All posts by Kate St. John

Not A Nice Flowering Tree

Callery pear gone wild (photo by Richard Gardner,

Yesterday I noticed white flowering trees on the hills and swales near Robinson Town Centre (I-376 West). “How nice,” I thought, “Who planted those trees in the empty places?” No one. They’re invasive.

April is the perfect time to see the invasive extent of callery pears (Pyrus calleryana) because they bloom before our native white-flowering trees: chokecherry, downy serviceberry (shadbush), and hawthorn.

Originally imported from China in the early 1900s as root stock for pear orchards, USDA bred them as landscape trees in the 1950s and came up with a winning cultivar, the thorn-less sterile “Bradford pear.”

From 1960 to the 1990s callery pears were wildly popular as street trees in suburbia. They’re pretty in early spring, colorful in fall, and they grow well in the full sun and disturbed soil found in new subdivisions. The Bradford cultivar is also brittle so commercial plant breeders created other cultivars. That’s when the genie came out of the bottle.

In a single cultivar population the fruits are sterile but if two different cultivars are planted near each other, or even grafted together, insects cross-pollinate them and the trees produce fertile fruit. Birds eat the fruit and disperse the seeds. The trees escape to the wild.

Callery pears grow anywhere. A patch can start with a single tree that becomes a thicket in several years. Dense thickets push out all native species. To make matters worse, the wild trees can have 3-inch thorns! The best field-scale control measure is to brush-hog and then mow every year. They still come up!

Callery pears take over disturbed soil (photo by Britt Slattery, US Fish and Wildlife Service,

Callery pears now grow wild from Texas to New York and Massachusetts. They’re listed as invasive in eight states including our own: Pennsylvania, Maryland, Virginia, South Carolina, Georgia, Alabama, Tennessee, and Illinois.

You’ll see them this month on open hillsides and fields along the interstate, near shopping centers, and at the edges of subdivisions.

Don’t plant callery (Bradford) pears. They are not nice flowering trees.

(photos by Richard Gardner and Britt Slattery via; click on the captions to see the originals)

Schenley Park Outing, Sat. April 20

Redbud about to bloom, 23 April 2018 (photo by Kate St. John)

Spring is here! Let’s get outdoors.

Meet me at the Schenley Park Cafe and Visitor Center for a bird & nature walk in Schenley Park on Saturday, April 20, 8:30a – 10:30a. (Note: Due to scheduling difficulties this walk is on Saturday.)

Trees and wildflower buds are bursting. New birds arrive on every south wind. I’m sure we’ll see redbuds. Will they be open?

Dress for the weather and wear comfortable walking shoes. Don’t forget your binoculars! This event will be held rain or shine, but not in thunder. Check the Events page before you come in case of cancellation.

Hope to see you there!

(photo of a redbud by Kate St. John)

Red Maples Are Complicated

Male red maple flowers fallen from the tree, 10 April 2019 (photo by Kate St. John)

This week the hillsides turned faintly red as red maples (Acer rubrum) bloomed across southwestern Pennsylvania. The city’s maples bloom sooner than the suburbs so I’ve had a preview of what’s to come.

In Schenley Park the ground under some red maples is carpeted with fallen flowers (above) while others retain flowers that are setting seed (below).

Female red maple flowers on the tree, developing samaras, 10 April 2019 (photo by Kate St. John)

That’s because red maples are sexually complicated. They are polygamodioecious which means some trees have only male flowers, some have only female, and some have both (i.e. hermaphroditic). And they can even switch back and forth:

Under the proper conditions, the tree can sometimes switch from male to female, male to hermaphroditic, and hermaphroditic to female.

Wikipedia Acer Rubrum

Watch your local red maples to see what they’re up to. The one in my backyard dropped its flowers a few days ago. This year it’s a male. 😉

p.s. For more on maple phenology, read Chuck Tague’s blog post: Maples In Spring: A Study in Diversity.

(photos by Kate St. John)

Mallard Moms Are On The Nest

Only two weeks ago the mallard flock at Duck Hollow was large and busy with males and females feeding in pairs. Back then the flock was usually 20+ birds but now it’s half that size and mostly male. The females are missing. They’re on the nest.

Female mallards (Anas platyrhynchos) nest on the ground laying one egg per day until the clutch is complete, about 10 eggs.

