Category Archives: Tenth Page

The Air Show

Peregrines, Tenth Page

Two juvenile peregrines learn independence in Wilmington, Delaware (photo by Kim Steininger)

June is “air show” month for our local peregrines.  Where the nests have emptied the action is in the air.

After they fledge, young peregrines are dependent on their parents for six to ten weeks while they learn to supply their own food.

Fortunately, as with all predators, they’re born with an instinct to hunt.  Kittens instinctively stalk and pounce.  Peregrines are programmed to chase.  This means they can develop hunting skills without much parental assistance — which is why hacking works.

In their first weeks after fledging, juvenile peregrines chase anything that flies: their parents, their siblings, butterflies, even turkey vultures.

After two to three weeks they begin to focus on prey the right size.  Eventually they capture something, almost by surprise.

In the meantime they play at all the right moves:  chasing, mock dogfights, roll-overs, talon grappling and prey exchanges.

Above a juvenile in Wilmington, Delaware chases his sibling who won the prize.

Keep looking up and you’ll see the air show.

 

(photo by Kim Steininger.  This Tenth Page is inspired by and quoted from page 501 of Ornithology by Frank B. Gill.)

He Stoops To Conquer

Peregrines, Tenth Page

Peregrine falcon, Mo, tucks his wings in a stoop (photo by Chad+Chris Saladin)

Peregrines are famous for speed when diving on their avian prey.  The dive was named a “stoop” because the word means “to bend the head or body downward and forward.”

The stoop is amazing in many ways:

  • Peregrines dive at a 30 to 60 degree angle.
  • They may start the stoop 5,000 feet away from the prey and drop 1,500 to 3,400 feet in altitude.  These distances are exceeded when a falcon sky-dives with a falconer.
  • Land-based speed calculations have clocked them at 100 to 273 miles per hour.  Falconer Ken Franklin sky dives with his falcon at 242 mph.
  • Peregrines can accelerate from 100 to 200 mph in eight seconds according to Ken Franklin.
  • At 150 mph they tuck their wings tight and extend their shoulders, making their bodies into a diamond shape.
  • At 200 mph peregrines pull in their shoulders and extend their heads to become extremely streamlined.
  • Because their acute vision is at a 40 degree angle, they reduce drag and keep an eye on their prey by not diving straight at it.  Instead they spiral downward keeping the prey to the side so they can see it.  Their logarithmic spiral is rarely noticeable from the ground.

Here are three examples of diving peregrines, thanks to Chad+Chris Saladin.

Above, Mo is tucked into an arrow shape in Canton, Ohio.

Below, Rocky at Cuyahoga Valley National Park shows how peregrines hold their wings slightly open at the shoulder.  If he was going faster his shape would be more angular.

Peregrine falcon, Rocky, in wing-tuck stoop (photo by Chad+Chris Saladin)

 

And finally, Dorothy and E2’s son Henry shows off his flying prowess at Tower East in Shaker Heights, Ohio.   His angle of attack is dramatic but he’s not traveling so fast that he has to tuck in his wings.

Peregrine falcon, Henry, stooping in Shaker Hieghts Ohio (photo by Chad+Chris Saladin)

 

He stoops and conquers.

 

(photos by Chad+Chris Saladin. Today’s Tenth Page is inspired by page 122 of Ornithology by Frank B. Gill.)

 

p.s.  She Stoops To Conquer is a play by Oliver Goldsmith first performed in 1773.

Special Gear For Young Fliers

Peregrines, Tenth Page

Juvenile peregrine falcon at University of Pittsburgh (photo by Colette Ross)When young peregrines fly for the first time they’re specially equipped for their big adventure.

Like many raptors, peregrines’ tail feathers are longer in juvenile plumage than in adults.  In peregrines it averages more than a centimeter.  In red-tailed hawks the difference is even greater but the effect is the same.  Longer tails give the birds more lift “by improving airflow over the wings, especially at slow speeds, and by reducing turbulence as air passes over the body.” (1)

The added lift makes the juveniles’ flight more buoyant than their parents’ and is a great help as they learn to fly and hunt.

By the time they molt into adult plumage a year later, young peregrines have mastered the skills they need and are ready for speed.  In the meantime they have special gear to help them fly.

Think of their tails as “training wheels.”

 

(photo by Collette Ross.  Today’s Tenth Page is inspired by and quoted from page 131 of Ornithology by Frank B. Gill. (1))

Feather Atlas

Mothers’ Work

Bird Behavior, Nesting & Courtship, Tenth Page

Mallard with ducklings (photo from Wikimedia Commons)

We tend to think that birds with precocial chicks have an easier time as parents than those whose nestlings are naked and blind at birth, but this isn’t necessarily so.

