Category Archives: Water and Shore

Luring Fish With His Cape

Black heron at Marievale Nature Reserve, South Africa (photo from Wikimedia Commons)

A black dome of feathers stands hunched in a marsh in Africa.

Odd as he looks, he’s ignored by the cattle egrets.

Black heron near cattle egrets at Marievale Nature Reserve, South Africa (photo from Wikimedia Commons)

When he raises his head you can see he’s a black heron (Egretta ardesiaca).

Black heron raises his head at Marievale Nature Reserve, South Africa (photo from Wikimedia Commons)

His cape lures the fish to the darkened water and cuts the glare so he can see below. This behavior is called canopy feeding.

Watch him in action in the tweet below.

(photos from Wikimedia Commons; click on the captions to see the originals)

What Do Diving Ducks Hear Underwater?

  • Long-tailed duck (photo by Steve Gosser)

Last summer a University of Delaware study found out what diving ducks can hear underwater. Why is this important? If we know what ducks can hear, we can save their lives.

Long-tailed ducks, common eiders and surf scoters eat crustaceans and mollusks that they pull from the ocean floor. Their populations are in steep decline, in part because hundreds of thousands of them die as bycatch in gillnets.

The diagram below shows a gillnet used for cod fishing in Newfoundland. Though no one fishes for cod anymore, gillnets are still used for other fish where ducks are diving.

Diagram of cod gillnet in Newfoundland, 1882 (image from Wikimedia Commons)
Drawing in the gillnet near Rakovníka (photo from Wikimedia Commons)

Federal fishing laws solved the bycatch problem for dolphins and whales by requiring pingers to warn the mammals away. Fish can’t hear the pingers but dolphins can. Is there a sound that will work for ducks?

University of Delaware grad student Kate McGrew tested long-tailed ducks, common eiders and surf scoters and found out they can hear 1-3 kHz underwater.

Long-tailed ducks can hear 1 to 3 kHz (screenshot from NYTimes ScienceTake video)

Fish cannot hear above 2 kHz so there’s hope for the ducks.

This New York Times ScienceTake video shows how McGew trained the ducks.

Read more in this University of Delaware article: What do ducks hear?

(photos by Steve Gosser and Cris Hamilton)

This Seabird Relies on Algae

Dovekie at Spitzbergen, Svalbard (photo from Wikimedia Commons)

Though this arctic seabird doesn’t eat algae it will starve if marine algae is not abundant. On Throw Back Thursday we’ll learn more with the help of two vintage articles.

About the size of a starling, the dovekie or little auk (Alle alle) breeds on islands in the high arctic including Greenland, Svalbard, and Franz Josef Land. Its population of 16-82 million birds spends the winter in the North Atlantic, occasionally as far south as Cape Hatteras. Learn more with a video in this article: Birds On Ice: Dovekie.

Dovekies eat small invertebrates and fish but the majority of their diet is made up of copepods. A single dovekie eats 60,000 of them per day. Quadrillions(*) fall prey to dovekies during the breeding season. So … What the heck is a copepod?

Copepod (photo from Wikimedia Commons)

Here’s where the algae comes in.

Copepods eat microscopic marine algae called phytoplankton that contain chlorophyll and need sunlight to live and grow. In the high arctic, the summer sun makes phytoplankton bloom, as seen below in the Barents Sea. It takes quadrillions phytoplankton to feed billions of copepods to feed the dovekies.

Phytoplankton bloom in the Barents Sea (photo by NASA from Wikimedia Commons)

Phytoplankton is really tiny, so small that you need an electron microscope to see it. The Barents Sea bloom above is thought to be Emiliana huxleyi, shown below. The disks are made of calcium carbonate which is also the primary component of seashells. The calcium in phytoplankton makes its way up the food chain.

Phytoplankton Emiliana huxleyi, magnified (image from Wikimedia Commons)

Thus if phytoplankton is scarce, copepods are scarce and the dovekies starve. That’s how a seabird relies on algae.

(photos from Wikimedia Commons; click on the captions to see the originals)

(*) How many copepods? Here’s a back of the napkin calculation: Suppose there are 50 million dovekies, each one eating 60,000 copepods/day. Dovekies live in their breeding range for four to six months, so there have to be quadrillions of copepods available during that period. Dovekies aren’t the only animal that eats copepods. The numbers are staggering! (My original calculation had a power-of-10 problem. See Tom Brown’s correction.)

