Category Archives: Musings & News

96 Million Shade Balls

Early this week YouTube said to me, “Here’s a video you might like.” Maybe you will too.

Crazy as it looks, the Los Angeles Department of Water and Power (LADWP) is happy with the results since they covered their reservoir with 96 million black balls.

LADWP calls them “shade balls” but they used to be called “bird balls.” Yet there’s not a bird in sight. This 12-minute video from Veritasium explains it.

I’ve never seen shade balls in Pittsburgh but I can think of several reasons why:

  • We have much less sun. (fewer sun-induced chemical reactions)
  • Our climate is humid. (less evaporation)
  • Bromates are not the big problem here. (Alas, in Pittsburgh our problem is lead.)

But perhaps I’m missing something. Have you seen shade balls in Pittsburgh? Let me know.

(video from Veritasium on YouTube)

Why So Many Landslides?

After a rainy period or spring thaw in Pittsburgh we inevitably see devastating landslides on the news. Why does Pittsburgh have so many landslides and why are they associated with rain or moisture?

The problem is a combination of a particular bedrock with our steep hillsides. Where both are present the location is landslide prone, as shown on the City of Pittsburgh map below. (Click here to see the City’s interactive landslide-prone map and zoom in for details. Click here for the Allegheny County interactive landslide map.)

Landslide prone areas (screenshot from Pittsburgh GIS Data Download Page)

The house in the video above was inside a landslide zone on Semicir Street overlooking Riverview Park. Add water and … the house collapsed!

The bedrock at fault is Pittsburgh redbed, a claystone that disintegrates into smaller and smaller pieces if exposed to pressure when it’s wet. Redbed is usually under pressure because it’s underneath solid rock and overlying soil. Add water to a steep slope and you have a landslide.

This sandstone boulder on the Bridle Trail in Schenley Park was part of the escarpment above it until the redbed layer beneath it gave way.

An old landslide in Schenley Park on the Bridle Trail, July 2019 (photo by Kate St. John)

Here’s a future landslide on the Lower Panther Hollow Trail. This sandstone boulder, high above my head, will fall some day because the slow drip of water over the boulder has disintegrated the underlying redbed. Notice the reddish crumbled stones.

Sandstone boulder is undercut, a landslide waiting to happen at Lower Panther Hollow Trail, Schenley Park, July 2019 (photo by Kate St. John)

I had read that Pittsburgh redbed disintegrates when wet but I wanted to see for myself so I gathered some redbed rocks and ran an experiment.

Thousands of years ago these small crumbles were a much bigger solid rock but water had already acted on them. Will the crumbles disintegrate in the presence of water and pressure? I kept some rocks dry and soaked others for a day. Here’s my experiment.

Add water and pressure to Pittsburgh redbed claystone and … Watch out below!

p.s. For a really spectacular landslide, check out what happened to Route 30 in East Pittsburgh in April 2018.

(photos and redbed experiment by Kate St. John, house collapse video embedded from WTAE Pittsburgh on YouTube, map from Pittsburgh GIS Data)

Reflect Light, Stay Cool

Nankeen kestrel in Australia (photo from Wikimedia Commons)

How do birds stay cool in hot climates, especially when there’s no shade?

A 2018 Australian study in the journal Nature found that some birds can reflect the hottest part of sunlight, the near infrared (NIR) spectrum.

Near infrared is long-wavelength light beyond the red end of the visible spectrum. Though we can’t see this wavelength we can feel its heat. In fact more than half the sunlight that reaches Earth is in the infrared spectrum, as shown in the graph below.

Most of the sunlight that reaches the Earth’s surface is in the infrared range (simplified image from Wikimedia Commons)

Australia is a good place to study cooling techniques in birds because 70% of the continent is hot, dry and very sunny. The Australian study examined museum specimens of 90 species, classifying them by habitat and testing them for their NIR reflectant properties. Two species stood out.

The nankeen kestrel (Falco cenchroides), named for his yellow color (above), reflects near infrared light from the crown of his head. The azure kingfisher (Ceyx azurea) stays cool by reflecting NIR from his chest. Their feathers can reflect NIR because they have rounder barbs and denser barbules.

Azure kingfisher, Queensland, Australia (featured picture on Wikimedia Commons)

Here’s a graph from the study that compares them with two other species.

Graph of four species (image from Reflectivity article in Nature Communications)

The nankeen kestrel and azure kingfisher are at the top of the NIR reflective scale but low reflectors of visible and UV light. The reverse is true of the blueish bird, a male superb fairywren (Malurus cyaneus). He’s great at reflecting UV and visible light, probably because he lives where it’s moist and shady. The great cormorant (Phalacrocorax carbo) doesn’t reflect much light at all.

