Category Archives: Water and Shore

What’s Wrong With Panther Hollow Lake?

Schenley Park, Water and Shore
Panther Hollow Lake covered in duckweed, 4 July 2025 (photo by Kate St. John)

6 July 2025

If you’ve been to Schenley Park’s Panther Hollow Lake on any hot summer day in the past decade you’ve seen its surface covered in bright green soup and lumpy, slimy pond scum.

Look closely at the green soup and you’ll see that it’s duckweed (Lemnoideae), a floating plant made up of tiny leaf-like structures, each dangling a tiny root.

Duckweed closeup from Panther Hollow lake, Schenley Park, 22 June 2025 (photo by Kate St. John)

The lumpy scum is filamentous algae made up of single cells in long threads. It grows on the bottom of the pond, eventually clumps together and floats to the surface. It smells bad in the heat. Yes, it’s nickname is “pond scum.”

Filamentous algae partially covers Panther Hollow Lake, 4 July 2025 (photo by Kate St. John)

In small amounts native duckweed and algae are beneficial. Duckweed is food for ducks and wildlife. Algae, when it decomposes, is food for invertebrates. Both provide hiding habitat for underwater wildlife.

But in sunny heat these two organisms grow enormously, cover the surface and then …

Algae and duckweed produce oxygen as a by-product of photosynthesis. This is vital for aquatic creatures. At night or when sunlight is not available, however, the plants consume oxygen. In certain cases, the amount of oxygen being used can exceed the amount being produced, and thus results in oxygen depletion and fish kills. This often happens during hot summer months, when the water is warmer and unable to hold greater amounts of oxygen, or on cloudy days, when there is minimal sun. 

— Brandywine Conservancy: Algae & Duckweed: The Costs and Benefits

In late June’s excessive heat Panther Hollow Lake suffered the cost. I was out of town when Andy Georgeson sent me this message and two photos of a fish kill in progress.

[At Panther Hollow Lake on 25 June 2025] I noticed a difference, even from Monday, when I was last there to today. The fish look like they’re really struggling and close to dying.  They were all crowded near the shore that was closer to the train tracks and seemed to be gasping for air with very little movement.

— email from Dr. Andy Georgeson, 25 June 2025
Fish kill at Panther Hollow Lake, 25 June 2025 (photo by Andy Georgeson)
Fish kill at Panther Hollow Lake, 25 June 2025 (photo by Andy Georgeson)
Fish appear to be bluegill, pumpkinseed and 1 catfish (black)

By the time I visited on Wednesday 2 July, the Department of Public Works had removed the dead fish. I found many live fish — more than usual — in the inflow near the cattails.

Lots of fish near the cattails, 2 July 2025 (photo by Kate St. John)

In addition, in this photo I counted 9 circles on the bottom of the pond. Were they made by fish for egg laying? Spawning?

Fish and fish circles near the cattails, 2 July 2025 (photo by Kate St. John)

Children played by Panther Hollow Lake on Wednesday using long sticks to pull the filamentous algae out of the water and set it on the concrete edge.

Children at Panther Hollow Lake using long sticks to remove the algae clumps, 2 July 2025 (photo by Kate St. John)

The Underlying Cause: Panther Hollow Lake has summer algae blooms because it is shallow and has an unnatural concrete edge that allows lots of runoff. Brandywine Conservancy’s #1 solution is to stop nutrients and sediment from running into the lake by:

  • Limiting fertilizer use. (Fertilizer is not happening near Panther Hollow Lake anyway.)
  • Establishing healthy vegetative buffers especially, shrubs, native grasses and wildflowers, to catch and filter runoff. i.e. Remove the concrete edge.

Meanwhile Panther Hollow Lake is eutrophic because it is “old” in the normal life cycle of a lake. Read more at NHLakes: The Life of a Lake.

diagram from The Life of a Lake at NHLakes.org

p.s. A Tip of the Hat to Brandywine Conservancy’s great article on Algae & Duckweed: The Costs and Benefits.

