Sinkholes Top the News

Sinkhole in Germany (photo from Wikimedia)

10 December 2024

A sinkhole topped the news in western PA last week when a 64 year old grandmother, Elizabeth Pollard, fell into one after sunset in Unity Twp, Westmoreland County, located 40 miles from Pittsburgh.

Ms. Pollard was last seen Monday [2 December at 5pm] while searching for her cat, Pepper, outside Monday’s Union Restaurant. She fell through the sinkhole that had “just enough dirt” for a roof system and grass to grow, Trooper Limani said.  

Post-Gazette: Crews find body of missing Westmoreland County grandmother at bottom of sinkhole

It took four days to find her body 30 feet down in the Marguerite mine whose roof and pillars are slowly collapsing after it was abandoned in 1950. It’s horrifying to think that when she stepped on a patch of grass a hole opened up and swallowed her. [More news at end.]

Meanwhile an ever-growing sinkhole began in late November in South Wales (news here) and on 4 December the Guardian ran a photo essay of sinkholes around the world.

So I began to wonder: What causes sinkholes? Where are they likely? and Why are they round? My answers will be briefly paraphrased from PA DEP, Wikipedia and USGS.


What causes sinkholes?

Sinkholes are all about water. Water drains rapidly into the ground or runs underground and dissolves or erodes the subsurface, creating a void. For a while the surface remains intact, then it collapses into the void.

Most sinkholes are caused by karst processes – the chemical dissolution of carbonate rocks such as limestone or gypsum.

Human activity can cause sinkholes, too, including:

  • Groundwater pumping
  • Digging, drilling or removing soil
  • Water main breaks and intense concentrations of storm water
  • Dams large and small
  • Mining
  • Heavy loads on the surface.

Where are sinkholes likely?

Naturally occurring: According to American Geosciences, the most sinkhole-prone states are Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania because these have naturally occurring karst beneath the surface. Three kinds of karst are shown on this USGS map.

Natural sinkhole-prone areas, map from USGS

Caused by mines: Mine subsidence is a big problem for abandoned mines in Pennsylvania. As the Post-Gazette points out, sinkholes form when the old mine roof is less than 100 feet below the surface. Nowadays a coal seam just 20 feet below the surface would be strip-mined, not deep mined.

The PA DEP Mine Subsidence Insurance Risk Map shows coal and mine locations. If you live in an undermined area (gray on map), PA DEP says you should get Mine Subsidence Insurance. See the full map here at PA DEP where you can zoom in to your address and get info about insurance.

screenshot of PA DEP Mine Subsidence Insurance Risk Map

Why are sinkholes round?

Wikipedia says sinkholes are usually circular. Gizmodo explains why in “Ask a geologist.”

When a void occurs in sediment that has a certain amount of cohesion (‘stickiness’ among sediment grains), the most stable configuration of the roof of the void is a dome, like the dome of the U.S. Capitol building. If that dome collapses, the vertical sides may remain upright, and the open hole will be circular.

Gizmodo: Why are sinkholes round?

Learn more about the sinkhole tragedy in western PA at:

Learn the warning signs of sinkholes at the 7 Most Common Signs of Sinkholes.

Where’s The Best Place To Find Raccoons?

Raccoon in a tree (photo from Wikimedia Commons)

9 December 2024

If you wanted to find a raccoon, where would you look? Hint: Don’t bother searching in rural areas.

According to the NGS video below, there are 100 times more raccoons in the city than in the country, but we rarely see them. If you live in a city or suburb …

  • Is there a raccoon in your neighborhood?   Definitely
  • … in your yard?   Probably
  • … in your attic or crawl space?   You might be surprised.

Find out about more in this short video from National Geographic.

video embedded from National Geographic on YouTube

Now go check the attic!

p.s. Back in 2008 I watched a family of raccoons nosing around my Greenfield neighborhood. They were aiming for my backyard! Fortunately they never got in the house.

What Are Crows Saying? Listen to the Gaps

Crow cawing (photo by Bennilover via Flickr Creative Commons license)

5 December 2024

Crows are so vocal that we can’t help but think their caws are a language. So what are crows saying in their big boisterous flocks before they roost?

Dr. Douglas Wacker at University of Washington Bothell (UWB) wondered the same thing so in 2017 his team began recording and analyzing pre-roost aggregations on the UWB roofs. The rooftop recordings were not enough to crack the code so now the team has turned to spectrogram analysis.

Dr. Wacker presented information on crow vocalizations at the Olympic Peninsula Audubon Society in November 2024. To measure the calls they analyzed these components.

  • Syllable = a single caw
  • Gap = the length of silence between caws
  • Call = a series of caws
  • Pause = the length of silence between calls
screenshot from Dr. Douglas Wacker presentation to Olympic Peninsula Audubon, Nov 2024

The team recorded crow vocalizations in various contexts and compared the spectrograms. And they discovered an unusual thing. Crows appear to be “saying” things in the silence between their caws (gaps) and the pauses between their calls.

