Mud. Thick, gunky, suck the shoes off your feet mud. A superficially worthless and oft-derided substrate that isn't given nearly the due it deserves. If you like birds, especially shorebirds, mud is worth something. And if you are interested in the big, long-term picture of plant distribution and global ecology, mud takes on a whole new meaning.
But this big, open landscape is full of subtle ecotones, and carefully watching the different species of plovers and sandpipers will reveal distinct affinities for different niches. Yellowlegs, Stilt Sandpipers, dowitchers, godwits and other long-billed, long-legged species typically forage in the shallows just offshore from the mud.
Semipalmated Sandpipers and Dunlin often occur right at the mud/water interface. Least Sandpipers and Semipalmated Plovers will frequently forage a bit further back from the water, where conditions are a bit higher and drier.
We saw over a dozen shorebird species at Hoover yesterday, and as always it was fun and instructive to watch their various methodologies for plundering the mire of its tiny invertebrates.
And all of them share a commonality in habitat preference - they prefer the drier spectrum of the mudflats, where vegetation is starting to reclaim the barren ooze. In the above photo, we are well back from the water, and an elevational rise of just inches has allowed the mud to dry to the point where plants are forming a green carpet.
All of these plants are seed-bankers; species adapted for short-lived, irregularly appearing habitats. Their seeds are capable of decades-long periods of dormancy, entombed in the mud and awaiting the return of conditions favorable to germination and growth.
Tiny and unimportant as these plants may seem, they are actually of extreme importance over the long run. Mudflat seedbankers are frontline ecological pioneers that jump into an unvegetated niche, and begin the all-important process of stabilization. If water levels remain low for long enough, these plants help shore up the substrate enough for bigger, long-lasting plants to invade.
And even if they don't stay long, for the brief period that lovegrasses, sedges, etc. blanket the mudflats, they radically change the animal food supply of the flats. I observed an abundance of tiny insects in the plants, and even numerous jumping spiders, robber flies and other small predators. So, for birds like the Baird's and Buff-breasted Sandpipers, the vegetated upper flats provides a food-rich foraging environment unexploited by the rest of their ilk who remain in the water or fresh mud.
Distribution map of the Buff-breasted Sandpiper, courtesy Cornell Lab of Ornithology. In their global wanderings, migratory sandpipers such as this hit a lot of spots between breeding and wintering grounds. And it stands to reason that over the millenia that these birds have been flying the earth, they've been part of plant migration.
Both the Creeping Lovegrass and the Awned Flatsedge also occur in Argentina and the wintering grounds of the Buff-breasted Sandpiper and its long-haul brethren that winter in South America. There are numerous other botanical examples of this plant-shorebird connection, too.
I think it is likely that shorebirds such as the ones that I've mentioned are the dispersal agents for moving northern plants species to the other end of the globe, or perhaps vice-versa. The odd seed is certainly going to make the trip from time to time, either in the bird's digestive tract or perhaps stuck to its body. Given enough time - and they've had plenty of that - this should lead to isolation and speciation, as could be the case with the Ammannias and others.
Food for thought, and an angle that perhaps sandpipers and plovers are not given credit for although they might deserve it. Certainly very little study, at least that I'm aware of, has gone into the botanical/shorebird connection.