Lawrence Peregrines: incubation process

April 4, 2020 in In the Nest Box

Let’s take a look at the overall incubation process and what happens in the early stages! 2020.0402.LPBoth sexes have paired lateral brood patches. Less well developed in male. Belly area may function as patch also but less edematous and vascular than breast (TJC).  In this photo, the male is taking a break on outside edge of the nest box.  He waited a while until the female showed up and set down on the perch pole outside the nest box.

Incubation Period

The peregrines at this location have usually incubated their eggs for 29 to 33 days. In the early days of brooding it’s important to keep the eggs as close to their ideal incubating temperature as possible. If it is too hot or too cool and the eggs won’t develop properly. Later in the incubation process, proper temperature isn’t quite as important.  After a couple of weeks the falcons will be able to leave the eggs uncovered for longer periods of time.  Sometimes leaving the eggs uncovered frequently, or for long periods can mean that the eggs hatch a few days later than normal. This is a very well protected nest box in a location where the resident peregrines will not be disturbed, so they will tend to incubate steadily until the eggs hatch.

According to Derek Ratcliffe, the eggs of the peregrine falcon are among the most handsome laid by any species of bird!  He notes that the prevailing color is reddish-brown with a wide variation.  The surface of the fresh egg has variable amounts of bright red-brown markings appearing as a freckled, mottled, or blotched layer which can easily be rubbed off when the shell is wet. This non-fast layer of pigment gives a peregrine egg much of its beauty and richness, and in fresh specimens is often accompanies by a kind of bloom!

During the normal course of incubation, one of the adults is nearly always on the nest. Exceptions are during disturbance, for short periods on particularly warm days, or for a few minutes during food exchanges. The female does the majority of incubation. The male brings food to her several times daily, or sometimes simply relieves her and takes a turn on the eggs while the female eats, preens, and relaxes. When she returns to the nest box to relieve the male, he usually is waiting on the outer edge of the nest box. It is often a a challenge to identify the male from he female, as the male’s leg band is not always easy to see.  It will be helpful to identify field marks to distinguish the sexes.

Embryonic Development

Many questions have come in about exactly what happens during incubation, in terms of embryonic development.  It is a fascinating question and related to the very mystery of life, and how young peregrines develop inside the egg. So, what happens when?

Over the next number of days, we’ll look a bit closer at how the embryo develops.  Resources will include two book on avian embryonic development and an old blog, specifically about peregrine falcons, that includes a number of entries on this topic.

The age of the embryo when the egg is laid varies. Peregrines tend to lay eggs during the night or early morning or in the evening.; if the egg is not complete until later in the day, it will probably not be laid until the next day. The rate of development of the embryo once the egg is laid also varies. If the eggs are cooled after laying, development of the embryo ceases until the temperature rises again. Development can resume even after the eggs have been cooled for several days. The temperature of eggs incubated by their mother is 106 degrees Fahrenheit The temperature of course will vary when the peregrine leaves the eggs to eat, etc. All of this affects the rate at which the embryo develops and, therefore, how long it takes for the chick to hatch.

The first 4 days are essential. A lot is going on in those 4 days. Let’s have a closer look inside the eggshell. It is a magic journey through the universe of the dawning of life itself.

First Day: The Journey Begins

Before the Egg is Laid:

* The egg is fertilized.

* The zygote divides and begins to grow.

* The cells segregate into groups of specialized function.

* The embryo nearly stops growing between laying and incubation.

During Incubation:

* The area pellucida and area opaca of the blastoderm develop.


Second day:

*27 hours: The alimentary tract appears.

*28 hours: The brain crease begins to form.

*29 hours: Somites appear.

*31 hours: The brain and nervous system begin to form.

*32 hours: The head fold begins to form.

*34 hours: Blood islands appear.

*35 hours: The eyes begin to form.

*37 hours: The heart begins to form.

Third day

*52 hours: The ears begin to form.

