Category Archives: Nesting & Courtship

Sinks And Traps

Sink hole in Wales (photo from Wikimedia Commons)
Sink hole in a limestone region of Wales (photo from Wikimedia Commons)

Today’s blog about sinks and traps is not about plumbing …

bathroom sink (photo from Wikimedia Commons)

Last week Michelle Kienholz noticed that the mockingbird family near her office was under predation pressure again. In June half the family was eaten by a red-tailed hawk. On Friday two flightless young were frightened to the ground.  Michelle put them in a thick bush and hoped for the best.  I thought to myself, “That place is a biological sink for mockingbirds.”

Like a sink hole, shown at top, a biological sink is where a species breeds but the habitat works against them so they always fail to produce enough young to replace themselves. The population sinks at that site.

A sink can be offset by a high quality habitat called a biological source where the population more than replaces itself.  If the sources equal the sinks the population remains stable.  If the sources outweigh the sinks the population grows.  This balancing act is called source-sink dynamics.

Sometimes a sink is so attractive to breeders that they’re drawn to it in large numbers even though they always fail.  These ecological traps cause localized population crashes.

A good example of an ecological trap is the effect that outdoor lights have on mayflies.

Mayflies lay their eggs on water, often at night.  To find water in the dark they look for the polarized light reflection of the moon on water. Unfortunately, our outdoor electric lights are like thousands of moons that reflect off artificial polarizing surfaces — asphalt, cars, windows, etc.  The mayflies mistake these false surfaces for huge bodies of water and land there to lay eggs.  The locations are both sinks and traps.  All the mayfly eggs are wasted.

Mayflies on a car at Catawba Island, Ohio (photo by Rona Proudfoot on Flickr, Creative Commons license)
Mayflies on a car at Catawba Island, Ohio (photo by Rona Proudfoot on Flickr, Creative Commons license)

The number of mayflies that fall for these traps can be astonishing.  In June 2015 in Wrightsville, PA on the Susquehanna River, there were so many mayflies on the Route 462 bridge that the surface became slippery with dead mayfly bodies.  They had to close the bridge.

I suspect that if they’d turned off the streetlights while the bridge was closed, the trap would have disappeared, the mayflies would have gone elsewhere, and there would have been less to clean up.

(credits: video from WGAL-TV via YouTube.  photo of car with mayflies by Rona Proudfoot on Flickr Creative Commons license. All other photos from Wikimedia Commons. Click on the images to see the originals)

Eagle Productivity Drops For a Good Reason

Juvenile bald eagle at Hays, H8, 23 June 2018 (photo by Dana Nesiti)
Juvenile bald eagle at Hays, H8, 23 June 2018 (photo by Dana Nesiti)

Bald eagles have made an amazing comeback since the days of DDT.  From less than 900 birds nationwide in the early 1960s to more than 20,000 in the U.S. in 2007, their population more than doubled in Pennsylvania in the last 10 years.

At some point the number of nesting bald eagles will reach Pennsylvania’s carrying capacity.  What happens then?  How do bald eagles respond to match available food and nest sites?   We can look to Virginia for the answer.

Since 1964 the Center for Conservation Biology in Williamsburg has monitored and mapped bald eagle nests in the James River watershed.  Every year they do a flyover of the entire area to count both nests and chicks. Their eagle population grew from none in 1976 to a record 289 nests in 2018.  Meanwhile the number of chicks per nest — called “productivity” — rose sharply in the early years of recovery and now is dropping.  CCB announced this trend in two articles:

To see how this works, I have made a slideshow of two graphs from the Center for Conservation Biology’s article.  The bar chart is the count of nesting pairs, 0 to 289.  The line chart, the arc, is the average number of chicks per nest, 0 to 1.6.

As you can see, the number of nesting pairs continues to increase while the number of chicks per nest moves down.

CCB reports that in 2018 the number of chicks reached 1.09 and adds, “The two opposing trends appear to continue the population’s path to stability.”

“Productivity decline” sounds bad but it’s actually good news.  Breeding eagles respond naturally to accommodate lots of adults in the habitat.

So what does this mean for Pennsylvania’s bald eagles?

