City Creek Nature Notes – Salt Lake City

May 18, 2017

May 15th

Peregrine Falcon

5:00 p.m. Under an overcast sky, the first mile of canyon forest is nearly at full leaf-out. Temperatures have dropped by ten to fifteen degrees overnight, and thus, there are no butterflies along the road except for one. About ten Rocky Mountain duskywings (Erynnis telemachus) are found alone and in pairs feeding on a white-flowering roadside weed. They are forever frenetic; they never seem to stop moving despite the cold and light breeze. Near mile 0.6, a new unidentified purple orchid has bloomed. It looks like Purple milkvetch, but its leaves are more ovate and the plant rises like a small rose bush, instead of hugging the ground. There is only one plant in the lower canyon. A Sticky Wild Geranium (Geranium viscosissimum), also deep purple in color, blooms from the disturbed ground of a steep roadbank and sheltered in shade. Small blossoms of another purple flower, Houndstongue (Cynoglossum officinale), have opened at several sites along the first mile road. The Houndstongue blossom has a two-toned flower: a lighter purple-pink surrounds inner dark purple petals.

On the road, two three-to-four inch Blue-eyed darner dragonflies (Rhionaeschna multicolor) are grounded by the cold. One has found a patch of sun and warms itself. But these “blue-eyed” darners are not blue. They have the distinctive blue, brown and black geometric pattern of Blue-eyed darner abdomens, but their heads are black, not blue. The first small, biting mosquitoes have risen, probably the common Western Encephalitis mosquito (Culex tarsalis), and a small trickle of blood runs down my leg from the feeding of an unseen assailant. Others land on my arms and neck, but forewarned of their presence, they are unsuccessful.

Song birds have again divided into two main groups. The first is near Guardhouse Gate and the second resides in Pleasant Valley. I count about ten calls in each group. At Pleasant Valley, again about 8 unidentified raptors are soaring above the eastern ridge line and quickly disappear on their flight over the valley. In the spring, these flocks can also be seen crossing over the Avenues, often after a storm front passes through.

Coming back down the Pipeline Trail another hummingbird is heard hidden in the green tube. Near Shark Fin Rock at mile 0.5, a Peregrine falcon is driving a Red-tailed hawk out of the canyon. From the higher Pipeline Trail, I can watch the conflict unfold from an equal or higher altitude than the hawk. The Red-tailed hawk is injured, and it is missing to large trailing feathers on its right wing. The hawk has probably found the peregrine’s nest in the cliffs, and the smaller raptor seeks to deter it from returning. The Red-tail flies straight down canyon, and the determined peregrine flaps furiously about one-hundred feet above it. Then the peregrine turns into a bullet shape and stoops directly at the hawk. At the last second, the hawk rotates on its side and extends its talons. The peregrine open its wings to break its dive and extends its own sharp fingers. The two briefly touch finger tips. How the hawk sees the peregrine is a mystery because the stoop began slightly from behind the larger bird. The attack makes the larger hawk to turn into a circular flight pattern, holding at about 100 feet above the ground. The peregrine stoops again, and again, driving the hawk lower. Finally, the Red-trial disappears into the maples on the far side of the canyon. The peregrine circles above for a three or four turns and then flies off, back up the canyon. I am honored to have witnessed the skirmish.

Although I have never seen a peregrine take a small bird or mallard in the canyon, they do frequently catch mice in Pleasant Valley. Baker describes their feeding on mice as mere “morsels” that supplement their real diet of larger birds. I suspect that the peregrines only nest here, and fly over the ridge to feed on the gigantic bird populations in the marshes of the Great Salt Lake. For many years, a peregrine pair had a nest on the top of one of the grand old hotels in downtown Salt Lake City. There, they fed on plentiful flocks of city pigeons, and an artificial nest equipped with a popular web camera was constructed. Pairs returned to the site until the exterior of the building was renovated in 2010. Next they moved to artificial cliffs in an abandoned quarry along the western-facing slope of the canyon (Monson 2017). In 2016, I watched them raise two young in an abandoned hawk nest near mile 1.1. This year, they have a nest somewhere else in the canyon, not yet located. The Utah peregrines have returned from the abyss.

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Historically, there have been between 20 and 30 nesting peregrine falcons in Utah (Porter and White 1973). The Utah peregrines favor cliff nesting sites similar to the City Creek canyon walls that surround west and upper east sides in the first road mile (id.) Through 1973, the number of breeding peregrines in Utah dropped to two or three pairs, and this was consistent with a world-wide decline in peregrine populations. In 1970, the United States Fish and Wildlife Service place the peregrines on the endangered species list. The United States Environmental Protection Agency banned the use of DDT in 1972. Although the corresponding national decline is presently universally accepted as being caused by DDT as presented in Rachel Carson’s 1963 Silent Spring, but in 1973, Porter and White were hesitant to attribute pesticides as the cause in Utah, even though they found that “[b]etween 1947 and 1961 many thousands of pounds of DDT were deposited . . . directly on the marshes and waters in the Great Salt Lake Valley where nesting peregrines obtained much of their food” (p. 47). Following the ban, their population has recovered worldwide, and in 1999, Fish and Wildlife Service removed the peregrine from the endangered species list. In April 2017, Monson at Brigham Young University published an updated inventory of Utah pergerine falcon nests (Monson 2017), and he found 45 peregrine nesting sites in northern Utah (p. 34). The peregrine’s range also expanded from their 1973 boundaries along the east side of the Great Salt Lake down to Utah Lake. They now are found on the western shore of the Great Salt Lake, east into Summit County, and south to the southern end of Utah County.

In a remarkably poetic book, The Peregrine, British draftsman and amateur naturalist John Alec Baker, followed peregrine falcons from October to April, 1967 near his west English home about 10 miles from the coast (Baker 1967). Peregrines who breed further north overwinter on the warmer English coast. Every two or three days he made a detailed diary entry on their behavior, motivated in part on the then perception that peregrines would go extinct in the next decade. He described the peregrines as ranchers of the sky, who like their earth-bound human counterparts, herd and manage the populations of the many birds including pigeons and ducks.

Peregrines of the Wasatch Front Mountain Range stretching for two hundred miles from Tremonton in the north to Nephi in the south have organized themselves into approximately 10 mile long territories (Monson 2017, Porter and White 1973) as suggested by Baker’s English observation. This year, one of their nests is either in the canyon or on the western slope of with western ridgeline facing the Great Salt Lake marshlands near Farmington.

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On May 15th, 2010, the Salt Lake Tribune recommends the hike to the Radio Towers on the west ridgeline of City Creek Canyon (Salt Lake Tribune).


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