Tag Archives: clutch

NUMBERS FROM THE NESTS

WILD BALD EAGLES, 2006-2020

© elfruler 2020

The video cameras that have been trained on Bald Eagles’ nests since 2006 have provided a treasure trove of information about the breeding behavior of these apex raptors. In the universe of the more than 100,000 active Bald Eagle nests in North America, the data that these particular nests yield is minuscule. A few published scholarly reports on Bald Eagle nesting success focus mainly on a circumscribed area (e.g. Florida) for 1 or a few breeding seasons. The data here from the nests on cam span 15 years of breeding from 2006-2020 across a wide geographical expanse throughout the continent, and they represent the full range of climates and habits in which Bald Eagles reproduce. (Nests included in the data are listed here.)

Over the period, adult pairs at these nests made 401 breeding efforts at 85 locations, producing 910 eggs, 721 hatchlings, and at least 588 fledglings. These numbers might be considered a fair sampling of breeding data for the species.

The pages and tables that follow break down the data collected via these cameras on multiple levels. The raw numbers of eggs laid, nestlings hatched, and juveniles fledged, from nest to nest and year to year, yield statistics and percentages that give an overall view of breeding success over the 15 years. Burrowing more deeply into these numbers reveals how many clutches are successful over time, and which clutches of a particular size (1 egg, 2 eggs, etc.) are more successful than others. The numbers open a window into losses of eggs and eaglets, and what we can learn about reasons for those losses. And the numbers help flesh out some perceptions of behaviors of nesting Bald Eagles, such as coping with bad weather, predators, and intraspecific intruders (by other Bald Eagles), and replacing a lost clutch.

The data reinforce some facts that are already known:  Bald Eagles typically lay clutches of 2 eggs, with clutches of 3 eggs less common, clutches of 1 egg unusual, and clutches of 4 eggs quite rare. A fair number of eggs do not hatch, but a healthy majority end in successful fledges.

Other details to emerge from these analyses are perhaps more surprising:  While overall averages seem consistent with what is generally believed, there is often a wide range of values across seasons and from nest to nest.  In some years the number of eggs lost far exceeds the average, while in other years few eggs remain unhatched. Similarly, the number of nestlings that die before fledging covers a wide range among the years. Three-egg nests produce a higher percentage of fledges than either 2-egg nests or 1-egg nests; the latter are least successful in producing fledges.

These pages represent a complete revision of data that I published here in 2018, which consisted of a single page and 1 spreadsheet. For this new report I have pared down the nests to include only those with the most reliable observations, mainly the ones with streaming video cams, plus a small number of nests with reliable ground observers. I have also expanded the detail and breadth of information and analysis, resulting in 8 spreadsheets, and I have provided a narrative discussing each one. I have also compiled a lengthy list of References to literature on breeding, eggs, incubation, and survival.

These tables and narratives are presented in sequence in the pages that follow:
Additional new pages also make use of the nest data:
Full references for citations in the following pages are given here:

I began collecting data when I started watching web cams in 2009. Thanks to the Hancock Wildlife Foundation, the Institute for Wildlife Studies, spreadsheets compiled by Judy Barrows, nest cam websites and Facebook pages, and numerous individuals with whom I have communicated, I have been able to stretch the data back to 2006 when streaming cams first began operating. These sources also have been invaluable in filling in gaps in my own observations. I owe all of them a great debt of thanks.

 

EAGLET GROWTH AND DEVELOPMENT

It has long been a dream of mine to collect a daily log of screen caps and videos that illustrate the growth and development of one eaglet from hatch through fledge, and which can serve as a framework for discussion of the many milestones in an eagle’s first 3 months of life.  This year, thanks to the superb camera setup at the Bluff City nest in Tennessee, operated by East Tennessee State University (ETSU), I have been able to realize this dream.

I have created a series of pages that includes a general introduction to eaglet growth and development, daily photos of young BC14 from hatch on 3/11/19 to fledge on 5/31/19, and a list of references.  I will be adding more pages to the series, covering specific eaglet features like feathers, feet, and various behaviors as it grows.