Interestingly, near infrared reflectivity is more prevalent in small birds because they benefit more for their size. You can’t tell it from the photo but the azure kingfisher is only as big as a sparrow.

Too hot? Reflect near infrared light to stay cool.

(image credits: nankeen kestrel, sunlight graph and azure kingfisher from Wikimedia Commons. Graph from “Reflection of near-infrared light confers thermal protection in birds” at, Creative Commons license. Click on the captions to see the originals)

That Would Be My Perfect Flight

Falconry birds aren’t pets, they’re partners.

In this short film, Shawn Hayes describes his relationship with birds and how he became a falconer. His co-star in the film is an immature prairie falcon (Falco mexicanus) that he’s working with to orchestrate the perfect flight.

About the bird’s future he says:

The day that I release my bird back out to the wild I know that bird is going to survive. I know that bird is going to go out and probably get a mate and produce other birds in the wild. And I was part of that.

Shawn Hayes, “How One City Man Found His Calling in the Wild”

“Falconry is not a sport, it’s not an art — it’s a way of life.”

(video by Joshua Izenberg on the National Geographic YouTube channel)

What Is Hope’s Legacy?

Terzo and Hope with 2 chicks, 3 eggs, 23 April 2019, 3:35pm (photo from the National Aviary falconcam at Univ of Pittsburgh)

Every year Hope, the mother peregrine at the Cathedral of Learning, kills and eats some of her chicks as they are hatching. Among all the peregrine families on camera this behavior is quite abnormal.

This spring some of you wondered if Hope’s behavior would be passed down to her female offspring. The way to find out is to watch one of her daughters nesting on camera (the behavior cannot be seen otherwise).

Are any of her daughters nesting? Here’s the status of Hope’s fledged offspring:

  1. How many young has Hope fledged during her nesting years so far, 2010-2018? 10 fledglings: 4 at Tarentum Bridge plus 6 at Pitt.
  2. How many of her offspring are banded? 8. (We can only re-identify her young if they are banded.)
  3. Subtract known deaths. Of 8 banded offspring, 3 banded are known dead, 5 banded are presumed alive. (*)
  4. How many of the living are female? 3
  5. How many of her offspring have been reported nesting? NONE
  6. How many of her offspring have been seen anywhere since they left Pittsburgh? NONE

In Hope’s nine years of nesting (2010-2018), she has averaged only 1.1 fledgling per year. None of them has ever been seen again.

By contrast Dorothy, the previous female peregrine at Pitt, averaged 3.0 fledglings per year. (If you don’t count her three elderly unproductive years her average was 3.7.) At least 12 of Dorothy’s kids went on to nest in the Great Lakes region, many on camera. Dorothy has children, grandchildren, great-grands and probably great-great-grands by now. She was a matriarch.

What is Hope’s legacy? So far as we know, nothing. We do know that none of her banded daughters are nesting on camera.

p.s. Hope’s potential of fledglings/year is higher than Dorothy’s. Hope averages 4.25 eggs per year at Pitt; Dorothy averaged 3.93. Hope has fewer fledglings/year because half of her hatchlings do not survive the hatching period.

(photo from the National Aviary falconcam at Univ of Pittsburgh)

(*) Living offspring: We will never know the fate of Hope’s 2 unbanded offspring because we cannot identify them. If they are both alive then Hope has 7 living offspring. Due to the 60% mortality rate among young peregrines, it is statistically likely that Hope has only 4 living offspring from 2010-2018, not 7.

.Details:  Hope: 10 fledgings/8 years = 1.1     Dorothy: 43 fledgings/14 years = 3.0 –or– 41 fledglings/11 years = 3.7

The World In A Water Drop

Spider web at sunrise (photo by Luc Viatour ( via Wikimedia Commons)

If your eyes could focus this closely you’d see that the world through a water drop looks upside down.

Refraction through water also makes rainbows — seen in the spider web above — and optical illusions.

On a chilly damp morning Luc Viatour found a spider web displaying this illusion.

(photo by Luc Viatour ( on Wikimedia Commons. Click on the caption to see the original)

Extinction Capital of the World

  • Kioea. Last seen in 1859.

By now in my series on Hawaii you’ve probably noticed that the rarest birds on the islands are threatened with extinction. Sadly this situation is normal. So many Hawaiian species have gone extinct and so many are on the edge today that Hawaii is known as the Extinction Capital of the World. The group of forest birds called Hawaiian honeycreepers are a case in point.