Schenley Park Helps Stop The Flood

These signs announcing the closure of Schenley Park’s Bridle Trail and some tree removals are actually good news. Here’s why.

Pittsburghers are among the 40 million people in the U.S. who use combined sewer systems that carry both rainwater and sewage. Built between the 1860s and 1920s the pipes dumped directly into our rivers until the 1950s when Allegheny County opened a sewage treatment plant. (Fortunately, Pittsburgh has been disinfecting drinking water since 1911.)

By now our sewers are over 100 years old and too small to handle heavy rain. In some places it takes only a 1/4 inch to cause a sewer overflow, sending toilet paper to the rivers. Meanwhile climate change has brought frequent heavy downpours that flood some valleys with sewage, including the neighborhood below Schenley Park.

That neighborhood, called The Run, is located at the base of Four Mile Run’s watershed where all the old sewers converge before reaching the Monongahela River (highlighted in red on the 3D map below).

3D map of Schenley Park and The Run from (notes in red by Kate St. John)

You’ve probably never visited The Run but you’ve seen it’s most famous building from the Parkway East, the onion domes of Andy Warhol’s family church, St. John Chrysostom Byzantine Catholic Church.

St. John Chrysostom Byzantine Catholic Church down in The Run (photo from Wikimedia Commons)

The Run bears the brunt of heavy downpours when the sewers back up into basements and streets. The Greenfield Community Association’s website has video plus photos of a manhole spouting 20 feet under the Parkway bridge.

Sewage floods The Run, 28 Aug 2016 (photo by Justin Macey)

People are sometimes trapped by the floods in The Run. On 28 August 2016 a father and son had to crawl through the sunroof when their car was swamped on Saline Street. Click here for photos of the flood and rescue.

Father and son waiting for rescue, escaped through the sunroof of their flooded car, The Run, 28 Aug 2016 (photo by Justin Macey)

The less rainwater that enters the sewer system the better it is for The Run. Toward that end the Pittsburgh Water and Sewer Authority (PGH2O) is working in Schenley Park for the next several months, building detention swales along Overlook Drive and the Bridle Trail to channel stormwater away from the sewer system.

When the project is done they’ll plant more trees than they removed.

Schenley Park will help stop the flood.

For more information, see Channeling The Energy of Fast Moving Rain

(photos of signs by Kate St. John, photos of flood by Justin Macey, maps from

What Made These Holes?

Pitted shell found at Chesapeake Bay, Virginia Beach, 28 Nov 2019 (photo by Kate St. John)

Last month I found this pitted shell at Chesapeake Bay in Virginia Beach and assumed the holes were made by sand and waves. But that can’t be true. If it was, most shells would look like this. So what happened here?

A Google search of shells with similar holes revealed the likely cause: a boring sponge.

Boring sponges make their homes by boring holes into the calcium carbonate shells and skeletons of animals like scallops, oysters and corals. Using chemicals, they etch into the shell and then mechanically wash away the tiny shell chips, slowly spreading holes within the skeleton or shell and sometimes across its surface. Eventually, these holes and tunnels can kill their host, but the sponge will continue to live there until the entire shell has eroded away.

from Smithsonian Magazine article about boring sponges: Drill Baby Drill

Cliona celata is a common boring sponge that lives on oyster reefs in Chesapeake Bay and around the world. It’s considered a major pest by Bay oyster harvesters. Here’s what it looks like underwater and in two closeups.

Underwater view of Cliona celata in France (photo from Wikimedia Commons)
Boring sponge, Choptank River watershed, Eastern Shore of Maryland (photo from Wikimedia Commons)
Closeup of boring sponge, Choptank River watershed, Maryland (photo from Wikimedia Commons)

Interestingly, a 2013 study of scallops and boring sponges found that the sponges thrive in the warmer more acidic seawater that results from climate change. This spells bad news for oysters, corals and other shells.

In the future we’ll find more shells like this.

Shells on beach at Cayo Costa Island, FL, including one pitted by boring sponge (photo from Wikimedia Commons)

(first photo by Kate St. John, remaining photos from Wikimedia Commons; click on the captions to see the originals)

A Murmuration Of Shorebirds

A murmuration of sandpipers, Washington state, Nov 2018 (screenshot from YouTube video)

When European starlings are frightened by an aerial predator they fly in tight formation in a giant shimmering blob called a murmuration. If you’ve never seen it, check out these two examples: Murmurations in Lorain by Chad+Chris Saladin and Murmuration a 2011 film on Vimeo.

