Seen This Week: The Duckweed Flood

Schenley Park
When Panther Hollow Lake overflowed on 20 Aug duckweed floated with it, 21 Aug 2026 (photo by Kate St. John)

23 August 2026

On Thursday 20 August, in 45 minutes from 8:10 and 8:55am, it rained 1.55″ at the Allegheny County Airport. For almost 15 minutes it came down at the rate of 3.4″ per hour. Schenley Park’s Panther Hollow Lake was one of many waterways that overflowed. By Friday morning the flood waters had receded, leaving behind a coating of duckweed right up to the high water mark. This was the first time I’ve ever seen a duckweed flood.

Ideally the flood would have been handled by the old concrete overflow channel but it’s blocked by a landslide so the flood ran over the channel edge and down the path to the lake.

An old landslide below the Panther Hollow Bridge blocks Panther Hollow Lake overflow channel, 22 Aug 2026 (photo by Kate St. John)

Water scoured new ditches and carried an old orange cone into the lake. It also beat down the cattails on its way to the duckweed zone.

Flood path to Panther Hollow Lake, 21 Aug 2026 (photo by Kate St. John)

Because Panther Hollow Lake is pond-sized and very shallow it is eutrophic in the summer, covered in duckweed and filamentous algae. On the lake, everything was a sea of green.

Panther Hollow Lake a sea of green, 21 Aug 2026 (photo by Kate St. John)

Duckweed heavily coated the concrete edge, …

Duckweed left behind by the 21 Aug flood, 22 Aug 2026 (photo by Kate St. John)

… and a lumpy log right next to the edge …

Duckweed coating everything from the 21 Aug flood, 22 Aug 2026 (photo by Kate St. John)

… and the grass.

Closeup of duckweed coating grass at the edge of Panther Hollow Lake, 22 Aug 2026 (photo by Kate St. John)

Usually duckweed (Lemnoideae) is a floating plant and each tiny leaf-like structure dangles a tiny root. But the water is gone.

Duckweed from Panther Hollow Lake, 22 June 2025 (photo by Kate St. John)

Will it take another rain storm to wash away the duckweed? Or will the sun desiccate it and make it brown? I’ll have to go back and see.

Another Tick Magnet: Wineberry!

Insects, Spiders, Plants & Fungi
Wineberry, Schenley Park, 5 July 2024 (photo by Kate St. John)

23 August 2026

Ticks have been in the news a lot lately, especially on the East Coast where lone star ticks are causing alpha gal syndrome, an unpleasant and potentially deadly allergy to red meat and (sometimes) dairy products. Just this week The New York Times featured alpha gal, Lyme disease, lone start ticks and black-legged ticks (a.k.a. deer ticks) in The Summer the Ticks Took Over. The news is frightening if this is the first time you’ve ever read about ticks.

Those who spend time in the woods birding, hiking, hunting or foraging are all too aware of the tick hazards in Pennsylvania. We know that Japanese barberry is tick city.

This year there’s news of another tick haven we had not recognized: Wineberry (Rubus phoenicolasius), an Asian member of the Rose family that was introduced to North America in the 1890s as breeding stock for raspberries.

It’s pretty much everywhere and grows well in Pittsburgh’s city parks.

Wineberry, Frick Park, 8 July 2022 (photo by Kate St. John)

It produces tasty berries in July. I’ve eaten them from both Frick and Schenley Parks.

A wineberry berry (photo by Kate St. John)

I should have suspected this dense shrub would be a haven for ticks but I did not think about it until Adam Haritan featured wineberry in a 7-minute video on his YouTube channel Learn Your Land. Check it out.

video embedded from Learn Your Land on YouTube

Evading a Falcon

Bird Behavior, Peregrines, Water and Shore
Rock sandpiper flock over the mudflats of Kachemak Bay, Alaska (photo by Lisa Hupp/USFWS via Wikimedia)

21 August 2026

When migrating shorebirds evade a falcon they form very tight flocks that twist and turn in the air to make the flock look like a solid blob. If they have white bellies and dark backs, the flock changes color as they turn.

When you see these murmurations, look for the falcon who’s chasing them. He’s visible for a split second at approximately 0:46.

video embedded: by Carl Haynie on YouTube

Thanks to a falcon, we witnessed a fantastic murmuration of thousands of dunlins and sanderlings at Griffiths-Priday State Park north of Ocean Shores, WA.

