Saturday morning at 7:15 I drove and walked down to the south end of 24th St. It has been hot - most of the past week has been around or above 100F.. but on this morning it was a comfortable 76 F before the sun.
Walking down the shaded jeep road I felt I was leaving at my back the noise and clatter of human culture and entering a quieter saner green world. Where the path crosses over a narrow shaded ditch with cool puddles there were many tracks from last night's traffic. There cross turtles, garter and water snakes, foraging mammals and others. I walked on firm sand SW beyond a landscape debris dump. Two or three threads of gossamer woven last night touched my skin as I walked. They are tied to the surrounding 'rambunctious garden' of shaded cottonwood, willow and salt cedar saplings. There will be more gossamer as the season progresses. I walked to the junction and took the path back through the 20 feet of young thick willow stems to the open river sand bar.
On the north bank a green heron eyed me suspiciously, hesitantly deciding to fly or stay. I heard geese, looked up and was surprised to see 44 birds in formation rising, flying north.
Along both sides of the active river floodplain shaded deeper meter wide trenches are filled with minnows and dark green algae. The fish are cooler in the shade. Beaver keep some of the trenches open to flowing water.
In the ankle to knee deep main flow of the river there are many schools of hundreds and thousands of minnows. The larger minnows are limited to the deeper sections, with few of the smallest fish (fish feeding on fish likely). In the shallower ankle deep water there are the smaller minnows and in the quieter eddies the smallest fry.
The eddies and shallow waters are like estuaries: safer, warmer, relatively food filled. In the shallowest water, hundreds of thousands of aquatic corixid bugs graze on the algae (and diatoms?). It is a neat ecological zonation created by trophic ecology (?)
In the trenches a half dozen gyrinids zoom back and forth. Watching them I wonder if the reason for what looks like their continuous frenzy of motion is predator confusion. It is difficult to focus on one beetle at a time. On the far bank, the south west side, downstream from the old brown bleached snag a foot above the water, there is a larger group of 40-50 gyrinids. It would be interesting to bring a GPS unit and see if the animals along the river tend to remain in the same location.
Unfortunately seven Chrysops horseflies attempted to bite the back of my legs and ended up on their backs floating in the current. I did not see any taken by predators as I watched.
There is a group of three crows that seem to be constant companions and greeters, hanging out where my path comes down to the water. On the sand bars covered with algae there are four or five robins foraging on bugs (or minnows in the shallowest water?). A belted kingfisher flies along the SW shore between favorite perches (need to mark with GPS again) and a flock of 5-6 redwing blackbirds are just downstream. The bright redwinged male emerges as I approach what looks like a hidden backwater (nesting?) area. He gives occasional alarm(?) calls until I get closer and the females and other younger males fly up to join the first male on his snag.
I hear the distinctive killdeer call and watch a fast flying bird come swooping in for a running landing on firm smooth wet sand at the river's edge. A flycatcher likes to perch and forage from a thicket of willow branches hanging low along the SW bank. I see one great blue heron flying to a new perch in the cottonwoods. A pair of doves flies overhead twice as I walk along the wet sandbars.
Along the SW shore there appear to be four or five tiers of vegetation from the open sand bar with its covering of dry or wet algae and sparse vascular plants. The first well defined stand is of grasses and sedge and polygonum - perhaps 50-75 cm tall. Farther back is a rank of Arundo giant cane and abundant willow and cottonwood saplings, maybe 1.5 - 2 m tall. Then farther back there is taller giant cane Arundo bearing brown seed heads.. and finally there is a stand of scorched cottonwoods. I wonder if these stands are topographically delimited by the slope and shelf of the shore and levee.. or temporally defined - areas where the river has not been cutting for longer or shorter periods.
It might be an interesting sampling exercise to count all the willow and cottonwood stems within 1 or 1.5 m of the water for a distance of 10 or 20 m.. see if the data changes significantly up and downstream.
Across the wet sand from the water's edge I see a beaver's dragging of branches up into it's bankside den. The wet algal crust of portions of the sandbars looks to be highly productive.. looks to include N-fixing cyanobacteria and have plenty of biomass growth. I don't see that many herbivores feeding on it. Are they there below as larvae? Are there herbivores such as the Bembidion ground beetles that fly away before I am close enough to see them? Across the drier but not driest open sand the surface is covered with tumuli, small coin sized mounds of excavated sand connected by serpentine tracks like a snail produces. These mounds are a mystery to me.. not ants (almost no ants to be seen anywhere here).
Interesting to think about disturbance and recolonization of the algal crusts on the sand bars and along the shallow river bottom. The river bottom comprises a shifting mosaic of moving fresh sand moving/ creeping along in the current and patches of sand stable for some days, now covered and somewhat stabilized by algal growth.
Turning back at the old bridge abutment and heading back downstream along the shore and a sandy road the sun is backlighting a whole stand of 50-75 cm cottonwood seedlings and other rank new vegetation. It is a magical view revealing hidden herbivores, beetles, aphids, other insects walking on the leaves. I see the Coleomegilla ladybeetle busy searching a stem for her aphid breakfast.. and then see a heavy flying lumbering tank of a Plectrodera cottonwood borer. I follow as it flies 30 feet and can see where it lands. I picked it up and feel its strong mandible and powerful legs. After a few minutes of inspection and wonder I set the beetle back on the twig where I found it. I hear the cicada buzz and see a chrysomelid leaf beetle (by silhouette) trotting off to find a good place to feed.
But the best wildlife observations were on the short sandy trail preparing to leave the river. A black shiny Pompilid wasp was energetically dragging a paralyzed (grass?) spider nearly as large as the wasp. The wasp dropped the spider and flew off 10-15 feet when I approached; but then in about 3-5 minutes it returned to pick it up and continue dragging, all the while nervously and almost continuously flicking its wings. Remarkably, when it reached a deep pool maybe six or seven meters long and 1-2 m wide, filled with schools of large minnows, it gathered the spider up and flew/ swam across/on the suface of the pool for a full munute, carrying the spider to the dense stand of Arundo cane on the other side where I could not visually continue to follow it.
A few m. further along the trail a fence lizard scuttled off to the edge of the Arundo cane and sat there cooperatively for several minutes for me to observe. (I found my binocs focus to about 3 m.) As I stood, a small bright orange and black Phyciodes crescent butterfly came flitting by and stopped to bask in the sun near my feet.. although why it wanted to be any hotter on this day was not clear to me. At 8:30 it was probably 82 air temp. Finally as a parting gift, a Myzinum tiphiid wasp crawled out onto the cool shaded sand and groomed herself or sat quietly. I wondered if she was waiting to detect some sign of the scarab grubs in the sand below.
Best morning walk along the Canadian I've enjoyed this year.
