I was fascinated watching the aerial maneuvers of White Pelicans at the Don Edwards National Wildlife Refuge at the south end of San Francisco bay.
Five rivers feed into the 200,000+ acres of wetlands that make up the second largest river delta system in the U.S. just north of Mobile Bay in southern Alabama. The Mobile-Tensaw delta’s expanse of swamp, bog, natural rice paddies, canals, and rivers makes this area of Alabama a real biodiversity hotspot where you can find more species of fish, turtles, snails, crayfish, and oak trees than anywhere else in North America. Harvard ecologist E.O. Wilson has called it North America’s Amazon, and so it was a real treat to venture out on a small boat to explore some of the smaller waterways of the delta for ourselves.
The southeastern U.S., and the Mobile delta in particular, was a refuge for species driven south during the ice ages of the Pleistocene glaciation. Warm temperatures year-round and plenty of rainfall (averaging 70 inches per year) ensure the most equitable conditions for life to survive, and so it has in this cradle of biodiversity.
We took a car ferry to Dauphin Island which sits at the mouth of Mobile Bay, and then drove west to Pelican Point beach for a (hot) walk in the late morning sun. The beaches along the gulf coast of this part of Alabama are composed of finely ground, minuscule particles of quartz that originated in the Appalachian mountains, were ground down by erosion and river action before being transported to the gulf, where minerals were further reduced in size by wave action over tens of thousands of years. The result is an eye-blinding, fine, white sand that actually squeaks as you walk over it.
Alabama’s gulf shores are an ecological wonder!
A little Spotted Sandpiper had the entire beach of Vadnais reservoir to itself and moved slowly along the shoreline probing now and then in the mud and under leaves as I stood quietly and watched.
Spotted Sandpipers are likely the most widespread breeding sandpiper in North America, nesting from northern most Alaska to the mid-continental U.S. along rivers, lakes, and streams.
And their breeding system is particularly interesting because they exhibit a sex role reversal compared to most other bird species. Instead of the typical female role of incubation and hatchling care, Spotted Sandpiper females “collect” multiple males, laying a clutch of eggs in each male’s nest, which he will then incubate. After they hatch, the male is in charge of protecting and providing food for the chicks, while the female goes off to find another male to mate with.
Female Spotted Sandpipers arrive first on the breeding ground, establish their territory, and then compete with each other for males to mate with. Since females can store sperm from multiple matings for up to a month, the male may be incubating and tending to chicks that are not his offspring! This breeding strategy, called polyandry, is rare among birds but is found in several shorebird species, in Northern Jacanas, occasionally in Acorn Woodpeckers, and in Harris Hawks.
I watched adult and juvenile Ring-billed Gulls fish for minnows in a shallow area of the Vadnais reservoir the other day. Their acrobatic flights over the water scoping out the potential fish prey was impressive, as was the success rate of their dives. Either the fish were numerous in this area or these gulls are much better dive predators than I appreciated before. During the time I watched them they were successful in grabbing a fish about 50% of the time.
Prairie parkland landscapes are at their peak golden color now. The fall landscape is transforming daily, and with the nice fall weather lately, it’s a glorious time to be out walking around. I’ve given up trying to find the migrating birds at this points and am just enjoying the golden colors everywhere.
The Fall bird migration is in full swing here in Minnesota, and large numbers of some of the smallest migrants have come and gone already on their long journey from their breeding grounds in Canada and Alaska to their over-wintering areas in Central and South America. These are the species that are obligate insect- or fruit-eaters that simply cannot find enough to eat during the cold winters of northern North America to survive here. So they leave well before the snow flies.
Kinglets, Warblers, Vireos and Flycatchers (like the Eastern Wood-Pewee) eat an insect-rich diet most of the year, but because there are fewer insects around in fall (compared to spring), they often utilize berries, suet, and even seeds as energy sources to store fat for the next leg of their migration. Because insects and fruit are mostly water (70-80%), these tiny birds need to eat about 1.5 times their body weight each day in order to put on just 0.5 grams of fat per day. But that’s not enough to fuel a 500 mile flight to the next stop on migration, so it takes 3-4 days of constant eating and putting on fat to get enough fuel on board.
Blackpoll Warblers are the kings of metabolic physiology when it comes to putting on fat for long-distance migration. These half-ounce (14 gram) birds double their body weight before flying non-stop for 4-5 days on one leg of their journey across part of North America and the Atlantic Ocean to reach their wintering grounds in the Caribbean Islands and northern South America. That means their little bodies are 50% fat when they take off — literally, butter-balls of bird!
We tend to see a lot of songbirds, especially warblers, sparrows, flycatchers, thrushes, vireos, etc., migrating south at this time of year. But September is also prime time to see a lot of raptors as they fly down the ridgeline above Duluth and follow the rivers past the Twin Cities.
I just happened to be at Sucker Lake in Shoreview one morning when some of the local, or perhaps it was a few of the migrating raptors, tried to cash in on the numbers of jays and robins that had just arrived.
First up was a Merlin (a little falcon smaller than a peregrine but which quite likes to eat small birds). I found him far away in a tree being harassed by Blue Jays. Then he turned on them and tried to catch them, chasing them off their perches. But this excitement was all taking place too far away to get any good photos.
Next up was a smaller raptor, a Kestrel (sparrow hawk), which would have preferred to dine on smaller prey like goldfinches or small sparrows, rather than the Blue Jays that were dive-bombing it. All I got was a look through my binoculars before the Kestrel flew off and took refuge in the pines to hide from the jays.
And then a large Cooper’s Hawk flew onto a low perch and took a look at the jays but ignored their squawks, focusing on something much bigger — the Pileated Woodpecker, still minding its own business.
The Cooper’s Hawk made no attempts to nab the Blue Jays encircling it wherever it perched, and instead made several dives at the woodpecker, trying to pluck it right off the trunk of the tree. The action looked something like this:
I think the woodpecker won this confrontation, and eventually the Cooper’s Hawk flew off to pick on some, other less formidable prey.
What could be more pleasant than to sit outside on a coolish, bright sunny morning with a cup of coffee and a camera watching Ruby-throated Hummingbirds forage on Salvia flowers? The light was harsh and full of high contrast until the birds visited just the right flowers…
Soon these tiny bundles of energy will undertake a giant-sized migration south to the Gulf coast. There they will again stock up on sugar-rich nectar to convert to fat stores that supply the energy for them to cross the Gulf of Mexico (the smallest birds to do so), without stopping, to get to their overwintering sites in Central America.
Because of their high requirement for sugar during their migration, they become frequent visitors to backyard nectar feeders at this time of year. To keep these little dynamos healthy on migration, remember to change the sugar solution in your feeders every 3-4 days, so it doesn’t grow mold or bacteria.
We spent a beautiful morning walking along the St. Croix river at Afton State Park recently, and I noticed that it seems more like fall weather now, and a lot less like summer. What a difference a couple of weeks makes in the climate here.