— video caption from Carl Haynie on YouTube

Early Signs That Winter is Coming

Weather & Sky
Western sandpipers in flight (photo from Wikimedia)

19 August 2026

Though the growing season hasn’t ended yet, it is waning fast in Alaska. The Fairbanks area has already lost 5 hours and 45 minutes of sunlight since the June solstice(*) and they’re currently losing nearly 7 minutes of sunlight per day.

The National Weather Service in Fairbanks points out they’ll have less than 14 hours of daylight by September 8 (at 13:49).

Shorebirds key on day length to determine when to migrate. When their very short breeding season ended they gathered at the shore in July and are now on the move in August

Shorebirds assembling at Kinzarof Lagoon, Izembek National Wildlife Refuge in July 2008 (photo from Wikimedia) 

Late August marks the peak departure window for adult arctic-breeding shorebirds leaving Alaska. Species actively migrating out of the state this week include the Western Sandpiper, Dunlin, Lesser Yellowlegs, American Golden-Plover, Buff-breasted Sandpiper, Pectoral Sandpiper, Red Phalarope, and [Hudsonian] Whimbrel.

— Google response to “what shorebirds are migrating out of Alaska this week?

Have we seen any of them in Allegheny County yet? No, but some birds are on the move. Here are screenshots from last night’s BirdCast tracking.

screenshot from BirdCast Migration Dashboard for Allegheny County, PA. Data for the night of 19 August 2026

Notice that we’ve had two exceptional nights this month.

screenshot from BirdCast Migration Dashboard for Allegheny County, PA. Data for the night of 19 August 2026

I missed them because I haven’t been paying attention. It’s already time to gear up for fall migration.

It Only Lasts One Night

Plants & Fungi
Night-blooming cereus (probably Epiphyllum) in my sister’s yard, 17 August 2026, 8:47pm (photo by Kate St. John)

18 August 2026

My sister has a night-blooming cereus plant that produces beautiful flowers with a lovely scent. Each flower lasts only one night. The bud begins to open after sunset, it’s in full bloom around midnight and begins wilting right after that.

Night-blooming cereus is the common name for many night-blooming plants that behave like this. My sister’s plant appears to be an Epiphyllum sp, native to Central and South America.

Last night at 8:45pm the plant was in bud, pictured at top.

After the midnight thunderstorm passed, my sister went out at 1:10am to photograph it in full bloom.

Night-blooming cereus (probably Epiphyllum) in my sister’s yard, 18 August 2026, 1:11am (photo by Mary Mitchell)

This morning it is closed and wilting.

The morning after. Flower is wilting, 18 August 2026, 7:12am (photo by Kate St. John)

If we had the time and equipment to photograph it all night, here’s what it would have looked like.

2019 timelapse video embedded from Kevin Henderson on YouTube

The North Pole is Running Away, But Not as Fast as it Used To

Musings & News
Movement of magnetic North and South poles 1945-2000 (image from Wikimedia)

17 August 2026

Yesterday I described how rock pigeons and rock lobsters navigate using earth’s magnetic field. Behind the scenes I learned how much the magnetic North pole has moved recently. I hadn’t noticed because I no longer use a manual compass that has to be manually adjusted for the local declination.

Suunto Compass (from Suunto Watches)
World Magnetic Map showing declination from true north (from NOAA World Magnetic Model products)

Here’s how the poles have moved in an animation showing 1590 to 2025. Each pole is depicted as a green dot. The red, green and blue lines are magnetic 0° and declinations. The years 1590-1830 were backwards calculated.

NOAA Magnetic Pole Shift 1590-2025, from NCEI Historical Magnetic Declination Viewer, NCEI Geomagnetism interactive map

Notice that the magnetic South pole used to move relatively fast but in the 2000s the magnetic North pole sped up considerably!

By 2019 when this video (below) was created, magnetic north had moved more than 2,300 km (1,430 mi) from northern Canada toward Siberia.

Why Earth’s Magnetic North is Shifting, 2019 (video embedded from Radio Free Europe/Radio Liberty on YouTube)

How fast did it go? Seven years ago it was moving 55km/year (34.17 miles/year) but predicted to slow down.

Magnetic North speed 1900-2019 from Wikimedia

And so it has:

The magnetic north pole is moving at a current speed of about 35-45 km (22-28 mi) per year toward Siberia. Its speed has slowed down recently after peaking at around 55 km (34 mi) per year in the early 2000s.

One last video from 2019, slightly redundant, that also explains how our GPS mapping apps are just fine.

video embedded from CBS 17 Raleigh on YouTube

Our satellites and cellphones make it easy for us. I wonder how the rock pigeons and rock lobsters cope with it.

What Do Rock Pigeons and Rock Lobsters Have in Common?

