Jan 18 2017

How Many Crows Are There?

Published by under Crows & Ravens

Crows in a tree on Thackeray (photo by Peter Bell)

Crows in a tree on Thackeray (photo by Peter Bell)

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.

One group of 10 crows in a tree (photo by Peter Bell, retouched)

One group of 10 crows in a tree (photo by Peter Bell, retouched)


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.)

10-crow areas in a roost tree (photo by Peter Bell, retouched)

10-crow areas in a roost tree (photo by Peter Bell, retouched)

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?

How many crows are there?


(photo by Peter Bell)

p.s. My husband says that if this is too difficult, count the number of crow legs and divide by two. 😉

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Jan 17 2017

The Case of Extinct Birds

Passenger pigeon, Bird Hall at Carnegie Museum (photo by Kate St. John)

Passenger Pigeon taxidermy mount, Bird Hall at Carnegie Museum (photo by Kate St. John)

Because Earth’s current extinction rate is 1,000 times the normal background rate, scientists believe we’re at the start of the sixth mass extinction.

What does extinction look like?   I visited a large display case at Carnegie Museum’s Bird Hall to find out.

In the case of extinct birds, each species has a story. The reason for extinction is often well known but the exact date of disappearance is usually obscure, though there are exceptions.

Take, for instance, the passenger pigeon (Ectopistes migratorius) shown above.  Native to eastern North America, we would have seen passenger pigeons in Pennsylvania if we’d lived 200 years ago but relentless uncontrolled hunting wiped out their population until it crashed.  The last passenger pigeon died in captivity on 1 September 1914 in the Cincinnati Zoo.  Extinction was caused by humans because we liked to eat them.


Guadalupe Storm-Petrel, Bird Hall at Carnegie Museum (photo by Kate St. John)

Guadalupe Storm-Petrel specimen, Bird Hall at Carnegie Museum (photo by Kate St. John)

The Guadalupe storm-petrel (Oceanodroma macrodactyla) disappeared more quietly. Always hard to distinguish from its close relative, Leach’s storm-petrel, this bird nested only on Guadalupe Island off the coast of Mexico’s Baja California. Cats were introduced there in the late 19th century and by 1912 no storm-petrels could be found. According to Wikipedia, “Only old, abandoned burrows and the decayed remains of storm petrels killed by cats were found in the years thereafter.”  Extinction was caused by cats introduced by humans.


Laysan Crake specimen, Bird Hall at Carnegie Museum (photo by Kate St. John)

Laysan Crake (Laysan rail) specimen, Bird Hall at Carnegie Museum (photo by Kate St. John)

The Laysan crake or Laysan rail (Porzana palmeri) couldn’t fly but that didn’t matter because he lived on the remote island of Laysan. Unfortunately his population crashed due to habitat loss when humans introduced rabbits to his island home. The final blow came in 1944 when rats jumped ship onto Laysan.  Extinction was forced by two human-introduced species: rabbits and rats.

There are many stories in the case of extinct birds.  Learn why they disappeared at Carnegie Museum‘s Bird Hall.


(photos by Kate St. John)

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Jan 16 2017

A Year of Drama: Pitt Peregrine Highlights 2016

Published by under Peregrines

Terzo looks; 2nd chick is gone (photo from the National Aviary falconcam at Univ of Pittsburgh)

Terzo looks; 2nd chick is gone (photo from the National Aviary falconcam at Univ of Pittsburgh)

When the female peregrine Hope moved from Tarentum to the Cathedral of Learning, I thought 2016 would be calm and joyful.  Instead it was filled with drama.

Here’s a recap of last year’s Pitt peregrine activity, complete with a slideshow of 2016 highlights.

To see a slideshow of highlights from the year of drama, 2016, click here or on the photo above.


(snapshot from the National Aviary falconcam at the University of Pittsburgh’s Cathedral of Learning)

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Jan 15 2017

Hawks Soaring

Red-tailed hawk soaring (photo by Cris Hamilton)

Red-tailed hawk soaring (photo by Cris Hamilton)

Though they won’t lay eggs until March or April, red-tailed hawks are already thinking ahead in western Pennsylvania.