If the James River experience applies here, we’ll still see an increasing number of bald eagle nests that will eventually average one eaglet per nest.  We know bald eagles can produce more if they need to.  The good news is, they don’t need to.


p.s. See how rapidly the James River nest count grew!   Click here for CCB’s maps of the James River bald eagle population, 1990-2017.

(photo of juvenile bald eagle H8 at the Hays nest site by Dana Nesiti. Slideshow of two graphs from the Center for Conservation Biology article Eagle Productivity Continues to Slide.)

Gannets Galore!

Northern gannet in flight, Cape St. Mary's, NL (photo from Wikimedia Commons)
Northern gannet in flight, Cape St. Mary’s, NL (photo from Wikimedia Commons)

A week ago, on a Partnership for International Birding trip to Newfoundland, we visited Cape St. Mary’s Ecological Reserve during a rare fog-free moment.  Our goal was to see nesting seabirds up close at Bird Rock, one of the most accessible sites in the world.

Bird Rock is one of many cliffs at Cape St. Mary’s but it’s unique because it’s separated from the mainland by a deep chasm only a few feet from the trail’s end.  The birds are safe from land-based predators yet we could see them easily.

The main attractions are 24,000 northern gannets (Morus bassanus) who spend their lives on the ocean but return to Cape St. Mary’s every spring to breed with the same mate at the same nest.  Almost as large as bald eagles, their wingspan is 5.75 feet but they don’t weigh as much.  I love them for their size, sleek beauty, and their ability to plunge-dive at 50 mph to catch fish in the sea.

From the Visitors Centre we walked the trail across the barrens to get to the viewing area.

The landscape on the trail out to Bird Rock, 11 July 2018 (photo by Kate St. John)
The landscape on the trail out to Bird Rock, 11 July 2018 (photo by Kate St. John)

Pretty soon we could see the nesting cliffs. The white areas are all gannets.

Seabird nesting cliffs as seen on our walk out to Bird Rock at Cape St. Mary's, Newfoundland, 11 July 2018 (photo by Kate St. John)
Seabird nesting cliffs as seen on our walk out to Bird Rock at Cape St. Mary’s, Newfoundland, 11 July 2018 (photo by Kate St. John)

Near the trail’s end, Bird Rock is in the foreground.

Bird Rock and the cliff behind it are coated with birds, Cape St. Mary's, NL, 11 July 2018 (photo by Kate St. John)
Bird Rock and the cliff behind it are coated with birds, Cape St. Mary’s, NL, 11 July 2018 (photo by Kate St. John)

Here’s what we saw when we got there.  This 2011 video below (not my own) captures the sights and sounds of the colony.  The only thing you’re missing is the fishy smell of guano. It was filmed when most of the birds were still courting, wagging their heads and touching bills.  When we visited last week they were further along. Some chicks had already hatched.


The gannets hunt far and wide for fish to feed their chicks.  Just around the corner from Cape St. Mary’s in Placentia Bay there are loads of fish near Saint Bride’s. This YouTube video from 2017 (not my own) shows what I love most about gannets. They dive straight down to the sea!

Gannets galore!



p.s. The white spouts aren’t whales. They’re the splash-back from the gannets’ precision dives.

(first photo from Wikimedia Commons; click on the image to see the original. videos from YouTube. All other photos by Kate St. John.)

Growing Greener

Hope perches near a plant growing in the nestbox at the Cathedral of Learning, 24 June 2018 (photo from the National Aviary snapshot camera at Univ of Pittsburgh)
Hope perches near a plant growing in the nestbox at the Cathedral of Learning, 24 June 2018 (photo from the National Aviary snapshot camera at Univ of Pittsburgh)

The peregrine falcon nestbox at the Cathedral of Learning is growing greener.

A plant sprouted near the front perch and grows a little every day.  The seed probably came from the crop of a bird the peregrine family ate for dinner.  We’ll have to do some weeding when the nestbox is cleaned next fall.

Click here for a current view of the plant.

A NOTE REGARDING THE STREAMING VIDEO CAMERA:  The National Aviary’s streaming video contract lasts six months and will expire some time this summer, perhaps soon.  The stream will resume in February 2019 when the nesting season gets underway again.  In the meantime, see snapshots of the nestbox at this link.

(photo from the National Aviary snapshot cam at Univ of Pittsburgh)

Scenes Of Cardinal Family Life

Northern cardinals (Cardinalis cardinalis) are common backyard birds that we often take for granted though their family life is interesting.

