The black silhouettes in this tree near the Cathedral of Learning are not leaves. They're crows.
Pittsburgh's crow population has swelled since the weather turned cold last weekend. On Monday I counted 4,000 flying into Oakland from the south, pausing on the roof of Carnegie Museum before heading to their final destination.
I couldn't even see the crows arriving from east, west and north but distant trees at Schenley Farms were coated with crows and hundreds, perhaps thousands, gathered on the rooftops north of Fifth Avenue. My cellphone barely captured a look at them as night was falling.
Where did they roost? I didn't stay long enough to find out, but they left their evidence behind.
On Tuesday Claire Staples sent me photos from St. Paul's Cathedral on Fifth Avenue. The crows left a mess on the wall and sidewalk below the stately London plane trees.
For now the crows are roosting near Fifth Ave and Craig Street but that will change. They're wearing out their welcome.
Tuesday evening (October 23) Michelle Kienholz sent me the photo below of a huge flock of crows flying over Schenley Park toward CMU at 6pm. See those specks above the horizon? Hundreds of them!
Yes, it's late October and the crows are back in Pittsburgh for the winter. This is just the beginning of the flock. More will follow.
In the next few weeks the crows will move their roost several times until they settle on a favorite safe place. Meanwhile, you'll see them at dawn and dusk flying down the Allegheny River valley and through Oakland.
In this video from India, see the house crows (Corvus splendens) use their slotted wings to stay aloft in the strong wind. Someone off camera is tossing bread in the air. The crows hover and flap to catch it.
Slotted wings save energy as the crow flies.
It looks like fun.
p.s. Test your skills at identifying birds in flight. Find a pigeon (or three) that parachutes in to join the flock. How can you tell it's a pigeon? Pigeons have pointed wings.
It doesn't make sense but if your wings are the right shape flapping saves energy.
Birds and airplanes must constantly overcome drag to stay aloft. One source of induced drag occurs during lift when swirls of air, called vortices, roll off the wingtips. This small plane generates a huge wingtip vortex, forcing it to burn more fuel as it flies.
Large soaring birds, such as turkey vultures, reduce drag in two ways. Their wingtip feathers form slots that break the single vortex into smaller ones (small is good!), and they turn their wingtips up as they soar.
Southwest Airlines turns up its wingtips, too, to save fuel.
But what about smaller birds that flap all the time? Are they doomed to inefficient, labor-intensive flight? A new study from Sweden says no.
Biologists at Lund University studied jackdaws (Corvus monedula), a corvid smaller than the American crow. Using mist and multiple cameras they found that the birds' slotted feathers, specifically designed for flapping flight, also break up the vortex into multiple swirls. See them rolling off the wings in the study photo at top.
Now that we know slots are efficient for both flapping and soaring, what prompted their development? The study's authors "propose the hypothesis that slotted wings evolved initially to improve performance in powered (i.e. flapping) flight."
In fact, flapping saves so much energy that author Anders Hedenström suggests, "We could potentially build more efficient drones to fly with active wingbeats. Within a ten-year period, we could see drones which have the morphology of a jackdaw."
"Fool me once, shame on you. Fool me twice, shame on me."
A recent study has found that ravens understand this principle as much as we do. When a human cheats a raven, the bird remembers the experience and refuses to deal with that person in the future.
Common ravens (Corvus corax) are one of the smartest birds on earth. Not only can they solve puzzles, find long cached food, and remember their own complex social structures, but they recognize our faces and understand reciprocity with humans.
To test the ravens' memory of fair play, researchers worked with ravens in an aviary in Austria. The goal was two-fold: (1) Can ravens remember who acted cooperatively or defectively in a single session? and (2) Can ravens who observe an interaction but have no first-hand experience remember who's who and act accordingly?
Before the experiment began the ravens learned to offer bread to a human and receive cheese in return. They love cheese.
The experiment involved one-on-one interactions with women the birds had never met before. A woman faced the raven and held out an empty hand to receive bread while displaying a piece of cheese in her other hand. A "fair" experimenter received the bread, then gave the cheese to the raven. A "deceiver" received the bread but ate the cheese herself.
Cheated ravens were outraged! Every one of them vocalized and hopped around, then ate or hid his remaining bread so the cheater couldn't get to it.
A month later the same experimenters tried the exchange again. The ravens remembered the people who cheated them and refused to deal with them.
Did ravens who observed the cheating behavior avoid the deceivers? Not really, but this doesn't mean they were stupid. We humans do it, too. "She cheated him but she won't cheat me." Hah!
So it comes down to personal experience: Fool me once, shame on you. Fool me twice, shame on me.
Pittsburgh's winter crow flock has moved ... just a little. No longer at Heinz Chapel they've now chosen the London plane trees between Schenley Plaza and Carnegie Library.
In front of the Library the air smells fishy, the sidewalks are blotched, and it's slippery when it rains. When folks figure out they're walking on crow poo their reaction is "Yuk!" and then everyone wants to know, "How many crows are there?"
I don't know. We'll have to count. Easier said than done!
Counting a crow roost is an unexpected challenge. Crows prefer tall well-lit trees where they perch close together all over the top. You can't see them from street level because the streetlights shine in your eyes and obscure them. Sneaky crows.
However, you can see them from above. Peter Bell took this photo from an upper floor at the Chevron Science Center in 2011. As you can see, the crows are well lit and countable. The Cathedral of Learning would be a good vantage point for the Library crows.
Count them 1-by-1? Nope! There are far too many crows and they shuffle around.
To get a good estimate, wait until the crows settle in for the night (after 6:00pm) then count one tree full of crows, count the number of trees, and multiply. Here's how.
1. Pick a typical roost tree and count 10 crows in it, circled below.
2. Assume the 10-crow circle represents the size of 10-crow groups. Count the number of circles that have crows in them. See below. (I made the circles bigger where the crows are sparse.)
3. Multiply the number of circles by 10 to get the number of crows in the tree. In this tree it's 10*23 so my 1-tree estimate is 230.
4. Now count the number of trees with roosting crows. I think there may be 20 to 30 trees full of crows at the Library so ...
5. Multiply the 1-tree count by the number of trees. 20*230 is 4,600 30*230 is 6,900.
Before I did this exercise I guessed there were 4,000 crows at the Library.
Anyone up for a challenge? Want to count crows from the Cathedral of Learning?
What species was the last bird you saw in 2016? Which one was your first of the new year?
Mine were the same species. Black birds in a black sky. American crows. Here's why.
Yesterday was the Pittsburgh Christmas Bird Count. I counted birds in my neighborhood (best bird: red-breasted nuthatch) and gave tips to Schenley Park's counter, Mike Fialkovich, on where to find the best raptors.
By noon, Mike had not seen the eastern screech-owl nor the merlins, and he'd only seen one peregrine at Pitt. Oooo! I carved out some time at dusk to run over to Schenley and have a look. Mike did too, but I didn't know that.
Dusk came early. At 4pm I raced around by car and on foot to find the owl (yes!) the merlins (yes!! two!) and both peregrines (alas, none). Interestingly, Mike and I saw the merlins at the same time but did not see each other.
Meanwhile, I couldn't help but see hundreds of crows coming in to Schenley and Pitt for the night, still flying after sunset. By the time I got home no other birds were out. Crows were my Last Bird of 2016.
This morning before dawn they flew over my house on their way from the roost. American crows were my First Bird of 2017.
Happy New Year!
p.s. When I stepped outdoors to hear the crows, I heard an unexpected Second Bird of 2017: an American robin singing his spring song, Cheerily Cheerio.