*58 hours: The heart starts to beat

Fourth Day

*76 hours: head turns to the left

*78 hours: Amnion has enclosed the embryo

*80 hours: Allantois begins to form

*88 hours: The beak begins to form.

*92 hours: The leg begins to form.

*94 hours: The wings begin to form

Literature cited:

White, C. M., N. J. Clum, T. J. Cade and W. G. Hunt. 2002. Peregrine Falcon (Falco peregrinus), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.

Ratcliffe, D. 1993. The Peregrine Falcon. 2nd ed. Carlton, England: T. and A. D. Poyser.

Cade, T. J., J. H. Enderson and J. Linthicum. 1996a. Guide to Management of Peregrine Falcons at the eyrie. Boise, ID: The Peregrine Fund, Inc. (Excerpt: Linthicum, Janet. Observing Breeding Behavior)

Veldhuis, Froona, Embryo: the first four days, Sept. 6, 2008,

Lawrence Peregrines: 2020 Egg #2!

March 26, 2020 in In the Nest Box

Conditions: overcast skies, wind NW at 7MPH, temp at 35F; forecast for today – partly sunny, with a high near 51. Northwest wind around 8 mph and tonight -mostly cloudy, with a low around 33. Northeast wind 3 to 5 mph.


Great news this morning about 10 minutes before sunrise time, checked the nest box web cam and egg #2 has been laid overnight! This first image was captured through the webcam about 6:40AM. At first look, the female was out of the nest box, and then returned minutes later. Normally, the eggs are laid 48 hours apart, but there may be variations. We’ll expect the third egg on Thursday morning. Until the next to last egg is laid, the female may only incubate form time to time unless the temp is a bit cooler.



Later in the afternoon as the sun came out and the temperature warmed up, the female was seen incubating both eggs!

Lawrence Peregrines: 2020 Egg #1!

March 22, 2020 in In the Nest Box

It was a cold start to this Sunday, with temperatures in the upper teens to 20s, under a clear sky and subtle breeze.  This afternoon, under sun-filled skies, temperatures only rebounded back into the upper 30s. The wind chills were in the upper 20s through most of the day. Tonight, the Peregrines will have increasing clouds, with a low around 24. Southeast wind around 6 mph.

2020.0322.LPMade a visit to the extended Clock Tower area late Friday afternoon, and checked on the activity around the nest box and the extended Clock Tower. It was fairly quiet and the female was seen from the street and through the webcam. She was mulling around inside the nest box. Checked again this morning and wonderful surprise in seeing the first egg for 2020!

Later in the afternoon, she spent a more time incubating the egg, and basking in the later afternoon sunshine! Recently, her behavior was very consistent with the general lethargy that a female falcon typically experiences in the few days prior to laying the first egg. In many cases this lethargy may last a week or longer. She lazes around and spends lots of time in the nest box, nest scraping, and other courtship related activities.

2020.0322.1-001Incubation usually will not begin until the second to last egg has been laid. In this cool spring weather, with night time temps in the low 30’s, the female will spend some time incubating the egg, but it may not be a non-stop effort! The female has a silver federal leg band on her right leg; and a black over green 38/BV band on her left leg.  The male has only a silver right leg band and no band on his left leg.

Lawrence Peregrines: almost a week!

April 11, 2019 in In the Nest Box, lawrence peregrines

Had a nice opportunity to watch the female in the nest box this morning.  Just before 7AM, she raised herself up a bit and changed positions but remained over the 4 eggs.  Then at 7:07AM, she departed for a few minutes and returned to the box, and then back to incubating the eggs. During incubation, an observer may spend lots of time watching very little activity.  The peregrines take turns brooding the eggs. Typically, the female incubates about 2/3 of the time, often for four or more hours before the male relieves her. Males brood for shorter periods– typically 2 to 3 hours, and they brood less frequently. While one adult is brooding, the other may be out hunting. Brooding falcons still need to eat, after all. If they’re not hunting, the other falcon usually stays close to the nest.  The photo on the left shows the female sitting on eggs quietly and with great comfort.  She will adjust as she needs to but is not fidgety as the male tends to be!