Mrs. Mallard Nests in the Front Yard

Nesting & Courtship, Water and Shore
Mrs. Mallard leads her ducklings away from the nest, Spring 2025 (photo by Caroline Muller)

30 June 2025

This spring my mother’s next door neighbor discovered a mallard nesting in her front yard under the shrubs that line her home’s foundation. It seemed like an unsafe place but Mrs. Mallard had her reasons.

Nesting mallards must be alert for a wide variety of predators including raptors, snakes, weasels, red foxes and raccoons. You would think they’d also avoid humans but our constant presence keeps many of those predators away. That was the calculation Mrs. Mallard made and she was right.

One day a black rate snake approached the nest but the neighbors went on high alert and saved the day. Caroline, who took these photos, drove away the snake with a technique so successful that the snake never came back.

Black rat snake that wanted to raid the nest — failed (photo by Caroline Muller)

One day after they hatched, Mrs. Mallard led her “kids” down the street to the nearest water. Her protectors wished them all a fond farewell.

Seen This Week: Flowers and Crab Tracks

Fish, Frogs, Plants & Fungi, Schenley Park, Water and Shore
Chickory with an insect at “2 o’clock”, Schenley Park, 22 June 2025 (photo by Kate St. John)

28 June 2025

This week was so hot that I barely went outside.

On 22 June the temperature was still pleasant before 10am when I lead an outing in Schenley Park. There were just two of us to see …

  • Chicory with an insect flying in (at 2 o’clock on flower face).
  • Fleabane with a lady beetle.
  • Duckweed in Panther Hollow lake.
Fleabane with a lady beetle, Schenley Park, 22 June 2025 (photo by Kate St. John)
Duckweed from Panther Hollow lake, Schenley Park, 22 June 2025 (photo by Kate St. John)

We visited my mother in Virginia Beach this week. On Thursday I went to look at the water and only stayed half an hour. It was SO HOT!!

At was high tide on the bayside beach at First Landing State Park the news said the air was over 94° and the water 80°. Few people were out.

High tide at the bayside, First Landing State Park, Virginia Beach, 26 June 2025 (photo by Kate St. John)

I found some crab tracks. And then I went back indoors.

Crab tracks on the bayside sand, First Landing State Park, Virginia Beach, 26 June 2025 (photo by Kate St. John)

I’m glad the heat broke at last.

Another Rarity: Beautiful Black Tern Stays Four Days

Water and Shore
Black tern at Imperial Main Pond, 1 June 2025 (photo by Steve Gosser)

5 June 2025

Spring migration in Pittsburgh has been unusual this year. In Allegheny County at least four rare birds have stopped by on their way north.

Black terns (Chlidonias niger) are gorgeous in breeding plumage with a black head and underparts and gray-white back and wings. In flight the bird is mesmerizing while it hunts over water for insects and fish or circles up to view the landscape. At any moment it changes its flight style to resemble a butterfly, a swallow, a nighthawk, a flycatcher or a tern.

Black tern at Imperial Main Pond, 1 June 2025 (photo by Steve Gosser)

These videos are not from Imperial but they show why black terns are so beautiful in flight.

video embedded from BirdWatchingSamsung on YouTube
video embedded from Scott Ramos on YouTube

During its brief stay in Allegheny County over 50 eBirders stopped by to see the black tern and many took photos.

Those embedded below from Macauley Library (Ezra White, Rob Hooten, John Drake, Phillip Rogers) show a sequence of black tern behavior as the bird catches a fish: hovering, diving, coming up with a fish, flying away, resting on the grass.

Black Tern Hunting Sequence, Catching a Fish at Imperial Main Pond

This black tern was the best I’ve ever seen, closer than all the others plus he stood on the ground for a while (a first for me).

Black tern at Imperial Main Pond (photo by Charity Kheshgi)

He also had something to say…

Black Tern Vocalizing at Dusk

Because Allegheny County only sees black terns in migration it will probably be many years before another comes again.

Black tern range: blue=non-breeding, yellow=migration, orange=breeding (map from Wikimedia Commons)

We were lucky it visited in spring when it was beautiful. Black terns are not black in autumn as shown in non-breeding plumage in Ohio, September 2014.

Black tern on fall migration, Sept 2014, Bethel, OH (photo from Wikimedia Commons)

Indeed the bird was beautiful last weekend in Pittsburgh.