These pages would not have been possible without the assistance and support of Michelle France, camera operator and keen observer at the ETSU nests, who not only expertly zoomed, panned, and tilted the sometimes touchy cam, often catering to my requests, but also created a treasure trove of screen caps and videos every day which has been invaluable in my quest for daily shots.

I also must thank my long-time eagle-watching buddy Donna Young, whose careful observations over a decade have greatly enriched my understanding of eagle behavior.  Our countless conversations have helped shape this project and contributed enormously to the information I have gathered and presented.

The series I am launching today is found under the Menu item “Eaglet Growth” and so far includes:

More pages are in the works.

EAGLET DAILY PHOTOS AND MILESTONES

© elfruler 2019-2020

Click here for an Introduction to this page.

Photos here are from the 2019 breeding season in a Bald Eagle’s nest in Bluff City, TN, broadcast live by East Tennessee State University, and are used by permission.  Click here for link to the live cam.  The focus here is on the elder of two eaglets, BC14.  Many thanks to Michelle France and Donna Young for helping to collect the screen captures and tell the story.

Measurements are derived or calculated mainly from Bortolotti 1984a, 1984c, and 1984d, and Gerrard and Bortolotti 1988 (Click here for References).  Numbers given here are in the ball park but will vary from one eaglet to another.   % indicates the proportion a particular measurement bears to its value at the juvenile’s full size (Click here for information about taking measurements.)

BC14 hatched at 10:32 a.m. on 3/11/19.  The cam provided a rare bird’s-eye (pun intended) view of how an eaglet uncurls itself from inside the egg in the first few seconds of hatching. 

I’ve slowed the stream to 10% of normal speed and added arrows to indicate the back, head, left wing, right wing, beak, tail, legs and feet, egg tooth (yes! the egg tooth!), umbilicus, and receding yolk sac of the hatchling. The eaglet has its back to us and its head is down, tail up.

In the weekly galleries below, click on photos for larger views and to scroll through images.  The numbering of Days refers to the age of BC14; Day 0 is Hatch Day, Day 1 is 24 hours after hatch, etc.  

The eaglet is hatched with pink skin covered by a thin layer of light gray natal down.  The beak and cere are gray, facial skin is dark, legs and feet are pinkish-cream-colored, eye ring is dark and protruding.  The eaglet is weak, with limited mobility, balance, and vision.

HEIGHTWEIGHTBEAK LENGTH
BEAK DEPTH
FOOT PAD
Day 0
7.6cm
91g (2%)
11mm (21%)
9mm (26%)
16mm (11%)

Skin color changes from pink to bluish-gray, feet and legs are cream-colored; cere turns from pale gray to pale yellow.  Steadily gains strength and balance through the week, gaining ability to take food, “swim” on belly with wings and legs, escape from nest cup.  Eyes focusing better, seeking out and imprinting on parents.  Sibling competition begins.  Natal down and egg tooth remain through the week.

HEIGHT
WEIGHT
BEAK LENGTH
Day 6
16cm
300g (6%)
17mm
(F 29%, M 31%)

Skin around eyes becomes lighter gray.  Supraorbital ridge more prominent by mid-week.  Egg tooth disappears.  Cere turns gray, rictus of mouth pale yellow.  Feet are beginning to grow rapidly; talons are beige and growing.  Second down appears as early as Day 6.  Juvenal contour feathers (pin feathers) start to emerge on wings, back, and legs by week’s end; male’s remiges emerge earlier than female’s.  (The contour feathers emerge from the natal down follicles and push the natal down out as they grow.)  Facial bristle feathers emerging around eyes and beak.  Reaching out for food more actively; backing up to nest edge to slice; walking sturdily on hocks; preening, stretching, flapping, and scooting as far out as the nest rails.