Ducklings can walk, swim and feed themselves shortly after they hatch but their mobility is problematic.  They have no idea where to find food nor how to stay safe.  All they know is “Stay with Mom!”

Mother leads them to feeding areas and shows them what to taste.  The ducklings peck in the vicinity until they find good food.

Her hardest responsibility is protecting them from danger.  Baby ducklings are tasty morsels for raptors, minks, cats, dogs, large fish and snapping turtles.  If you watch a mallard family day to day you’ll notice the number of ducklings decreases over time.  Mom does her best but danger lurks.

This mother mallard has had pretty good success so far.  Out of 8 to 13 eggs she still has six chicks.

Until they can fly she has mothers’ work to do.

 

(photo from Wikimedia Commons. Click on the image to see the original. Today’s Tenth Page is inspired by page 483 of Ornithology by Frank B. Gill.)

Incubation Chamber

Bird Anatomy, Nesting & Courtship, Tenth Page
Egg illustration by Stuart Lafford from Michael Walters Birds' Eggs, published by Dorling Kindersley
(illustration by Stuart Lafford from Birds’ Eggs by Michael Walters, published by Dorling Kindersley, 1994, used by permission)

Last week we examined a newly laid bird’s egg.  This week things get more complicated.

Eggs are tiny incubation chambers with all the tools needed to transform an embryo into a baby bird.  The right temperature gets the process rolling.

As an egg is incubated the embryo changes and the membranes take on the critical functions of respiration, circulation and excretion. The yolk and albumen shrink as they’re consumed and the shell participates in respiration and bone construction.

This illustration by Stuart Lafford, from Birds’ Eggs by Michael Walters, shows what’s going on inside.

  • The embryo, surrounded by the amnion, floats in a fluid cushion.
  • The yolk is attached to the embryo’s belly and shrinks as its food is consumed.
  • The allantoic sac acts like a sewer collecting excretion from the embryo.  It also functions in respiration because it’s pressed against the chorion for air exchange.
  • The chorion supports all the embryonic structures and acts like a lung, exchanging oxygen and carbon dioxide through the shell’s pores.
  • The shell thins as the baby bird takes up calcium to construct its bones.  The thinning allows for increased air exchange so the growing embryo receives more oxygen.  It’s also easier to break the thinner shell at hatch time.

In a matter of weeks the egg contains a baby bird, and then he breaks the shell.

The egg has fulfilled its role as an incubation chamber.

(illustration by Stuart Lafford from Birds’ Eggs by Michael Walters, published by Dorling Kindersley, 1994, used by permission. Click on the image to visit Stuart Lafford’s website. This “Tenth Page” article is inspired by page 425 of Ornithology by Frank B. Gill.)

Eggs’ Potential

Bird Anatomy, Nesting & Courtship, Tenth Page
Anatomy of an egg (illustration from Wikimedia Commons)
(illustration from Wikimedia Commons)

Eggs are familiar objects that miraculously become baby birds.  The process is so amazing that I’m devoting two Tenth Page articles to it.

Shown above is the un-incubated egg we know so well.  If fertilized before it’s laid, and then incubated, it becomes a bird.  Each component plays a part.

  • Blastodisc or germinal disc:  Potential embryo.  If fertilized and incubated this small circular spot on the yolk becomes a chick.
  • Yolk:  Food for the embryo.  The female’s ovary deposits layers on the yolk to increase its size before ovulation.  Yellow layers are laid on during the day, white ones at night, so the yolk has rings like a tree.  It’s housed in a yolk sac which is why you have to “break” the yolk when cooking.  The yolk is ovulated with the germinal disc attached (cradled by the yolk) so the food is next to the potential embryo even before fertilization.   As the embryo develops, the yolk shrinks.
  • Albumen = Egg White:  Food, water, shock absorber, and insulation from sudden temperature changes.  The albumen makes up 50% to 71% of the egg’s total weight.  It’s laid on after fertilization while the yolk-with-germinal-disc rotates gently in the oviduct.  As the embryo develops the albumen shrinks too.
  • Chalazae:  Because the yolk is rotating during albumen deposition, twists form in the albumen.  Chalazae act like springs and stabilizers to keep the yolk and embryo in place inside the egg.  They’re the white twisted bits in the egg white.  (Totally amazing!  Shock absorbers, insulation, springs and stabilizers!)
  • Inner Shell Membrane:  the first of two membranes that hold the embryo-yolk-albumen together
  • Air Space:  Between the inner and outer shell membranes the air space acts as a condenser for moisture exchange.  This is where the baby bird takes its first breath before hatching.
  • Outer Shell Membrane:  The final packaging before the shell is laid on.  It’s attached to the shell when you crack open an egg.
  • Shell: The female’s uterus deposits calcium on the outer shell membrane to make the hard enclosure for the egg.  The shell has microscopic pores to allow air exchange for the developing embryo.
  • Cuticle:  A thin layer on the shell that adds protection.  The cuticle has caps on top of the pores that close when necessary to protect the embryo.