On sunny days in January, they claim their nesting territory by soaring above their chosen land, a gesture that says “This is mine!”

Red-tailed hawks (Buteo jamaicensis) are generally monogamous and mate for life.  The pairs soar together in courtship flight, the male higher than his lady.  Sometimes both of them dangle their legs or he approaches her from above and touches her with his toes.

After the female zooms to the nest area the male goes into roller coaster mode, steeply flying up and down, ending with his own zoom to the female and then … perhaps they’ll mate.

Watch for soaring hawks today.  The weather promises to be sunny.


(photo by Cris Hamilton)

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Jan 14 2017


Published by under Cranes

Sandhill cranes in western Pennsylvania, 2015 (photo by Steve Gosser)

Sandhill cranes in western Pennsylvania, 2015 (photo by Steve Gosser)

Yesterday five of us traveled north to the Volant Strips in Lawrence County to find a northern shrike and short-eared owls.

What we hadn’t expected was a huge flock of 112 sandhill cranes!  The total rose to 124 when we saw 12 in a later part of our trip.

This wintering flock is the largest I’ve ever seen outside of Nebraska.

In the end, we saw the shrike and two short-eared owls but they couldn’t match the wonder of so many sandhill cranes.  🙂


(photo by Steve Gosser, 2015)

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Jan 13 2017

Don’t Miss This Outing, Jan 22

Published by under Books & Events

African penguin at the National Aviary (photo from Wikimedia Commons)

African penguin at the National Aviary (photo from Wikimedia Commons)

UPDATE, JAN 17: No More Reservations accepted. The tour is full.

You may have missed my announcement about the National Aviary outing on Sunday January 22 — but don’t miss the event!

It’s a private tour. Only $10!  Openings still available.  Sign-up soon!

Click here for details…

Let’s Go To The Aviary, January 22!



(photo from Wikimedia Commons. Click on the image to see the original)

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Jan 12 2017

He Wears His Status On His Chest

Published by under Bird Behavior

Comparing bib size in two male House Sparrows (photos from Wikimedia Commons)

Comparing bib size in two male House Sparrows (photos from Wikimedia Commons)

On Throw Back Thursday:

Who’s in charge among the house sparrows?  The size of the male’s black bib is a clue.  Find out more in this vintage blog from 2011.



(photos from Wikimedia Commons: To see the originals, click here for photo on the left, here for photo on the right)

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Jan 11 2017

Introduced 204 Years Ago

Published by under Plants

Young pineapple on the stem (photo from Wikimedia Commons)

Young pineapple on the stem (photo from Wikimedia Commons)

On this date in 1813 the pineapple was introduced to Hawaii.  No, it’s not a native plant.

Pineapples (Ananas comosus) are bromeliads indigenous to South America from southern Brazil to Paraguay.  Because we like their fruit they’re now cultivated across the world in such far flung places as Costa Rica, the Philippines, Thailand and India.

We also grow pineapples for their beauty.  Here’s a plant with variegated leaves in Parque Nacional del Café in Quindio, Colombia.  It’s in the National Coffee Park.

Pineapple plant with inflorescence, varigated variety (photo from Wikimedia Commons)

Variegated pineapple with inflorescence, Parque Nacional del Café, Quindio, Colombia (photo from Wikimedia Commons)

Ironically, this pineapple is growing on its native continent in a park dedicated to an imported crop.  Coffee is originally from Ethiopia.


(*) The Hawaiian introduction date may have been 1/21 instead of 1/11.  Perhaps poor handwriting in the historical record makes it hard to determine whether it’s “11” or “21.”