Bob Kroeger photographed cardinals nesting in his Cape Cod backyard in May and June.  The slideshow lets us pause and see what they’re doing.

The male is very bright red:  This is good news for the family. Studies have shown that males with bright red breasts and females with bright underwings show more parental care to their young.

He feeds his mate at the birdbath:  The male’s job is to feed his mate from nest building through brooding (and perhaps beyond).  This makes sense because male cardinals don’t have brood patches.  The females build the nest, incubate the eggs and brood the young.

She’s eating away from the nest:   It’s perfectly normal for the female to spend time away from the nest, even if there are eggs in it.  During incubation, which lasts 11-13 days, the female spends 30% of daylight hours away from the nest.

Two juveniles on a branch with their father:  This cardinal couple beat the odds. The majority of nests fail due to predation.

How to recognize juvenile cardinals:  The juveniles resemble their mother but their beaks are dark.  (Adults have orange-red beaks.)  The juveniles’ beaks will turn orange-red when they are 65-80 days old.

You can’t see the food in the father’s beak:  The parents feed insects to their young but they  carry the food far back in their large beaks.  Researchers probably find this frustrating when they have to identify what the young are eating.

How long will the young depend on their parents?  Juvenile cardinals are completely dependent on their parents for about 19 days.  Around that time, their mother starts to build her next nest. Dad may feed the youngsters occasionally until they are 25-56 days old.


(photos by Bob Kroeger of South Dennis, MA: photos on Facebook; his business website.)

Nests Over Water

Green heron, Florida, March 2018 (photo by Bob Kroeger)
Green heron, Florida, March 2018 (photo by Bob Kroeger)

Why does this bird have his crest raised?

Perhaps someone came too close to his nest.

Green herons (Butorides virescens) are shy waders in swampy thickets, preferring to fish in the shadows and nest alone.  Because of their secretive nature it’s always surprising to find a nest.

When green herons return to Pennsylvania in the spring they’re already paired up for nesting.  The male chooses the location, usually in a small tree over water, giving preference to last year’s site if it was successful.  He starts to build the nest but as soon as his lady gets the hint his job is to bring the sticks as she places them.  Then she lays 4-5 eggs.

Green heron nesting in Florida, March 2018 (photo by Bob Kroeger)
Green heron nesting in Florida, March 2018 (photo by Bob Kroeger)

With this dual building effort it’s amazing that the structure is sometimes so thin that you can see the eggs through it from below.

That is, if you can find the nest.  Green herons don’t want you to.  They fly away loudly if you come too close.  Typically they sound like this (Xeno Canto 147343 by Paul Marvin at Viera Wetlands, FL)

… but if they’re really annoyed they are much louder (Xeno Canto 145806 by Paul Marvin at Viera Wetlands, FL)

Right now most of Pennsylvania’s green herons have young in the nest and the parents are busy bringing food.  At 16-17 days old the chicks will climb out of the nest — or swim if they have to.  They’ll fly at 21-22 days old.

Stay alert for the sight and sound green herons.  You might find a nest over water.

Bob Kroeger found these herons in Florida.


(photos by Bob Kroeger of South Dennis, MA. Bob photographs birds for fun and shares them on Facebook. Here’s his business website.)

Tarentum Peregrines: The Week To Watch

June 15, 2018:

The Tarentum peregrine family is already fun to watch. Now the excitement is ramping up.

Back on June 5, Gerry Devinney captured this video of the adult peregrines escorting an osprey away from their nest.  On June 8 Mary Ann Thomas wrote about them here: Tarentum Peregrines Defend Their Nesting Success.

Last Tuesday evening, June 12, the first nestling ventured out of the nestbox to ledge walk and exercise his wings.

We don’t know the chicks’ exact ages but they’re somewhere between 32-36 days old today. Young peregrines fledge at 38-45 days old.  These birds will fly soon, maybe within a week!

Visit the Tarentum boat launch to watch the youngsters get ready to fly.  Click here for a map.

UPDATE, June 15, 6:10pm:  Rob Protz reports that there are three (3!) young peregrines out of the nestbox this evening.