Bird Behavior, Water and Shore
Caribbean spiny lobster and Rock pigeon (photos from Wikimedia)

16 August 2026

Answer: It’s more than just the word “rock.”

Pigeons are known for their ability to fly home even when dropped off in an unfamiliar location, a feat they are able to accomplish, in part, because they have an internal compass that can see Earth’s magnetic field.

World Magnetic Map showing declination from true north (from NOAA World Magnetic Model products)

Where is the compass inside a pigeon? A study published this spring by the Max Planck Institute of Animal Behavior revealed that pigeons navigate using magnetic sensors in their livers. The study highlights these key points.

  • Previously unknown navigation mechanism: Pigeons may sense the Earth’s magnetic field using iron-rich immune cells in their livers, a quantum effect.
  • Navigation experiments: Removing iron-containing immune cells in the liver disrupted pigeons’ sense of direction under overcast skies when the sun was not visible.
  • Sensing via the immune system: Findings suggest a new link between immunity and sensory perception in birds, and potentially other animal species.
— Pigeons navigate using magnetic sensors in their livers.

Magnetic sensing and navigation is a trait that both rock pigeons and rock lobsters have in common.

Rock lobsters, also known as spiny lobsters, live in crevices and come out at night to eat.

Spiny lobsters are unique among the crustaceans in that they undergo large, coordinated migrations every year. Sometimes in the fall over 50 lobsters will line up in single file and walk along the ocean floor. The tips of each lobster’s long antenna will always be in contact with the lobster in front of it, so that even if the lobster cannot see, it will not lose its place in line. No one knows the reasons for this migration, but it could be in response to changing environmental conditions (i.e. temperature) or to mate or to molt en masse.

— oceanbites.org: Migrating lobsters use magnets to find their way

How are spiny lobsters finding their way?

In 2016 researchers watched how Caribbean spiny lobsters (Panulirus argus) moved in reaction to “north” and “south” magnetic pulses in the lab. The lobsters were spot on for detecting magnetic fields. Read more at Oceanbites.org: Migrating lobsters use magnets to find their way.

What does their migration look like? PBS Nature planted a robot spy-lobster among Caribbean spiny lobsters to track their migration. When the group began to migrate, the spy-lobster followed.

video embedded from Nature on PBS in YouTube

Eventually the real lobsters outpaced the spy-lobster and left him behind.

Rock lobsters know where they’re going.

Seen This Week: Butterflies and Fruits

Insects, Spiders, Plants & Fungi, Trees

photos by Mary DeVaughn

15 August 2026

Seen this week were …

Butterflies:

On Friday morning, 14 August, I got a message from Mary DeVaughn: “Just caught some nice camouflage here! A “dead leaf” landed on my windowsill – but then it opened its wings!” It’s a question mark butterfly (Polygonia interrogationis).

Charity Kheshgi and I noticed the same thing at Frick Park last Sunday when a hackberry emperor (Asterocampa celtis) paused on the cobbled path. My cellphone photos are poor quality but you can see that it’s camouflaged when closed and visible when open.

On 9 August we also found a catalpa sphinx moth caterpillar (Ceratomia catalpae) — a catalpa worm — almost exactly a year since we saw them in Frick in August 2025. Click here to see a better photo of this caterpillar + its host plant + a look at the moth.

Catalpa sphinx moth caterpillar, Frick Park, 9 August 2026 (photo by Kate St. John)

Various fruits seen include …

Flowers and round seed capsules of Indian tobacco (Lobelia inflata).

Indian tobacco flowers and “fruits,” Frick Park, 9 August 2026 (photo by Kate St. John)

Fruits of a native hawthorn tree (Crataegus species). The seeds inside these fruits are mildly toxic to humans.

Hawthorn fruits in Frick Park, 9 August 2026 (photo by Kate St. John)

Fruits of invasive common buckthorn (Rhamnus cathartica). These are toxic to humans and pets but, like the hawthorn, are readily eaten by birds.

Common buckthorn fruits in Frick Park, 9 August 2026 (photo by Kate St. John)

Shorebirds at the Beach

Migration, Water and Shore
Sanderlings at the beach (photo from Wikimedia)

14 August 2026

Going to the beach? You’re certain to see shorebirds but who are they? They may be difficult to identify if they’re not in breeding plumage.

To give you some practice, check out this video by Get to Know Nature. Filmed at the New Jersey shore, it highlights six species. You might not see a piping plover at your beach. They are Near Threatened.

video embedded from Get To Know Nature on YouTube

Good luck and have fun!