Sometimes while the female is brooding the eggs, the male will bring her food that he has hunted. She’ll eat the food, sometimes inside, and other times, outside the nest box while he takes a turn incubating, but then she’ll come back and take over– provided she can get him to move off the eggs. If he doesn’t move right away, she may stand in the nest box and wail at him. Wailing has different meanings for falcons, but in general it indicates dissatisfaction with the current situation.  Here they are together, inside the nest box at around 10:35 AM today, and she is wailing on him big time.

IMG_9571So if this female wails at her guy while he’s incubating, or in the nest box it’s her way of telling him she’s not happy that he’s still standing around, or sitting on the eggs. As with most other interactions between male and female peregrines, the female usually gets her way, though sometimes it takes a while for him to get the message!  Guess who’s usually walking away, with his head bowed low, after getting wailed at….the male!

Lawrence Peregrines: Egg #4!

April 5, 2019 in In the Nest Box, lawrence peregrines

2019.0405-001Checked on the nest box just after 6AM this morning under fair skies, wind from west at 9MPH, and temp at 31F. The forecast for today calls for mostly cloudy skies, with a high near 47. Light and variable winds becoming south 5 to 9 mph in the afternoon. For tonight, rain and snow likely before 1am, then rain. Low around 36. South wind 6 to 8 mph. Little or no snow accumulation expected.

After waiting almost an hour for a look this morning, the adults had a shift change at 6:53AM and this provided a quick peek at the 4th egg!  This egg was likely laid at some point overnight.  Had kept a close eye early evening last night and had a clear sighting of just 3 eggs just before sunset, with little egg laying movement seen up until dark settled in.

So now, the Peregrines shift into full and shared incubation duties that will last the next 30 days or so!  We are about a week ahead of last year’s egg laying time frame. With God’s grace the circle of life continues!

Lawrence Peregrines: addled egg, not hatching

May 18, 2018 in In the Nest Box, lawrence peregrines

Just after sunrise at 5:17 AM it was mostly cloudy, wind from NE at 13 MPH and temp at 58F.  The forecast calls for mostly sunny skies, with a high near 60. East wind forecast at 11 to 13 mph.

IMG_6837The female was observed around 6:20 AM this morning feeding those always hungry and growing chicks!  The fourth egg has not hatched, and at this point, it is unlikely to hatch.  In prior years, the falcons have had unhatched eggs.  An unhatched egg, may also be referred at as an addled egg.  This is an egg in which the developing embryo has died. Not to be confused with a clear or infertile egg, though in common usage the term is often applied to any egg gone bad.

IMG_6852Around 6:20 PM, after a lot of vocalizing, the female was provided with another meal, by the male for the chicks.  The photo shows the female returning to the nest box, with prey in her bill.  The bird in her bill has been stripped of feathers and is ready for her to rip apart for feeding purposes.  Also visible is the remaining unhatched egg.  This type of egg becomes known as as addled egg. Addled eggs are usually left, and may survive after the young have gone as dried and bleached relics, kicked to the side of the nest box, but they are often broken and trampled to pieces!

Literature cited:

Ratcliffe, D. 1993. The Peregrine Falcon. 2nd ed. Carlton, England: T. and A. D. Poyser.

Lawrence Peregrines: feeding time!

May 16, 2018 in In the Nest Box, lawrence peregrines, Peregrine Falcons Eastern Massachusetts, Peregrine Falcons Massachusetts

The three chicks started off the morning under fair skies, calm winds, and temp at 56F.  The forecast for the day ahead calls for partly sunny, with a high near 61. East wind 3 to 8 mph.  Had nice looks at morning feeding session just after 5:30 AM, and the three chicks were very hungry and eager to gobble up the offered prey from the female.  The fourth and final egg remains unhatched.  Hopefully it will hatch some later today!