Though she doesn’t build the nest the mother mallard pulls nearby vegetation toward her body to line the nest bowl. When she begins incubation she plucks down from her breast to surround the eggs and cover them while she’s gone. The eggs hatch in 28 days.

Only the females incubate eggs while the males watch from afar. Except for a recess in early morning and late afternoon, female mallards are hidden all day — if they’ve chosen a good nest site.

In urban settings the ladies choose some creative places, as in the video above and this photo under a stairway in Madison, Wisconsin.

Mallard nesting under a stairway in Madison, Wisconsin (photo from Wikimedia Commons)

Three days before they hatch the mallard chicks call back and forth with their mother from inside the eggs. On hatch day all of them emerge within 6-10 hours. Next morning their mother leads them to water for their first swim. See all of this in Ian Oland’s video, above.

So don’t be surprised when you don’t see female mallards at Duck Hollow in early April. Right now the mother mallards are on the nest.

(video by Ian Oland on YouTube. photo from Wikimedia Commons; click on the caption to see the original)

Why Birds Get Here Last

Map of 1st 2019 ruby-throated hummingbird sightings as of 11 April 2019 from Journey North

This time of year can be frustrating for Pittsburgh birders. Migration is underway and the “good birds” are everywhere but here. Why do we keep missing them? Is there something wrong with us?

It’s not us. It’s where we live. Sometimes the “good birds” get here last.

Ruby-throated hummingbirds are a case in point. Their arrival is tracked every year on the Journey North website (screenshot above) where we can see what we’re missing. In the very warm spring of 2012 they arrived in Ohio and Wisconsin by the end of March but weren’t in most of western Pennsylvania in early April. Hummingbirds surrounded us but they weren’t here yet.

On Throw Back Thursday, see the 2012 maps in this vintage article: Why Birds Get Here Last.

Watch the hummingbirds approach on Journey North’s 2019 first ruby-throated hummingbird map.

p.s. Our definition of a “good bird” is part of our problem. The “good” ones are uncommon so of course they get here last, if at all.

LATER THAT SAME DAY (Thursday April 11, 2019): As if to prove me wrong, birding was exceptionally good today with many new migrants that arrived overnight.

(screenshot of first 2019 ruby-throated hummingbird sightings as of 11 April 2019 from Journey North)

Golden Camouflage

European golden plover in Iceland (photo from Wikimedia Commons)

The world’s three species of golden plovers — European (Pluvialis apricaria), American (P. dominica) and Pacific (P. fulva) — are so stunning in golden breeding plumage that they stand out when we look at them. How do these ground-nesting birds avoid predation when they look so obvious?

They’re wearing golden camouflage.

Above, a European golden plover is easy to see from the side, but blends into the background in the photo below, matching the tundra.

European golden plover blends into the background (photo from Wikimedia Commons)

Speckled golden plumage hides them while they’re incubating. (American golden plover below)

American golden plover matches the ground (photo from Wikimedia Commons)

And their chicks are perfectly camouflaged to match the tundra habitat. Can you find the chick in the photo below?

Who knew that gold can look like moss?

(photos from Wikimedia Commons; click on the captions to see the originals. Embedded tweet from @CrowsAndCompany)

An Acceptable Cliff

Adult peregrine falcon at Presque Isle State park, 2012 (photo by Steve Gosser)

Most of us watch peregrine falcons that nest in cities because that’s where most of us humans spend our time. Inevitably, this leads us to believe that peregrines are city birds that want to be near people, but this isn’t so. What nesting peregrines really want is an inaccessible cliff.

There aren’t many peregrine cliffs in Pennsylvania and none of them are in the western part of the state. All of Pennsylvania’s natural nest sites are steep river cliffs like this one at the Delaware Water Gap.

Delaware Water Gap (photo from Wikimedia Commons)

However, we sometimes create cliffs that are acceptable to peregrines though they look like holes to us. Here’s a rocky cliff that peregrines might use if people weren’t actively digging it. It’s a quartz-porphyry quarry in Germany.

Großsteinberg quarry, Germany (photo from Wikimedia Commons)

Among the many abandoned quarries in the U.K., this old chalk quarry at Greenhithe, Kent looked good to peregrines and they claimed it as their own.

It also looked good to developers who built Bluewater Shopping Centre below the cliffs.

The peregrines don’t mind the mall and the mall’s amenities make it a great place to watch peregrines, as seen in this BBC video from 2013.

For peregrine falcons, an old quarry is an acceptable cliff.