WEIGHT
BEAK LENGTH
BEAK DEPTH
FOOT PAD
Day 13
950g (20%)
24mm
(F 45%, M 48%)
19mm
(F 58%, M 63%)
F 88mm (60%)
M 87mm (66%)

Growth spurt begins and size differences between male and female develop, especially in weight, beak length, foot pad, and 8th primary feather.  Females are larger, but males grow earlier and more quickly.  By mid-week, female is gaining 70-180g per day, male 80-150g per day.   Beak and feet growing rapidly.  Talons turn from beige to black.  Second down thickens, approaching ability to thermoregulate.  Some second down is growing on the front of the upper region of the tarsometatarsi.  Wing primary and covert feathers lengthen, pushing out natal down at the tips; primaries grow a little over 7mm per day.  Contour feathers emerge on back, shoulders, legs, and breast.  Rectrices start to emerge by mid-week. Beginning to stand on toes briefly.  Stretching and rousing, pellet casting, resting on the rails.

HEIGHT
WEIGHT
BEAK LENGTH
BEAK DEPTH
FOOT PAD
Day 20
30cm
F 1750g (34%)
M 1500g (37%)
31.6mm
(F 57%, M 61%)
F 24mm (69%)
M 23mm (70%)
F 109mm (74%)
M 108mm (82%)

Growth spurt continues.  Remiges are increasingly measurable. Rictus of mouth is yellow.  Second down covers entire body except on top of head where natal down layer is still prominent (resulting in that famous “mohawk” look).  Head, neck, and side contour feathers coming in.  Pecking at food, grasping and playing with nesting materials, wobbly toe-walking by the end of the week.  Sibling competition transitions into play.

WEIGHT
BEAK LENGTH
BEAK DEPTH
FOOT PAD
8th PRIMARY
Day 27
F 3000g (59%)
M 2400g (60%)
40mm
(F 72%, M 77%)
F 27mm (81%)
M 25mm (83%)
F 125mm (85%)
M 115mm (87%)
Day 27-33
F 64-70mm
M 74-80mm

Energy demands for metabolism and growth peak by Day 30, then weight gain tapers off.  Feet nearly full size by week’s end and are turning yellow.  Stretching, flapping, preening, and more confident toe-standing and -walking. Standing on nest twigs as if on a branch, practicing holding with toes and talons.  Parents hold food further away to encourage reaching; eaglet may lunge for food and attempt to tear off bites with beak; hasn’t yet mastered the skill of holding food down with feet.

WEIGHT
BEAK DEPTH
FOOT PAD
8th PRIMARY
Day 34
F 3500g (69%)
M 3000g (72%)
F 29mm (85%)
M 27mm (87%)
F 142mm (97%)
M 129 (98%)
Day 32-38
F 100-106mm
M 110-116mm

At week’s end the eaglet is about 3/4 of full weight.  Feet are nearly full grown.  Toes and tarsometatarsi fully grown (making banding possible).  Legs, feet, lores, and rictus of mouth are yellow. Stretching and flapping, standing securely, grabbing and mantling food as it is delivered, tearing food more effectively.  Grasping and playing with nest materials with talons and beak.  Vocalizations transitioning from chirps to persistent chittering and loud “squees,” especially at parental visits and food deliveries.

WEIGHT
BEAK DEPTH
FOOT PAD
8th PRIMARY
Day 41
F 3800g (75%)
M 3300g (73%)
F 31mm (88%)
M 29mm (90%)
F 146mm (99%)
M 130 (98%)
Day 37-43
F 136-142mm
M 146-152mm

From Days 40-45 growth of beak and feet slows; feet and legs will be fully grown by Day 50.  Contour feathers on front of the upper region of  the tarsometatarsi emerging.  Wing flapping becoming more vigorous, flap-hopping higher.  Standing on the rails to slice. Long stretches of standing and looking out, or sleeping on the rails.

