that everybody thinks about as being, literally, the treasures of our continent. And these are places that we tend to put National
Park boundaries around and say we've embraced these as the great timeless centers of North
America. We have one of these centers absolutely every
bit as important, arguably more so from a living standpoint, in the delta system. The Mississippi Delta is one of the richest wetland
communities on planet Earth, fed by a half a continents worth of nutrients that are coming
down the river and then spread out there across these different habitats, obviously gaining
energy from the sun in these shallow water environments.
The total biomass, just the amount of living
organisms that is in there in the water is beyond imagination. You can see that because some of these breeding
colonies of birds have thousands and thousands of breeding pairs, packed together just in
the tops of a few mangroves, just trying to get enough space to raise their babies; and
they're raising two or three babies each. And what are they doing there? Why are they there? Every one of those is out there spending the
day sampling the fish, sampling the invertebrate community, sampling the snakes and turtles
and frogs. So that huge community is telling us that
the delta itself, the marsh systems out there are teeming with life.
As you go down through the delta you start
from one of the most iconic American habitats that there is: the cypress swamp forest of
the south. Wading birds, various species of heron and
ibis love to roost in these trees. Those wading birds will spend the day dispersing
out into the surrounding swamps, feeding on fish and frogs and so on, then coming back
together and living overnight in a squawking madhouse in the top of these trees. Just downstream, so to speak, from the cypress
forest but still in that freshwater environment of the upper delta you get freshwater marshes.
The deeper water areas of the freshwater marshes
out there are of course enormously important as wintering grounds for North Americas
duck populations. A lot of the big rookeries of wading birds
along the Mississippi Delta are right there at that interface between fresh and salt water. When you get farther down into the pure saltwater
marshes these are places that looks like just nothing but grass but actually are enormously
diverse in terms of their invertebrate fauna, which we use as a rich fishing industry and
shrimping industry, but which those birds -- they're going out there and feeding on
every one of those different size classes of organisms. Ultimately all of those are fed by the huge
fertility and productivity of the marsh systems that are right there at the interface between
the delta and the sea.
The amazing thing about the barrier islands
that are off the delta is that that's where the beaches are, and those barrier islands
supply the bulk of the habitat on which these birds breed. The barrier islands aren't very big. And yet there's tens of thousands of pelicans
and skimmers and terns and gulls that are trying to breed out there, and so one gets
these enormous, dense breeding colonies. And there's one big dominant reason for that:
the seabird strategy is to nest on places that are very, very hard to get to for a predator.
And so, where you have concentrations of island
like that in amidst all of this unbelievable diversity of food, you get these just staggering
colonies of birds. These barrier islands are actually pretty
small and the kinds of birds that are using them are so diverse that the birds actually
kind of divide the habitat into strata, so to speak. The mangroves are particularly favorite places
for pelicans to both roost and to build their nests. There are also a number of herons that will
nest up in the mangroves, up in the higher things well off the ground.
When you get down into the lower vegetation,
the grasses, you get terns nesting in there and some gulls that will nest in there. And then you get out to just where its almost
just pure bare sand, and you get the black skimmer that puts its eggs right there on
the sand, nesting in quite dense colonies. These birds always are touching water: they're
wading in it, they're bathing in it, they're feeding from it, they're walking along the
edge of it. Their young are coming out of the nests and
being plopped into it.
These are birds that for their entire lifecycle
have direct physical contact with the water. The shorebird group as a whole - all pretty
closely related to each other although they go way back in evolutionary time - but they
are remarkably distinct from one another in what they do. Some of them almost look identical and yet
they do different things. They have different sized bills - some are
a little shorter-billed, some are a little longer-billed.
They have different sized legs - some are
really stubby legs, some of them are quite long-legs. And they actually have different methods of
foraging for food. So they can actually get quite specialized
with this combination of leg-length and bill-length and bill-shape and habitat. Between all those different variables you
can end up dividing the resources out there pretty efficiently and pretty finely.
There are spots where a myriad of birds drop
in both on their way south for the wintertime, but also on their way back north in the spring,
garnering resources, putting on fat, getting themselves ready to either have a successful
breeding season in the summertime or have a successful flight down to their wintering
homes further south in the tropics. So it's a stopover place, it's a place of
transition for even more birds than this huge hoard of species and individuals that we see
during the breeding season. This really is a region of the United States
that is unique on the planet in its diversity, in its importance both to the natural systems
out here and to the humans that live in the region..
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