  • Gaps between caws: Are longer in pre-roost aggregations (evening) than in post-roost aggregations (morning).
  • Pauses between calls: Are shorter while mobbing an owl than in pre-roost aggregations.

If you want to know what a crow is saying, listen to their silences.

Crow cawing (photo by Jennifer Aitkens via Flickr Creative Commons license)

Learn more about crow language in this Olympic Peninsula Audubon Society’s video. I have set it to start nearly an hour into the meeting, beginning with spectrogram analysis of crow calls. I’ve included this 15 minute portion here because it is so interesting. Click here to see the entire 1.5 hour meeting.

video embedded from Olympic Peninsula Audubon Society on YouTube. (Starts at 58 mins into the recording)

Some day we might know what this crow is saying. In the meantime, listen to the gaps.

Crow cawing (photo by Jason Hopkins via Flickr Creative Commons license)

p.s. Dr. Wacker described an intriguing idea: The messages in human language come from our sounds. The messages in crow language appear to come from silences. Perhaps we can’t figure out what crows are saying because we aren’t used to listening to the silences.

Seen This Week: Sun and Unexpected Carbon

Early morning sun and fog at Duck Hollow, 25 November 2024 (photo by Kate St. John)

7 December 2024

This week the city received a light dusting of snow but the ground was not as beautiful as the sky. Two examples: Fog and sun at Duck Hollow before Thanksgiving, and a very red sunrise on 4 December.

Sunrise in Pittsburgh, 4 December 2024 (photo by Kate St. John)

What is this? An arrangement of black carbon.

Faulty oven creates black carbon, November 2024 (photo by Kate St. John)

These were the unexpected result of a faulty oven thermostat that carbonized the Thanksgiving biscuits. Fortunately that carbon is only skin deep. My niece cut off the bottoms. The tops were yummy.

It’s Time to Find the Crows!

Crows staging at Schenley Park golf course at sunset on 30 Nov 2024, 4:57pm (photo by Betty Rowland)

6 December 2024

Since late October visiting crows have been pouring into town to join Pittsburgh’s enormous winter crow flock. Their numbers in Shadyside and Oakland grew from 3,600 in mid-October to over 8,000 in mid-November … and then I lost track of them because they moved the roost and changed their flight path.

Alas! The flock is still growing — perhaps to 20,000! — and just three weeks from now on Sat. 28 December will be the annual Pittsburgh Christmas Bird Count (CBC) when we’ll confirm the number of crows that come to town for the winter. If we can find them.

I had hopes last Saturday 30 November when Betty Rowland saw a huge flock staging at Schenley Park’s golf course, photo above. But when Betty checked again on Monday the crows were completely gone.

Our winter crows change or split their roost often in late December because they wear out their welcome so quickly. (See examples here.) So where are they now?

Please help. Let me know where you see lots of crows after sunset or at night in the city and/or Allegheny County. Tell me about …

  • Huge flocks of crows
  • After 4:00pm
  • Where are they?
  • If flying, what direction are they going?

Your sightings are especially important in the week before the CBC, December 22-27.

To get you in the mood, here’s a video from Winter Crow Roost in Lawrence, Massachusetts where they’ve ramped up crow counting with photography and videos. Woo hoo!

video embedded from Winter Crow Roost on YouTube

For more about counting crows in Lawrence, MA see their website at Winter Crow Roost.

Weather Hazards Surround Us

What does 24 inches of snow look like? This is Lake Effect Snow in 2004 (photo from Wikimedia Commons)

5 December 2024

Today’s regional weather map is a bright splash of color, none of it good.

Pittsburgh weather map, 5 Dec 2024, 6am from NWS
  • Blizzard warnings (red) –> add snow 12-20 inches + wind gusts to 60 mph
  • Winter Storm Warnings (pink) –> add snow (but less than 20″) + wind gusts 45-55 mph
  • Lake Effect Snow (green) –> snow bands drop 10-20 inches + wind gusts to 50 mph
  • Gale Warning (pale pink) –> Lake Erie winds 40-60 mph, waves 10-15 feet

All of the forecasted snow is falling on top of existing snow. The photo at top shows 24 inches, though not from this snowstorm.

What do birds do when the weather’s this bad? We found out in November 2014 when a nasty snowstorm hit Buffalo, NY.

It’s a good day to stay home.

Meet Me At The Ledge

Ecco calls from the ledge, 26 Nov 2024 (photo from the National Aviary snapshot camera)

4 December 2024

In just 17 days the winter solstice on 21 December will bring us the shortest day and longest night. Since peregrines cue on the amount of daylight to trigger their breeding season, they aren’t in the mood for courtship right now. But the Pitt peregrines stay at the Cathedral of Learning year round and occasionally visit the nest ledge anyway in the off season. Sometimes they call for their mate to join them in a bowing session.