(peregrine photo by Steve Gosser. Remaining photos from Wikimedia Commons; click on the captions to see the originals)

p.s. In 2018 two of Pennsylvania’s 54 peregrine nests were located in quarries, both in the eastern part of the state.

Visualize Bird Song

Screenshot from Bird Song Hero tutorial (Cornell Lab of Ornithology)

Now that the birds are singing again and more singers will arrive on migration, it’s time to practice identifying songs by ear. Yes, it’s hard to do but it’s easier if you can visualize the song.

Just like a sheet of music, a spectrogram of bird song shows how the frequency (pitch) goes up and down. The black dashes graph the frequency and length of the notes. The brown wave graphs loudness in decibels.

Song sparrow spectrogram for Xeno Canto audio XC374118 (audio by Ted Floyd)

Play the matching audio to hear the graph: a song sparrow recorded by Ted Floyd, Xeno Canto XC374118.

This is just one example but you can learn to do it yourself and practice with two quizzes at Cornell Lab’s All About Birds.

  1. Learn how to read the spectrograms that visualize bird song in this video: Bird Song Hero Tutorial.
  2. Two quizzes follow the video or you can try them independently at the Bird Song Hero Challenge. TIP: Watch the sonogram as it plays! Some of them are tricky.

p.s. Did you know that birds sing harmonies we can’t hear? On the song sparrow spectrogram, above, there are tall vertical dashes during the fast part of the song. The bird is harmonizing with himself in the 12,000 HZ frequency. If you’re older than 30-something, you probably can’t hear it.

(screenshot from Bird Song Hero tutorial (Cornell Lab of Ornithology, sonogram and audio from Xeno Canto XC374118 by Ted Floyd)

p.p.s Xeno Canto calls the graphs “sonograms.” It’s an older word for spectrogram. Here’s the difference between “spectrogram” and “sonogram.”

Now Blooming

Hepatica at Cedar Creek Park, 6 April 2019 (photo by Kate St. John)

What’s blooming in southwestern Pennsylvania this weekend?

Yesterday’s joint outing of the Botanical Society of Western PA and Wissahickon Nature Club found a lot of spring flowers at Cedar Creek Park in Westmoreland County, 6 April 2019.

Hepatica was blooming in shades of white, pink and blue. In the photo above, the leaves aren’t visible so I can’t tell if this plant is round-lobed (Anemone americana) or sharp-lobed (Anemone acutiloba) hepatica.

Harbinger of Spring (Erigenia bulbosa) was blooming along the valley trail. Did you know this plant is in the Carrot family?

Harbinger of spring at Cedar Creek Park, 6 April 2019 (photo by Kate St. John)

Snow trillium (Trillium nivale) covered the hillside beyond the last bridge …

Snow trillium at Cedar Creek Park, 6 April 2019 (photo by Kate St. John)

… and spicebush’s (Lindera benzoin) tiny yellow flowers were a nice surprise.

Spicebush at Cedar Creek Park, 6 April 2019 (photo by Kate St. John)

Most of the spring beauty was not in bloom but we found Carolina spring beauty (Claytonia caroliniana), a specialty at Cedar Creek shown below.

Spring Beauty at Cedar Creek Park, 6 April 2019 (photo by Kate St. John)

This bloodroot (Sanguinaria canadensis) was bright white by the bike trail. Its leaves are barely visible, clutching the stem, while a garlic mustard leaf tries to photo-bomb the bottom corner.

Bloodroot at Cedar Creek Park, 6 April 2019 (photo by Kate St. John)

Meanwhile, how are the buckeye buds doing in Schenley Park? Some were unfurling on Friday 5 April 2019. Note the CORRECTION ABOUT BUCKEYES below!

Yellow buckeye buds, starting to unfurl their leaves in Schenley Park, 5 April 2019 (photo by Kate St. John)

CORRECTION ABOUT BUCKEYES: Last week Stephen Tirone investigated the buckeye buds in Schenley and Frick Parks and learned that these are yellow buckeyes (Aesculus flava) not Ohio buckeyes (Aesculus glabra). Though Ohio buckeyes are more common in the wild, Pittsburgh’s parks are not “wild.” Schenley and Frick Parks were landscaped with ornamentals when the parks were established more than 100 years ago. Yellow buckeyes are often planted as ornamental trees and may be hybridized to produce showy flowers. So, yes, these are yellow buckeyes.

(photos by Kate St. John)

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)