(video by Gerry Devinney)

Tiny Rails

  • A Virginia Rail out in the open. Why is it visible? (Mittry Lake, AZ, 23 April 2018. photo by Steve Valasek,

The further south you go, the earlier the birds nest.  In late April we’re excited that Virginia rails (Rallus limicola) have just returned to Pennsylvania.  In southern Arizona they already have families.

Steve Valasek found this out when he went looking for black rails (a very rare bird!) at Mittry Lake in Yuma County, Arizona on 23 April.  He didn’t find a black rail but he did find tiny rails that were black.

When he spotted a Virginia rail out in the open he wondered, ” Why isn’t it hiding like they normally do?”  In this slideshow of his photos you’ll find out why.

Read about Steve’s adventure on his blog: Virginia Rails.  See full size photos here.


p.s. The Second Breeding Bird Atlas of Pennsylvania says the median egg date for Virginia rails in our state is 6 June. Since the eggs are incubated for 19 days and the chicks are precocial (they walk from the nest), the right time to see a Virginia Rail family in Pennsylvania would be early July. Good luck! They’re usually impossible to find.

(photos by Steve Valasek)

Peregrines at the Graff Bridge

Adult peregrine at Graff Bridge, Manorville, 7 June 2018 (photo by Kate St. John)
Adult peregrine at Graff Bridge, Manorville, PA, 7 June 2018 (photo by Kate St. John)

Yesterday Patience Fisher and I went birding in Clarion County. On the way back I said, “Let’s go look at peregrines.”

Promising a view of peregrine falcons can ruin one’s credibility but I was hoping to see them at the Rt 422 Graff Bridge near Kittanning.  I thought they’d be there but their nesting status hadn’t been confirmed yet.  So why not try?

As soon as we got out of our cars in Manorville I heard and saw a begging juvenile calling from the power tower.  Before I could get him in the scope he left the tower, pursuing another peregrine.

We walked the Armstrong Trail in the direction the two birds flew.  Finding the adult pictured above was easy.  She was perched on the bridge catwalk, looking down into the trees below, and kakking.  Elsewhere under the bridge — not nearby — we heard another begging juvenile.

Success!  I borrowed Patience’s cellphone to digiscope the adult.

We certainly saw one adult and one juvenile. I think the distant begging sound was a second juvenile.  Here’s how I reached that conclusion:

Guess #1:  The first juvenile pursued the adult to that area of the bridge but he landed below in a place she considered unsafe, so she was kakking to tell him to move.  I’ve seen this kind of interaction at Pitt.  Kakking means “I see danger.”  Kakking without dive-bombing means the danger is not a predator to be driven away — so the danger is something else.

Guess #2: I think there are two juveniles.  The other begging call was far away from the original action and its tone sounded like a juvenile who thought it couldn’t/wouldn’t fly to pursue the adult.

Guess #3:  The adult was female.  This is the shakiest guess of all.  Could have been the male.

If you’d like to see these birds for yourself, visit the viewing area soon.  Click here for directions.


(photo by Kate St. John; thanks to Patience Fisher for loaning her cellphone)

Watch Nesting Ospreys

Feeding the chicks at the Hellgate osprey nest, 5 June 2018 (photo from Cornell Lab Hellgate Osprey cam)
Feeding the chicks at the Hellgate osprey nest, 5 June 2018 (photo from Cornell Lab Hellgate Osprey cam)

If you miss seeing nesting peregrines on camera here’s a raptor family to watch online.  As of last night (June 5), there were two chicks and one egg still to go at an osprey nest in Montana.

The nest is in Hellgate Canyon next to the Clark Fork River in Missoula, Montana.  It looks like a very public place but the birds are right next to the river.  The Hellgate valley is so narrow here that the river, the railroad, some businesses, and Interstate 90 are all close by.  We see and hear I-90 traffic in the background. (Click here for a map of the site.)

Louis and Iris are devoted parents whose lives are sometimes complicated by terrible weather and threats from challengers.  And yet they persist.  In this video clip Louis brings Iris a fish to eat while she was incubating last week.  Click here for a 36 minute video of the first chick’s first feeding.

The chicks are tiny.  There’s plenty to see.  Tune in here to watch their progress at the Hellgate Osprey nest.


p.s. If you watch before 7:15a Pittsburgh time, you’ll see that the sun hasn’t risen yet in Montana!

(photo from tweet of Cornell Lab’s Hellgate Osprey nestcam)