many curlews spend their summers.
I took several pictures of the curlews and watched one of them bury its entire bill down into the sand and come up with the chunky little morsel shown in the picture below. I wondered what the morsel might be because when I took walks at the edge of the surf I never saw much that was edible. The area where waves meet the beach always looks like a biological desert to me and I figured the curlew just happened to find some sort of dead shrimp swirling around or buried in the sand.
Fast forward to this past April and we found ourselves on the beautiful beaches of the Florida Panhandle. This is a great time of year to catch pompano, a very popular and tasty fish to catch along FL beaches in the spring. Lots of anglers were out with rows of big surf fishing rods staked out in the sand. I noticed many of the fisherfolk had these strange looking metal rods with metal sieves at the end which they would occasionally rake in the swirling shallows where the waves were washing out. I asked what they were doing and they said they were catching ‘sand fleas’ to use as bait.
Then it clicked… The Texas curlew was probably searching for, and catching, the same critters. So I went home and Googled ‘sand fleas’ and was quite surprised at what I found. First off, they are not ‘fleas’ at all, and they are not even shrimp. Instead, they are a very odd type of crab called ‘mole crabs’ that live buried in the sand at the waters’ edge. Mole crabs do not have claws like a normal crab, they do not bite or pinch, and they are only 1-2 inches long and are quite chunky. Their little tail looks lobster-like and they use it to dig down very quickly in the churning area along the shore where waves meet sand. One more remarkable thing about them is they have modified antenna that are very feathery. Most of the time the mole crabs are buried in the wash zone with just their eyes and feathery antennae sticking above the sand. The antennae filter plankton, detritus, and small bits of organic material from the water and this is what they eat. They live in an extremely chaotic and ever-changing environment and are acutely adapted to it. They move constantly to follow the ’wash zone’ as the tide level changes, yet one rarely sees them because they move and re-bury themselves very quickly in the area where the waves are frothy and the sand is moving. They can be extremely abundant in certain spots along the beach. The second photo shows the results of a single sieve haul from one of those hotspots. Mole crabs make a pretty good meal for a curlew or a pompano.
As is often the case in nature, there is far more than meets the eye on the seashore. It is likely that mole crabs are a very important food source for wintering shorebirds. If you are interested in these interesting little critters, a really good video with great background info can be found at: https://oceanconservancy.org/blog/2024/01/05/meet-mole-crab/
Now I know a little more about what those busy shorebirds are looking for at water’s edge on the beach.
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