Cuttlefish Communicate With Gestures. Is it Sign Language?

Water and Shore
Young cuttlefish with arms up (photo from Wikimedia Commons)

13 May 2025

Cuttlefish are solitary creatures so researchers were surprised to discover that the animals routinely use complex arm gestures when they see another cuttlefish.

Sometimes they’d raise a pair of arms, almost as if waving, which the team dubbed the “up” sign. At other times, the animals swept all their arms to one side (“side”), folded them beneath their heads (“roll”), and touched just the tips of them together (“crown”).

— Science Magazine: Watch cuttlefish communicate—with enthusiastic gestures

To confirm that common cuttlefish (Sepia officinalis) keyed on each other’s gestures, researchers played videos of a gesturing animal to one in the tank. The tank cuttlefish responded with more gestures, not merely mimicking (mirroring) the video.

The gestures generate sound/pressure waves that cuttlefish respond to even when they can’t see the animal who is gesturing:

The scientists observed the cuttlefish “signing” this way when they couldn’t see each other, so they used a hydrophone to capture the pressure waves produced from each sign. When the researchers then played back this sound for the animals without any visual cues, the cuttlefish often responded by signing—particularly right by the hydrophone, the researchers noted to Live Science.

— Science Magazine: Watch cuttlefish communicate—with enthusiastic gestures

See gesturing cuttlefish respond to these cues in the video below. (If the narration is difficult to understand, turn down the sound and read the text.)

video embedded from ScienceAlert External Sources on YouTube

The next step will be to figure out if this is cuttlefish sign language.

Read more at Science Magazine: Watch cuttlefish communicate—with enthusiastic gestures.

For a deeper dive into the intelligence of cuttlefish see this 10-minute video about delayed gratification. It includes cute kids doing a similar delayed gratification experiment + speculation on why cuttlefish can wait for prey to become available.

video embedded from NOVA PBS on YouTube

The Kittiwake Hotel

Bird Behavior, Nesting & Courtship, Water and Shore
Black-legged kittiwake at Svalbard, Norway (photo from Wikimedia Commons)

9 May 2025

Black-legged kittiwakes (Rissa tridactyla) are small members of the gull family that nest communally on sea cliffs.

Black-legged kittiwake sea cliff colony in Seward, AK (photo from Wikimedia Commons)

They are also happy to nest near humans as they do Lowestoft Telephone Exchange building in the UK.

At Kiberg, Norway a building’s exterior was refurbished to house kittiwake nests. As of 25 March this year, the Kittiwake Hotel was fully booked.

Kiberg has a human population of about 200 people.

View of Kiberg, Norway (photo from Wikimedia Commons)

It seems there are more kittiwakes in Kiberg than there are humans. 🙂

*A NOTE ON NAMES: In Europe these birds are simply called “kittiwakes” but North America there are two species: black-legged and red-legged kittiwakes.

Lady Mallards Are on Eggs

Nesting & Courtship, Water and Shore
Female mallard (photo from Wikimedia Commons)

6 May 2025

When I stopped by Duck Hollow early this week I was amazed to see so few mallards and all of them male when only a month ago I saw many more ducks and both sexes. The difference now is that female mallards are on eggs. The males have nothing to do. They never incubate and they don’t help raise the kids.

Last month each female mallard chose a nest site under overhanging vegetation, typically on the ground and typically near water, where she laid a clutch of 1-13 eggs. She incubates the eggs for about 28 days and when she reappears she’ll have ducklings in tow. At night she will brood them until they’re two weeks old.

LINKED female mallard nests in urban planter (photo from Wikimedia Commons)

Urban mallards behave differently than wild mallards. Here are some interesting facts, paraphrased from Birds of the World:

  • Experimental evidence has shown that mallards may be able to assess mammalian predator risk by detecting the animals’ urine at potential nest sites.
  • Urban mallards sometimes nest on woodpiles, on buildings, and on artificial structures such as docks and boats. Not the female in a planter shown above.
  • Unlike wild mallards, urban mallards will re-nest if the first clutch is destroyed or if all chicks are lost to predation. They even raise second broods if they are in unnaturally crowded populations. (*So this is a puzzle: They are overcrowded yet they raise a second brood anyway. Why?)
  • It is rare for a female to abandon her nest during incubation but is common under crowding and in urban populations. (Crowding makes them crazy?)

