City Creek Nature Notes – Salt Lake City

May 13, 2017

May 10th

Flies

Midnight. In the valley, temperatures are in the low sixties, and this means overnight temperature in the canyon is in the fifties. Everything is in place – water, soil, nutrients, leaf, flower, and life – and the great vernal explosion of growth has begun. My pen and typewriter feel inadequate to the task. With the vernal explosion, everything in the canyon is changing so rapidly, and it is possible only to record a fraction of and a general impression of what is occurring.

4:00 p.m. As I exit the car at the parking lot, a Peregrine falcon zips overhead traveling west to due east. As I start up the road, a Red-tailed hawk is soaring overhead, hovering effortlessly and then moving to the west at a few miles an hour. A down canyon wind just balances it needs for lift and forward propulsion. There about thirty bird calling and singing in the first mile. I can hear the songs of the Dark-eyed Junco, a Western tanager, and the Lazuli Bunting. The bunting also makes separate chirping call. All the song birds are unseen and hidden in the forest.

Woody shrubs are the most prominent flowering plants, and along the first road mile simultaneously, Red-ozier dogwood, serviceberry (Amelanchier sp.), and chokecherry (Prunus virginiana) bushes are blossoming. When heated by sunlight, chokecherry blossoms give off an enticing vanilla odor, but it is not produced when the bush is in shade. On a dogwood complex funnel-like inflorescence, a Western honey bee (Apis mellifera) feeds. At Guardhouse Gate and at the Red Bridge, below Horsechestnut inflorescences, waxy seed pods form. River birch leaves have grown to two or three inches and with hot sun, now are covered in a shiny, wax layer. This may be an adaptation to retain water. At picnic site 1, a pretty flowering invasive, the Star-of-Bethlehem (Ornithogalum umbellatum L.), has about ten blossoms close to the ground. This bulb perennial has small white star-shaped petals that surround a green rim and a set of second interior white petals.

There are about twenty recently common butterflies in the first mile: White cabbage; Painted lady; Zerene fritillary (doubtful); Desert Elfin; and, Western tiger swallowtails; and, Spring Azure. Three examples of new unidentified moth appear. Moths are distinguished from butterflies as they rest. Butterflies fold their wings vertically after landing; moths spread their wings horizontally flat. This small one to two inch moth is light brown, but has a rectangular medium dark brown bar above the trailing edge of its wings.

Ants are active on the road: a tiny black species and larger Carpenter ants (Camponotus sp.). One of the tiny black ants crosses the road carrying a transparent fly wing in its mandibles.

Over the last week and again today, I see a small furry brown bee hovering over the road. To my eyes, it is suspiciously off somehow; the “bee” only has two and not four wings. This is the Black-tailed bee fly (Bombylius major). This fly also has a distinctive long-straight proboscis for sipping nectar, and it lays eggs on bee larvae. I am feeling ill and diarrhetic, and today, for the first time in over two decades, I am compelled to run into the bushes to defecate. Bags that I use to pick up dog droppings from the road are used to remove the mess from the watershed. While this in the category of too much personal information, there is a lesson to be learned. Within less than a minute, the waste mound is covered in over seventy-five flies of three different types, but I make no attempt to identify them. Normally, bees are unseen along the canyon roads and trails, except near waste containers or deer dung piles, but today’s accident reveals that there are hundreds of flies hiding in the bushes and leaf litter. They are both pollinators and nature’s important garbage collectors. Although they favor mule deer and my human droppings, they are less quick to visit canine waste piles left along the road. The flies in turn become food for birds. About ten miles to the west at the Great Salt Lake flats, brine flies fuel the Utah portion of the Pacific Flyway of migratory birds. In a month at the Lake, beaches and lake bed flats will covered in brine flies such that the surface appears to move. Birds wade through the living mass, gorging themselves. In the canyon, the flies restrict themselves to the cool forest understory, and hopefully they feed the Lazuli buntings, warblers and other song birds.

While the flies in the marshes and beaches of the Great Salt Lake support millions of birds, the density of flies in the canyon may be too low, and canyon flies can only supplement canyon the birds’ diets. Assuming based on my accidental experience that there is about one fly per square foot to a depth of fifty feet on either side of the stream and that each fly weighs 12 micrograms, then the first mile holds about 6.3 kilograms of flies (0.12 x 2 x 5,280 x 50). If there are about 50 small birds living in the first canyon mile and each weigh about 100 grams (about 3.5 ounces), then the bird’s mass is about 5 kilograms. Flies alone are insufficient to support the small birds’ higher trophic level.

* * * *

A 2010 Tibetan study of the ecological role of flies and beetles quantifies their effectiveness in removing animal waste from prairies. Wu and Sun placed 248 gram patties of yak dung under screens that allowed either flies alone, beetles alone, or flies with beetles in Tibetan alpine meadows for thirty-two days. Over one month, the beetles removed sixty-seven percent (168 grams) of dung and the flies removed fifty-one percent (127 grams) of the waste. Using Black solider flies, similar results have been obtained by farm management scientists who have used the flies to reduce the volume of livestock waste by 42 percent (Diener, Zurbrugg and Tockner 2009). In the canyon, I have anecdotally noticed similar rates of removal of Mule deer scat by flies and beetles.

What ornithologists know about what birds eat comes in part from a remarkable series of studies by F. E. I. Beal of the United States Department of Agriculture from the first half of the twentieth century in which birds were actively killed and then the contents of their stomachs were examined (Beal 1900, 1911, 1915, 1918). For example, ten robins were taken alfalfa fields in Utah, presumably in the valley and in the region of the canyon, and twelve percent of their stomach contents were beetles (Beal 1915, 6). Thoreau also recorded bird stomach contents. Although he would not kill himself, when his neighbors shot local birds, he sometimes examined the contents of their stomachs (e.g. Thoreau, Journal, January 11, 1861). In a more humane era, non-destructive direct observation of feeding habits and bird feces are studied (e.g. White and Stiles 1990).

* * * *

On May 10th, 1910, the City Commission argued over Chief Engineer’s expenditures to study how to increase the city water supply, and the Commission order all work to stop on waterworks improvements in City Creek Canyon (Salt Lake Herald).

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