WEIGHT
BEAK DEPTH
FOOT PAD
8th PRIMARY
Day 48
F 4500g (88%)
M 3500g (88%)
F 32mm (90%)
M 30mm (92%)
F 147mm (100%)
M 132mm (100%)
Day 42-48
F 171-177mm
M 181-187mm

Contour feathers on sides and belly filling in.  Whitish sheaths still visible at bases of remiges and upper- and underwing coverts.  Confident standing.  More effective self-feeding, but still relies on parents for most feedings; grabbing, stealing, and mantling food.  Vigorous flapping, lifting off, enjoying the wind.  May begin branching, perhaps with 1-2 flaps, often by stepping.

WEIGHT
BEAK DEPTH
8th PRIMARY
Day 55
F 4600g (90%)
M 3700g (92%)
F 33mm (93%)
M 30mm (93%)
Day 47-53
F 207-213mm
M 217-233mm

After about Day 60 growth tapers off except beak, hallux claw, and flight feathers.  Some remnants of sheaths at bases of wing coverts.  Juvenal body feathers nearly complete except on wings and tail; contour feathers on flanks still filling in, as well as on the upper region of  the tarsometatarsi.  Axillary feathers (wingpits) mostly white.  Aggressively grabbing and attempting to steal food from parents and siblings.  Flapping results in hovering in mid-air for several seconds.  Siblings watch, mimic, and play with each other.  Branching likely.

WEIGHT
BEAK LENGTH
BEAK DEPTH
8th PRIMARY
Day 62
F 4800g (94%)
M 3850g (96%)
F 54mm (98%)
M 49mm (95%)
F 33mm (94%)
M 30mm (94%)
Day 52-58
F 243-249mm
M 253-259mm
Day 57-63
F 278-284mm
M 288-294mm

Lower leg feathers are thickening.  Aggressive food grabbing, stealing, and mantling.  Confident one-foot perching and preening on branches.  Vigorous flapping and long hovers.  Sometimes stumbles when landing, learning to use wings to regain balance.  Fledging is possible from Weeks 10-13.  Males usually fledge 3-4 days before females.

8th PRIMARY
Day 62-68
F 314-320mm
M 324-330mm

Growth of primaries slows after 72 days.  Branching more confidently, learning to perch, move around, and use wings for balance on branches.  Fledging can occur suddenly and without warning, although eaglet may look intently at nearby branches and appears to evaluate suitable landing spots.  First landing is usually awkward, and eaglet may end up on the ground. 

8th PRIMARY
Day 67-73
F 350-356mm
M 360-366mm

By Day 80 primaries have reached 80% and rectrices 84% of their full length (achieved in the second winter).  Male primaries growth tapers off, but female primaries continue to grow after fledge.  Juvenal feathers will be longer than those of mature adults and will become shorter with each molt until year 5.  Beak and hallux talon not yet fully grown at fledge (they will reach full size by the second or third winter).

WEIGHT
BEAK LENGTH
BEAK DEPTH
8th PRIMARY
Day 80
F 5100g (100%)
M 4000g (100%)
F 54mm
M 50mm
F 35.8mm
M 32.2mm
F 378mm
M 353mm

BC14 fledged unintentionally on Day 81, 5/31/19, but the eaglet was ready.  The branch on which it was perched broke and the eaglet fell but quickly recovered and flew strongly in the direction of trees across the creek.  

The new fledgling juvenile eagle returned to the nest 3 days later and visited several times before dispersing from the area for good.  Its sibling, BC15, fledged 8 days after BC14.

PERSONAL NOTE:  In my opinion the 2 eaglets at this nest in 2019 are of the same gender, either female-female or male-male (it is impossible to know which).  The younger may appear to be slightly smaller, but according to Bortolotti (1986a, 1986b), a younger sibling is almost always slightly smaller than an elder of the same gender.  A male develops earlier and more quickly, but a female eventually is noticeably larger, especially so if she is the elder.  (Male-female broods are quite rare.)  It is quite difficult to ascertain relative size because of the camera angle and lack of perspective, but at fledge I could not see a significant size difference between BC14 and BC15.