2018.0516-001Most brooding of the small young is performed by the female, though the male occasionally takes short turns.  No attempt is made to share brooding simultaneously.  Apart from weaker motivation for brooding, a male still has greater difficulty in covering a full brood of chicks than a clutch of eggs. Although the actions of the brooding falcon are essentially similar to those of an incubating bird, there are slight and gradual adjustments appropriate to the change of covering delicate but growing nestlings.  Leaning forward and stepping around gradually cease, but shuffling movements become important, evidently to place the feet below the chicks.  Rocking stops on hatching, and other settling motions are replaced by gentle lowering of the body onto the nestlings.

Literature cited:

Ratcliffe, D. 1993. The Peregrine Falcon. 2nd ed. Carlton, England: T. and A. D. Poyser.

Lawrence Peregrines: #3 Hatch!!

May 15, 2018 in In the Nest Box, lawrence peregrines

2018.0515.2-001Had a nice chance to watch the peregrine chicks at noon today.  Hoping to get a glimpse under the incubating female for an update on number of hatchlings.  At this point almost 48 hours has passed since the second egg hatched, and the clock is ticking!  Finally, at 12:05 PM, the male entered the nest box bearing lunch and the two engaged in a classic food exchange.  In the process the female rose up and off the eggs, providing a clear view of the two hatchlings and the two remaining eggs.  It also meant we might be closer to the third egg hatching later in the day.  If we look back, the third egg was laid almost 72 hours after egg number two, so we are right in the zone for the next hatch to take place.


2018.0515.3-001Was only able to get a brief look a few times during the afternoon, and each time, no movement off the eggs.  Checked at 5:22 PM while driving home, and to my great delight, the female had departed and the nest was wide open.  A quick survey showed a clump of white in the middle, two broken shell halves nearby, and what looked to be a final intact shell in the foreground…the third chick had hatched and joined the brood.



2018.0515.4-001A few moments later, the female arrived into the nest box bearing prey and she started to feed the three chicks!  What a beautiful sight!  The tenderness and care that the female shows while feeding these little ones is so very special.  She is turning her head and craning her neck so that the little chicks will receive the food that they need and that will help them grow!



2018.0515.5-001The last image, and perhaps, favorite of the day, shows the three little newly hatched chicks eagerly stretching their necks forward and gaping tier mouths to receive the fresh pray from mother bear.  Given the amazing process of carefully incubating these eggs over the last month, we now have front row seats to watch this year’s family start their lives with love, care, and tenderness from very attentive parents!  This truly is the circle of life in the animal kingdom and it is always a precious sight to behold!



Literature cited:

Ratcliffe, D. 1993. The Peregrine Falcon. 2nd ed. Carlton, England: T. and A. D. Poyser.

Lawrence Peregrines: third hatch?

May 15, 2018 in In the Nest Box, lawrence peregrines, Peregrine Falcons Eastern Massachusetts, Peregrine Falcons Massachusetts

Just before 6 AM, the peregrines started the day with fair skies, wind from the south at 3MPH, and temp at 61F.  The forecast for the day ahead calls for a chance of showers and thunderstorms, then showers and possibly a thunderstorm after 5pm. Some storms could be severe, with large hail, damaging winds, and heavy rain. High near 83. Light southwest wind increasing to 6 to 11 mph in the morning. Winds could gust as high as 26 mph. Chance of precipitation is 80%. New rainfall amounts between a quarter and half of an inch possible.

A line of storms will move through between 3pm-9pm, and will likely affect the evening commute. Some of these storms could be strong/severe.  This is the forecast from the Storm Prediction Center in Oklahoma, indicating the most likely areas to see severe weather tomorrow.  With any strong/severe storm cells, the greatest threats will be strong/damaging wind gusts as well as heavy rain.  As with any thunderstorm, severe or not, lightning is a danger.