(photos from Wikimedia Commons. Click on the images to see the originals)

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Jan 10 2017

How Museums Saved The Peregrine Falcon

Two specimens, Peregrine Falcon egg clutches, anatum subspecies, Carnegie Museum (photo by Steve Rogers)

Two specimens of peregrine falcon egg clutches at Carnegie Museum, collected at Baja California in 1921 (photo by Steve Rogers)

What good is a museum collection of bird eggs?  In the case of peregrine falcons, egg collections helped save the species.

After World War II new organochlorine insecticides were introduced on the open market and widely used in agriculture. Some of them, such as seed dressings of dieldrin, aldrin and heptachlor, instantly killed birds as they fed in the fields.  DDT was more insidious.

By the mid 1960s, seed dressings were already banned in Britain but the peregrine population was still crashing and Derek Ratcliffe wondered if something else was going on.  Since 1951 he and other peregrine monitors had seen many broken eggs in eyries and frequent nest failure.  Ratcliffe wondered if peregrine eggs were collapsing because the eggshells were thin.  He decided to find out.

Egg collections are empty shells (notice the tiny drill hole in each specimen above).  You must not break them to measure the shell’s thickness.  However the weight of the shell correlates to thickness if you account for the size of the egg.  Ratcliffe weighed each egg and measured its length and width.  Then he used this formula to determine its thickness index.

Shell thickness index = Weight of eggshell (mg) / [Length (mm) * Breadth (mm)]

For his preliminary study, Ratcliffe measured egg specimens in the British Museum of Natural History and 30 eggs collected in more recent peregrine surveys.  Indeed the shells had thinned since World War II, prompting further research.

Ratcliffe’s final study, published in 1967, showed that the turning point in Britain was in 1947.  Prior to that shell thickness averaged a steady 1.82 for over 125 years.  After 1947 the thickness dropped to 1.53, an average loss of 16%.  (Later studies showed trace amounts of DDE in the shells.)

Meanwhile, Hickey and Anderson at the University of Wisconsin wondered if eggshells were thinning in North America, too.  Their 1968 study measured eggshells of 13 raptors and 9 fish-eating birds and found that, yes, peregrine falcons were affected by DDT in the U.S.

Peregrine populations were crashing on two continents because of overwhelming nest failure in the face of DDT.  Political and legislative wheels turned slowly.  DDT was banned in the U.S. in 1972. Then the peregrine falcon recovery began.  By 1999 peregrines were doing so well in the western U.S. that they were taken off the U.S. Endangered Species List.

Museum egg collections played a key role in this happy result.  It’s not a stretch to say that museums helped save the peregrine falcon.


(photo by Steve Rogers from the Section of Birds at Carnegie Museum of Natural History)

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Jan 09 2017

Let’s Go To The Aviary, January 22!

Published by under Books & Events

Hyacinth macaw at the National Aviary in Pittsburgh (photo by Christopher Westfield via Wikimedia Commons)
UPDATE, JAN 17: No More Reservations accepted. The tour is full.

Let’s go birding indoors!

Join me for a guided tour of the National Aviary with Aviary docent (and Falconuts founder) John English.

When:  Sunday January 22, 10:00am to noon. Stay longer if you wish and browse on your own.

Where: The National Aviary
700 Arch Street, Pittsburgh, PA 15212
**  Meet at the Concierge Desk inside the East Entrance on Arch Street.  **

Who:  This outing is limited to 25 people, first come first served.  You must register by leaving a comment on this blog post by Jan 16 5pm. Include your name + email address and the names of everyone coming with you. (Note: Your information will not appear on the website. The comment will come to me alone.)

Cost: $10.00, cash or check only. (Check made out to the National Aviary.)
* For this special event, admission is free to all who’ve pre-registered.
* Add-ons: Bird shows and feedings will cost the normal rate.

Hope you can make it!  I’m looking forward to seeing you.

For directions and information about the National Aviary, see their website at www.aviary.org

Remember, reservations are required so post a comment to reserve your space today!

UPDATE, JAN 17: The tour is full!

(photo of Hyacinth Macaw at the National Aviary by Christopher Rice at Wikimedia Commons. Click on the image to see the original)



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