Eggs have the tools and potential to become baby birds.  Click here to learn how the chick develops.

(illustration from Wikimedia Commons; click on the image to see the original. Today’s Tenth Page is inspired by page 420 of Ornithology by Frank B. Gill.)

How Do They Hatch?

Bird Anatomy, Nesting & Courtship, Peregrines, Tenth Page
Chicken egg hatching (photo from Wikimedia Commons)

Now that the peregrine falcon eggs are ready to hatch: How does the baby bird get out of the egg?   How long does it take from pip to hatch?

Hatching is a strenuous process in very tight quarters. In all bird species it is the chick’s responsibility to get out of his shell, the first big test of his life. His parents do not assist. (Read more here.)

Peregrine falcon chicks take up to 72 hours from pip to hatch with a lot of resting between activities. Here’s what happens:

  1. Absorb the yolk: Just before hatch day the chick fully absorbs the remaining yolk inside the egg. The yolk was its food during incubation.
  2. Get into position: Inside the egg the chick pulls himself into a tuck with his beak sticking out between his body and right wing.  This gives him the leverage he needs to whack at the shell.
  3. Communicate with parents and siblings: The chick peeps inside his shell and his pecking makes noise. His parents know which eggs are alive and his siblings can hear that a chick is ready to emerge. 
    1. From Birds of the World, peregrine falcon account: An observer in a nearby blind, “Nelson could hear chick peeping inside egg before hatching began, becoming louder during hatch; initial pip of shell occurred >72 h before chick broke free completely. In 500 artificially incubated eggs of F. p. anatum, mean time from pip to hatch was 47.8 h. During this period, chick periodically works to break up area around initial pip but rests most of time. Human imitation of parental chip call stimulates chick to vocalize.”
  4. Take the first breath: The large end of the egg has an air sac beyond the inner membrane. The chick breaks the membrane and breathes for the first time.
  5. The pip: The chick bumps the shell with his egg tooth, a curved ridge of his beak that’s sharp enough to crack the shell. He has a hatching muscle on the back of his neck to help him along. In this way he creates a pip hole.
  6. Resting: This is hard work! The chick rests a lot between activities.
  7. Making a seam: After the pip, the chick taps and cracks his shell all the way around. 
  8. Hatchling emerges: When the seam is complete, the chick pushes with his feet to split open the two pieces of the egg. His mother may move the shell away.
  9. He rests and dries off: The chick is tired from this activity so he lies quietly, waiting for his down to dry. Ta dah!

In the photo below, Dorothy examines her fourth chick of 2010. His opened egg shell lies nearby. He is still wet and pink.

Dorothy examines her fourth chick, 22 April 2010 (photo from the national Aviary falconcam at Univ of Pittsburgh)

After hatching the chick’s specialized tools aren’t needed anymore.  The egg tooth falls off (in songbirds it’s absorbed) and the hatching muscle shrinks into just another neck muscle.

(Credits: photo of a chicken emerging from its egg from Wikimedia Commons.  Click on the caption to see the original.  Dorothy examining her 4th chick in April 2010. Today’s Tenth Page is inspired by page 460 of Ornithology by Frank B. Gill.)

p.p.s. In precocial species, such as ducks, the chicks listen to each others’ tapping to coordinate the hatch.  Elder chicks tap slowly, younger ones tap rapidly so that all of them reach the finish line in a 20-30 minute window.

Turning The Eggs

Bird Behavior, Tenth Page

Dorothy turns her eggs (photo from the National Aviary falconcam at the Univesity of Pittsburgh)

During incubation there’s not a whole lot of activity at a bird’s nest except for this:  Mom (or Dad) periodically stands up, stares at the eggs and draws each one toward her with her beak.  She’s not just rearranging the eggs, she’s turning them.

Other than a few notable exceptions, all birds turn their eggs because it’s required for the embryos’ survival.  For instance:

  • The temperature in the middle of a clutch is warmer than the edge.  Birds move the outer eggs to the middle to keep them evenly heated.
  • In the early days of incubation, it’s important that the embryo floats inside the egg while the membranes that support its life are growing and developing.  Turning optimizes membrane growth.
  • Eventually the chorion and allantoic membranes will be pressed to each other and to the shell.  If these membranes adhere too soon the chick will not be able to move into the hatching position later and get out of the egg.  Turning prevents premature adhesion.
  • The albumen (the egg white) is the embryo’s fluid cushion and water supply.  Turning the egg optimizes the fluid dynamics of the albumen so the chick can absorb it properly.