2018.0515.1-001The female was seen incubating and brooding first thing this morning.  She didn’t move for the longest time during my morning watch….no way of knowing if third egg hatched?  All eyes are upon the likely remaining two eggs, waiting for them to hatch.  In most years, the eggs tend to hatch close to one another in a fairly well synchronized way, and within 24 – 48 hours of each other.  We have seen the remaining egg shells around the hatchlings.  The adults may move these around a bit with their bills.  They may seem to nibble a bit on the broken pieces, but they don’t have a well developed habit for disposal of the egg shells.  For the most part, the remaining pieces of egg shell will become trampled.  The hatchlings have a delicate white down at birth, with none of the coloration that will come later with true feathers.  They form a feathery white cluster in the first few days and remain in very close contact with one another as though in a rugby scrum!

Lawrence Peregrines: 2 hatchlings!!!!!

May 14, 2018 in In the Nest Box, lawrence peregrines, Peregrine Falcons Eastern Massachusetts, Peregrine Falcons Massachusetts

This morning started off with overcast skies, wind from the south at 5MPH, and temp at 53F.  The forecast for the day ahead calls for mostly sunny skies, with a high near 75. Southwest wind 3 to 7 mph.

2018.0514.1-001Looks like the second egg hatched last evening!  At 5:45 AM this morning, the female was observed nestled over the hatchlings and two remaining eggs.  One of the little fluff balls was seen peeking out from underneath the mother’s protective cover.  At 6:07 AM, the female rose up, walked to edge of nest box and departed, showing the two hatchlings and two remaining eggs.  She returned within a minute with fresh prey in her talons.  It was a small dark bird, but unable to make a positive identification.



2018.0514.2-002She spent a few minute tearing off the feathers, and then at 6:15 AM, she started to feed the little ones.  She rips up very small pieces and carefully feed the chicks.  She took her time and the chicks gobbled up all that was offered.  Just before 6:30 AM, the female grabbed the remains in her bill, and departed the nest to dispose of the carcass.



Now let’s take a look at an overview of growth and development over the next 40 days.  Here’s a bit of what to expect:

At 5 days after hatch, their mass has doubled. The eyas can sit with relative ease, and the open eyes are more round.

At 6–8 days of age the second down (mesoptile or preplumulae) starts to emerge, first on humeral and alar tracts but no down visible on belly at 6 day, although on the legs and belly at 8 days. Also second down is well out on the wings and looks a bit blueish and sheaths of primaries breaking skin on wings.

By 10 days of age the second down is complete and uniform and outer rectrices are breaking skin. At 10 days, primaries growing at 2–3 mm/d, rectrix sheath not yet split.

At 14 days the second down is dense and long, rectrix sheath about 2 mm and typically ninth primary emerges from sheath.

By day 17 the contour feathers start to push out prepennae and only pale (buffy) tips of rectrices have emerged but growing at about 2 mm/d (since day 13).

By 10 days of age the second down is complete and uniform and outer rectrices are breaking skin. At 10 days, primaries growing at 2–3 mm/d, rectrix sheath not yet split.

At 14 days the second down is dense and long, rectrix sheath about 2 mm and typically ninth primary emerges from sheath.

By day 17 the contour feathers start to push out prepennae and only pale (buffy) tips of rectrices have emerged but growing at about 2 mm/d (since day 13).

At 20 days while still with heavy coat of second down, brown contour feathers are visible on margins of wings, tail, and faintly around the eyes.

By 30 days young appears about half down-covered and half feathered; while side of face well feathered, crown still covered with down.

At 35 days while mostly feathered, large conspicuous patches of down around legs, under wings, and on crown.

At 40 days almost fully feathered with traces of down on crown and under wings and outer several remiges; rectrices not fully grown but bird capable of weak flight.

Literature cited:

Veldhuis, Froona, Eyases growth and development