In the snapshot above Ecco calls for Carla to join him last week. “Hey, Carla. Come here!” She didn’t show up then, but she stopped by on Sunday. However Ecco didn’t arrive. (Note: The sun’s low angle made white dirt-spots glow on the camera housing.)

Carla at the Pitt peregrine nest, 1 Dec 2024 (photo from the National Aviary snapshot camera)

Finally on Monday Ecco and Carla met at the ledge (slideshow from the National Aviary snapshot camera).

Identify Bird Photos With Merlin

Great blue heron at Cuyahoga Valley National Park, 17 March 2021 (photo by Karyn Delaney)

3 December 2024

Did you know you can identify bird photos on your cellphone? Merlin Bird ID’s Photo ID function was updated last month with thousands of images from Macaulay Library, the home of eBird checklist photos, providing more real life photos of birds in context.

Here’s how it works: If you want to identify the photo above, by Karyn Delaney, open the Merlin app (download here) and choose Photo ID as shown in the screenshots below.

Choose a photo on your phone or in your photo library. Make it fill the box.

Merlin wants to know when and were you saw the bird because it helps with bird ID.

Quick results! Plus lots of information about the bird.


I found out about the Photo ID upgrade when the Macaulay Library thanked me for contributing photos to eBird and said they used 3 of them. Since I rarely take pictures of birds I have almost no photos in my eBird checklists. I can almost guess which ones they picked: Two peregrine photos and one mockingbird.

Peregrine at Sewickley Bridge, 28 February 2022 (photo by Kate St. John)
Peregrine at Graff Bridge, Kittanning, 7 Jun 2018 (photo by Kate St. John)
Northern mockingbird missing its tail, Phipps Conservatory front lawn, 27 March 2017 (photo by Kate St. John)

Try out the Merlin app and see how it works.

Add photos to your eBird checklists and contribute to bird identification.

Read more about the Photo ID upgrade here at eBird news.

Always Turn Right

Wild budgerigar flock in Western Australia (photo from Wikimedia Commons)

2 December 2024

How do birds avoid midair collisions? In 2016 scientists learned that budgerigars flying head on toward each other avoid crashes by always turning right.

Wild budgerigars bathing in Karratha, Australia (photo from Wikimedia Commons)

Researchers in Australia trained 14 male budgies to fly in a narrow well lit tunnel, one at a time. After the birds were acclimated they positioned one bird at each end of the tunnel and let them fly straight at each other. Two set of cameras recorded the birds’ reactions.

Over the course of four days, seven budgie pairs made 102 flights with no mishaps. When the researchers reviewed the video, they saw that the birds avoided any aerial mishaps thanks to two evolutionary traits. About 85 percent of the time, the birds turned right upon approach. “This seems to be a simple, efficient and effective strategy for avoiding head-on collisions,” Srinivasan said. 

The budgies also seemed to decide whether to fly over or under an approaching bird, and the pairs rarely made the same choice. … The researchers speculate that either each budgie prefers one flying height over the other, or flock hierarchy determines who flies high and who flies low.

Audubon Magazine: Birds Avoid Mid-Air Collisions By Following These Two Simple Rules

Here’s what the tests looked like.

video embedded from New Scientist on YouTube

We use the same principle in traffic. “Stay on the right.”

Traffic in Yellowstone National Park, July 2014 (photo from Wikimedia Commons)

Well, actually, 70% of the world drives on the right, 30% on the left. Heaven help you when you drive in a country that does the opposite of what you’ve learned!

Fortunately budgies always use the same rule.

Nuthatch Says: I’m Warning You!

White-breasted nuthatch threat display (photo from Wikimedia Commons)

1 December 2024

White-breasted nuthatches (Sitta carolinensis) are small but spunky. When they have a good spot at the feeder they defend it by puffing up.

Sometimes it’s just a mild warning like this tail-fanning to a house sparrow.

White-breasted nuthatch shows a mild warning to an incoming house sparrow (photo from Wikimedia Commons)

Sometimes it’s an open wing display like this one to a tufted titmouse.

White-breasted nuthatch tells tufted titmouse to go away (photo from Wikimedia Commons)

And if it’s really important the nuthatch opens its wings and sways side to side in a mesmerizing display. The bluebird on the other side of this feeder stares for a while and decides not to stick around.

White-breasted nuthatch tells bluebird to go away (video embedded from Birder in VA on YouTube)

I’ve never seen this swaying threat display but I learned about it in BirdNote’s podcast: Nuthatches Sweeping the Nest after they described another unusual nuthatch behavior.

Did you know that white-breasted nuthatches use crushed bugs and other items to lay scent outside the entrance to their nests? Listen to BirdNote to find out more …

… and then watch a nuthatch sweep a bug around its nest hole.

video embedded from Athena Gubbe on YouTube

Now that winter is really here, fill your feeders and wait to see a nuthatch tell the other birds, “I’m warning you!”