In the coming weeks mallard eggs will hatch and families will appear on the water. Watch for scenes like this at the end of May.

Female mallard with ducklings (photo from Wikimedia Commons)

Green Heron Has a Bad Hair Day

Bird Behavior, Water and Shore
Green heron with head feathers standing up (photo from Wikimedia Commons)

1 May 2025

Green herons returned to southwestern Pennsylvania last month to hunt our waterways for fish and crustaceans. When life is calm for a green heron — which is most of the time — he keeps his head feathers sleeked.

Green heron at Prospect Park, Brooklyn, NY (photo from Wikimedia Commons)

But when he feels threatened or he wants to threaten someone else, he raises his head feathers, squawks or clucks, and often tail-flips before he rushes his opponent. The further out he stretches his neck, the more upset he is.

video embedded from Wild Florida on YouTube

In this video you can see him tail-flipping.

video embedded from Wild Florida on YouTube

Watch out when green herons have a bad hair day!

Seen This Week: Flooded Mon River, Redbuds and Rain

Schenley Park, Water and Shore, Weather & Sky
Redbud blooming on Clyde Street, 8 April 2025 (photo by Kate St. John)

12 April 2025

A week ago it rained and rained. All that water had to go somewhere and by Monday I could tell it had made it to the Monongahela River at Duck Hollow.

The mud bar at the mouth of Nine Mile Run was covered with fast moving water. A mallard barely had to paddle as he zoomed by.

Monongahela River running high, 7 April 2025 (video by Kate St. John)

Leafout continued with these box elder leaves at Herr’s Island on 9 April. Notice that they have the same 3-leaf arrangement as poison ivy but their shape indicates they are box elder.

Box elder leafing out at Herr’s Island, 9 April 2025 (photo by Kate St. John)

If it wasn’t raining it drizzled for most of the week. On Wednesday 9 April, rain and drizzle kept these tulips closed …

Tulips closed against the rain, 10 April 2025 (photo by Kate St. John)

… and the dusk-like conditions prompted seven deer to graze in full view behind Frick Fine Arts. These two didn’t care that I was looking at them. The other five crossed the driveway and melted down the hillside edge.

2 of 7 deer behind Frick Fine Arts, 10 April 2025 (photo by Kate St. John)

p.s. If all seven are pregnant does we can expect the herd to number 14-21 deer by the end of May.

Miniature Canada Goose? Or Something Else?

Musings & News, Water and Shore
Miniature Canada goose? Comparison of cackling goose to Canada goose (photo from US Fish and Wildlife, Northeast Region)

8 April 2025

I try very hard not to be gullible but sometimes I get taken in. Yesterday was a lesson in Do Not Believe Everything You See On The Internet even if you trust the source. I’m bringing this up today so you, too, can learn the truth.

Yesterday I saw an incredible photo of a very tiny goose from Wild Bird Fund, a trusted wildlife rehab agency in New York City and I believed it. Wrong! It was posted on April Fool’s Day. Duh!

The good news is that in looking up dwarf geese I learned that poor nutrition in the gosling phase can stunk the growth of a young Canada goose who then never reaches full size. Here’s the corrected news.

A Canada Goose the Size of a Pigeon?

Now, what about that half-sized goose in the photo at top? Is it a dwarf? No. It’s a different species!

The Cackling Goose was long considered a group of smaller subspecies of the Canada Goose. In 2004, the smallest 4 of the 11 recognized Canada Goose subspecies were split out as the Cackling Goose. Canada and Cackling Geese hybridize in several locations, which can further complicate identification in the field.

— All About Birds: Description of Cackling goose

Cackling geese (Branta hutchinsii) are about the size of mallards, have stubby bills, steeper foreheads and shorter necks. They are a Rare Bird in Pittsburgh though quite common in winter in New Jersey, the Great Plains and California’s Central Valley.

Two cackling geese with a Canada goose (photo from Wikimedia Commons)