Egg turning is so important that it’s a wonder some species don’t do it.  One notable exception are the megapodes who lay their eggs in compost heaps and let the heat of the decomposing vegetation incubate them.  No turning there!

I’d rather watch a peregrines’ nest where things are happening, if only a bit of egg turning.

 

(photo of Dorothy turning her eggs from the National Aviary falconcam at University of Pittsburgh.  Today’s Tenth Page is inspired by page 460 of Ornithology by Frank B. Gill.)

How Can They Sit For So Long?

Bird Anatomy, Nesting & Courtship, Tenth Page

Dorothy asks E2 to get up so she can resume incubation (photo from the National Aviary falconcam at Univ. or Pittsburgh)

During courtship E2 is very active but now Dorothy has to plead with him to get up off the eggs.  Dorothy herself is able to sit for 12 hours in a snow storm.  How do they do it?

How do birds instantly switch gears from the frantic activity of courtship to sitting on eggs all the time?

They’re cued by hormones.  Here’s how:

  1. As day length increases after the winter solstice, a bird’s hypothalamus releases LHRH (luteinizing hormone releasing hormone).
  2. LHRH triggers the pituitary gland to release LH (luteinizing hormone).
  3. LH increases production of testosterone in males and progesterone in females.
  4. Testosterone triggers aggression, territoriality and sexual behavior.  It’s good at the start of breeding but doesn’t help raise a family.
  5. Progesterone is the “pregnancy hormone” that induces egg production.  It’s only needed for a short time since female birds are only ovulating and pregnant until they lay the eggs.
  6. On the day before incubation begins the hormones switch.  Prolactin, the hormone that promotes incubation behavior, rises sharply while the other hormones suddenly decrease.  In females, LH and progesterone drop off.  In males, testosterone has been dropping since egg laying began.  If the male shares incubation he has a sharp rise in prolactin, too.  On a graph this hormone switch looks like a sine curve.  There’s a moment where all these hormones are low, then prolactin takes off.

In peregrines, both parents have to be ready to incubate at the same time.  Their courtship rituals help get the couples’ hormones in synch.

This whole process may sound as if birds are at the mercy of their hormones but in every species reproduction is chemically tuned for success.  In humans for instance, progesterone and prolactin switch after delivery so that the mother’s body produces milk to feed the baby.  Individual animals whose hormones malfunction do not have live offspring.

So how do birds incubate so nicely?  In a word, prolactin.

 

(photo of Dorothy and E2 from the National Aviary falconcam at the University of Pittsburgh.  Today’s Tenth Page is inspired by page 448 of Ornithology by Frank B. Gill.)

When Will The Robins Nest?

Nesting & Courtship, Songbirds, Tenth Page

American robin on nest (photo by William Majoros on Wikimiedia Commons)

Spring is moving north and so are the robins.  This week a big wave arrived after Monday’s snow.  Now that they’re here, how soon will they nest?

Robins nest later the further north you go.  In 1974 Frances James and Hank Shugart were curious about the conditions that governed their nesting times throughout the U.S.  Using climate data and Cornell nest watch information from 8,544 robins’ nests they developed a model that predicted when robins would nest in a particular region.(*)

The model shows that robins cue on weather.  Hatching is timed to occur when local humidity is 50% and temperatures are between 45 and 65 degrees Fahrenheit.  By April 23, Pittsburgh’s highs and lows are exactly in that range so our birds are getting ready.  Here’s what they’re up to:

  • Robins spend 5-7 days building their first nest of the season. 
  • Egg laying begins 3-4 days after first nest completion.
  • Eggs are laid one per day for a clutch of 3-4 eggs.
  • Incubation lasts 12-14 days.

From nest building to hatching, the first nest takes 26 days. (Subsequent nests take less time.)

Our robins should be nest building right now except for one thing:  Do they have enough mud to begin construction?   Has the mud been frozen?

Watch the robins in your neighborhood to see what stage they’re in.   Join Cornell Lab’s Nest Watch program and your data can become the basis for studies like James’ and Shugart’s that broaden our knowledge of birds.

 

(Credits: photo by William Majoros on Wikimedia Commons.  Click on the image to see the original.
Today’s Tenth Page is inspired by page 260 of Ornithology by Frank B. Gill, portions of which are quoted(*) in this article.)