Five million years ago a flock of finches similar to redpolls (Carpodacus erythrinus) arrived from Asia, flying non-stop for more than 4,000 miles. When they arrived, Oahu and the Big Island didn’t exist, but over millions of years they spread out and evolved into 59 species of Hawaiian honeycreepers with a wide variety of beaks for exploiting Hawaii’s food sources. They diversified more than Darwin’s finches.

Each bird was perfectly evolved to survive Hawaii’s dangers but had no defense against off-island threats. Their exposure came with the arrival of humans. We came in two waves.

Polynesians arrived in Hawaii around 400AD and were here alone for 1,400 years. During that period 30% of the Hawaiian honeycreepers went extinct.

In 1778 Captain James Cook was the first European to see Hawaii, prompting immigration from the rest of the world. Since then, in just 240 years, another 39% of the honeycreepers have gone extinct. 18 species remain but six are so critically endangered they may be gone soon.

The slideshow above shows a fraction of what we’ve lost. The last bird, the black-faced honeycreeper or poo’uli (Melamprosops phaeosoma), is still listed as critically endangered with 1 to 49 individuals left on Earth. However, none have been seen since 26 November 2004. It’s probably gone.

Hawaii’s endemic birds go extinct so easily because of …

  • Habitat loss: Humans cleared the forest for settlements. Some species had such a small range or specialized food that when their patch was gone, they were too.
  • Introduced species, especially rats, cats and mongoose: The birds don’t know to move their nests out of reach.
  • Avian malaria and avian pox: Honeycreepers have no immunity.
  • Mosquitoes: Avian diseases, carried by mosquitoes, arrived with introduced birds. Honeycreepers don’t know to brush mosquitoes away. They catch malaria easily and it kills them.
  • Climate change: There’s safety from mosquitoes at high elevation but climate change is heating the mountains. The mosquitoes are moving uphill.

Avian diseases caught from mosquitoes are the big problem. Fortunately there’s a silver lining. One of the honeycreepers, the Hawai’ian amakihi, can now live with avian malaria and is expanding its range within mosquito territory.

This 27-minute video, made in 2005 by Susanne Clara Bard, tells the story of the Hawai’ian amakihi’s survival. Though this video is a lot longer than I normally post, it’s worth even a short look to learn why Hawaiian birds face so many challenges.

The Hawai’ian amakihi evolved to survive malaria in only 200 years.

(images from Wikimedia Commons; click on the links to see the species account at Wikipedia)

Tour Day 9: Leaving the Big Island of Hawai’i for home

Winning and Losing: Rabbits versus Virus

Invasive rabbit eating invasive rabbit-resistant plant in Australia (photo from Wikimedia Commons)

You would not think that something this cute could be a problem but European rabbits (Oryctolagus cuniculus) have plagued Australia for 160 years. After a century of recurring population explosions (think “plagues of locusts”!) scientists found a virus that kills only European rabbits. They introduced it in 1950 and it worked amazingly well for a while but the rabbit and the virus both evolved. Here’s their story.

Introduced for hunting in Geelong, Australia in 1859, the European rabbit immediately went feral and the population went out of control. Without any predators they covered most of the continent by 1910.

Range of the European rabbit; pink means “Introduced” (map from Wikimedia Commons)

Periodic population explosions, called rabbit plagues, became the norm. The rabbits eat everything. They devastate native plants, push out native animals, denude the countryside and cause dust bowls. In the photo below, at dusk, they are everywhere but probably not a plague yet since there’s still some grass.

So many rabbit holes. No trees or shrubs (photo from Wikimedia Commons)

Hunting and poisoning were ineffective.

Then in 1950 scientists found a virus in South America, called myxoma, that killed European rabbits. They released it in Australia (and in France) and it cut the rabbit population by 99%. Wow!

But a few rabbits lived and so did the virus. Science Magazine reports that “within a decade, rabbit numbers were on the rise again as some evolved resistance to this deadly infection and the virus itself became less deadly.”

This month, a new DNA study of both the rabbit and the virus shows that:

Rabbits on two continents evolved the same genetic changes to beat back the virus—before the virus itself changed and regained the upper hand. […and…] In the 1970s the virus developed a greater ability to suppress the rabbit’s immune responses. That change, as well as the natural emergence of another rabbit-killing virus, has caused populations to decline again.

— Science magazine, 14 February 2019

The arms race continues.

Don’t worry about the rabbits. They had another population explosion in 2004. At last count there are about 200,000,000 of them in Australia.

After all, they breed like rabbits.

For more information, read “Seventy years ago, humans unleashed a killer virus on rabbits. Here’s how they beat it” by Elizabeth Pennisi in Science Magazine.

(photos and range map from Wikimedia Commons. click on the captions to see the originals)