Starlings aren’t the only ones who fly like this. Shorebirds are masters at staying in formation, flying high and low and sweeping between the waves when threatened from above.

In the video below, a shorebird flock flashes black and white at Ocean Shores, Washington in November 2018. Their backs are dark, their bellies are white, so they change color as they turn in the air.

The flock is doing this for a reason.

Watch a predator dive in at the 0:13 time mark. It looks like a peregrine falcon to me. 🙂

(screenshot from video by Peggy Dolane on YouTube)

p.s. Starlings and sandpipers have other similarities. Back in 2008 I mused about starlings as “Land”pipers.

What Swans Do With Their Heads Underwater

This week Britain’s BBO Wildlife Trust shared a glimpse into the underwater world of swans and ducks.

Mute swans have such long necks that they can feed on the bottom while floating on the surface. Ducks have to dive.

While the swan is feeding tufted ducks come and go, their bodies so buoyant that their feet must flap continuously to keep them submerged.

If this had been filmed in North America they would be our own species: tundra swans and ring-necked ducks.

(video from Jack Perks via BBO Wildlife Trust)

Courting Cahows

Pair of Bermuda petrels at Nonsuch Island, Bermuda, 31 Oct 2019 (screenshot from Cornell Labs Bermuda Cahowcam)

November is courtship time for one of the rarest seabirds on earth.

The Bermuda petrel (Pterodroma cahow) or cahow (pronounced ka-HOW) ranges across the Atlantic Ocean, returning to land only once a year to court and breed at Bermuda.

Cahows nest in dark burrows which they access only at night, so secretive that they were presumed extinct until 1951 when the last 17-18 pairs were discovered on an isolated Bermuda island.

Every year the odds are against an egg becoming an adult. However the birds’ long breeding lives, 30-40 years, ensure the species will survive as long as there are safe places to nest — and that’s the rub. Rats were eradicated from their breeding colonies but many of the burrows are on islands threatened by hurricanes and sea level rise.

Since 2001 the Cahow Recovery Program has been setting up safe breeding burrows on Nonsuch Island and translocating a few pre-fledgled birds to the burrows in hopes they will return there to breed when they reach maturity at 3-6 years of age. So far so good. There are now 15 pairs on Nonsuch, two of which use burrows equipped with live streaming Cahow cams under infrared light.

November is the time to watch the cameras at Cornell Lab’s Bermuda Petrel Cams. The pairs return to their burrows, prepare the nest, court and copulate. In the video below a pair touches beaks and preens in the courtship behavior called allopreening.

Watch the Cahow cams this month, especially at night. The birds are most active on the darkest nights of the New Moon.

Cahows leave their burrows in December, then the female returns in January to lay her single egg. If all goes well a chick will fledge in July.

The long process of creating and raising a single cahow chick has just begun.

p.s. Here’s an amazing fact about cahows: Notice that the birds have tube-like noses. These structures take the salt out of saltwater so they can drink it. They sneeze the salt out of their noses. There are more amazing cahow facts here.

(screenshot and video from Cornell Lab’s Bermuda Petrel cams)

My Name Is Halloween

Halloween hermit crab (photo from Wikimedia Commons)

Yesterday’s peregrine news pre-empted this Halloween post, so here it is a day late.

The Halloween hermit crab (Ciliopagurus strigatus) lives in cone-shaped shells on coral, rubble, and rocky reefs in the Indian and Pacific Oceans. Just two inches long, he forages at night on meat, carrion, seaweed and algae. His scavenging behavior makes him a useful cleaner-upper in reef aquariums.

However, watch out! The Halloween hermit crab is belligerent. He will …

  • Fight other hermit crabs for a desirable shell.
  • Steal an occupied shell by yanking a weaker hermit crab out of it. (This means death for the homeless crab.)
  • Trample and ruin flat corals,
  • Steal food from the mouths of large corals,
  • Eat docile bottom-dwelling fish in the aquarium.

If this crab is not fed meat, he eats his neighbors.

Not a compliant pet. Scary!

(photo from Wikimedia Commons; click on the caption to see the original)