 

EAGLET GROWTH AND DEVELOPMENT

© elfruler 2019

The growth and development of a Bald Eaglet from hatch to fledge takes about 10-13 weeks.  Along a spectrum of morphological and behavioral states from least developed (“altricial“) to most developed (“precocial“), raptors fall near the minimally developed end.  Altricial hatchlings have few or no feathers, closed eyes, little to no mobility, no ability to thermoregulate, and need parental care to survive and grow.  Precocial hatchlings have a full layer of down feathers, open eyes, mobility and thermoregulating ability, ability to feed themselves, and are soon able to leave the nest.  Raptors are considered “semi-altricial”:  at hatch they have a thin layer of down but are unable to thermoregulate, their eyes are open or partly open although not yet able to focus or follow movements, they have some mobility, and they are entirely dependent on parents to survive and grow.

Thanks to the work of Gary Bortolotti and Jon M. Gerrard in Saskatchewan in the 1970s and 1980s, we have reliable information on the development of eagle nestlings from hatch to fledge, including weight and growth of the critical beak, feet, and wing feathers.  (Click here for References.)  Beak and feet grow faster than other body parts because they are essential tools for survival and take several weeks to be fully developed.  The “gangly” and “clownish” look of young eaglets is largely due to the disproportionate growth of feet and beaks.

Hatched with thin natal down, eaglets gain a thicker second set of down starting a week or so after hatching, and soon thereafter their body (contour) feathers begin to grow.  These feathers will become the juvenal (first-year) eagle’s smooth covering by the time it fledges.  They take several weeks to reach full length, especially the wing feathers which are not yet fully grown until after fledge.

Steadily emerging behaviors reflect the growth of the eaglet’s skeleton, muscles, feathers, and neurological systems.  As the days go by the eaglet develops the ability to hold up its head, maintain its balance, focus on and follow the parents with its eyes, reach out and eventually lunge for food from the parent’s beak and finally pull bites of food off a fish by itself.  Especially with the emergence of contour feathers, an eaglet engages in near constant preening, using its beak to remove the protective sheaths around the feathers and help the vanes unfurl and its barbs lock together.

It swiftly gains mobility, from pulling itself by its wings and pushing with its legs through the soft nest materials, to standing and walking on its hocks, stepping backwards toward the edge of the nest and tipping up onto its toes to expel wastes over the side, ultimately graduating to standing tall on its toes and walking around like its parents.

As wing feathers begin to grow the eaglet waves its arms and extends them overhead in a full body stretch (which falconers call “warbling”), then builds its breast muscles with vigorous flapping, flap-hopping, and finally catching the air to hover above the nest.  Inbetween all this activity, an eaglet spends many hours sleeping and resting, apparently doing nothing but growing.

The pages here follow the daily growth and development of the two eaglets at the Bluff City nest in Tennessee in 2019, through an online camera operated by East Tennessee State University (ETSU).  BC14 hatched on 11 March at 10:32 a.m., and BC15 hatched a day and a half later, 12 March by about 11:00 p.m.  Photos and videos here are from the Bluff City cam and are used by permission.

Heartfelt thanks to Michelle France, camera operator and keen observer at the ETSU nests, and to my long-time eagle-watching partner Donna Young for her careful observations of Bald Eagle behavior and eaglet development over the years, and her contributions to the descriptions on these pages.

INTRASPECIFIC INTRUSIONS AT BALD EAGLE NESTS

© elfruler 2018

“intraspecific adj. : occurring within a species or involving members of one species.” (www.merriam-webster.com)

Bald Eagles choose their breeding territories and nest sites carefully, driven by factors that will lead to success in raising their young.  These factors include adequate food resources, a sturdy nest platform, available shelter from dangerous weather, ease of defense, and tolerable distance from disturbances.  A good location will be attractive to any Bald Eagles that come along, and it is not surprising that a resident Bald Eagle pair will be challenged by other Bald Eagles for the site, leading to competition between members of the species, or intraspecific conflict.

It is not uncommon for one or both members of a pair to be challenged even before the nesting season begins, resulting in displacement, injury, and even death.  Conflicts that occur once a clutch of eggs has been laid or a brood of chicks has hatched can cause loss of eggs and chicks, despite the fierce defense that the parents inevitably mount against intruders.  Often the parents are successful in repelling a challenge and their chicks fledge.  In rare cases an intruder is accepted by the resident pair as a cooperative breeder (Go here for a series of pages about Cooperative Breeding and its occurrence among Bald Eagles).

The Bald Eagle nests that have been viewed on camera or monitored carefully from the ground since 1992 have provided a glimpse of intraspecific intrusions of many types and with a variety of outcomes:

  • Events before, during, and after the season
  • From one to many intruders
  • Intruding males and females, adults, subadults, and juveniles
  • Replacements, disappearances, injuries, and deaths of parents
  • Unhatched or broken eggs and injured or slain nestlings
  • Double clutches
  • Rescued nestlings and rehabbed fledglings
  • Successful fledges
  • Cooperative breeding

Even careful monitoring of cams and nests don’t provide the full picture of events surrounding intrusions, which often take place out of human view.  Even happenings in full view do not always have clear-cut explanations.

  • How many intruders are in the area?
  • When did they first appear?
  • What encounters occur off-nest between intruders and residents?
  • What is the sex or age of an intruder?
  • Does a resident eagle disappear because it has been injured or killed, or because it has decided that it cannot prevail in a battle?
  • Was an egg broken by an intruder or an agitated parent, or because it was unviable or infertile?
  • Did an egg fail to hatch because intruders interrupted the reproductive cycle and prevented fertilization?
  • Why would one intruder destroy eggs or chicks but another intruder leave eggs or chicks undamaged?
  • Does a resident adult respond primarily defensively to an intruder, or might there be a trigger that precipitates an offensive response?
  • Why would an intruder become a helper and cooperative breeder rather than a threat?

Answers to such questions would provide a much better understanding of events we can see, but too often the answers elude us.

The number of Bald Eagle nests for which reliable daily reports have been made more than doubled from 2008 to 2018 – from 24 to 57.  They range from southern California to New England, from south Florida to Alaska, and many points on the continent inbetween.  The nests are found in a variety of habitats, including rural farmland, along rivers and streams, lakes and bays, in woodlands in parks and wildlife refuges, on coastal islands, college campuses, and in city neighborhoods.  Yet it cannot be claimed that these nests are a representative sampling of all of the thousands of Bald Eagle nests in North America.

Nor can we be sure that we have witnessed every conceivable behavior or outcome associated with intraspecific intrusions.  The information that I present here is illustrative of certain types of Bald Eagle behavior, but should not be taken as a statistical report on intraspecific intrusions.

This first chart (at this link) describes the intraspecific intrusions observed at Bald Eagle nests from 1992 through 2018, the nest locations and habitats, what is known about the intruders, the events, and the outcomes.  (Link opens in a new browser tab.)  Losses (of parents, eggs, or chicks) can result directly or indirectly from intrusions, or they may occur for other reasons not related to intraspecific conflict.  Not every intrusion leads to a loss.

This second chart (follow this link) summarizes the details and gives percentages to enable comparison of intrusions, losses, and fledges from one year to the next.  (Link opens in a new browser tab.)  The percentages are number of intrusion events (nest intrusions, clutch intrusions, eggs lost, etc.) compared to the total number observed (nests, clutches, eggs., etc.) in that season.  (The years 1992-2007 at the California West End nest are not included in this summary because of the outsized effect of DDE contamination on egg production there.)  Notably, for these nests there is no clear trend in the percentages over time.

  • While 2018 clearly was a bad year for nest intrusions (including both before and during a clutch), at 24.6% of observed nests, 2008 was almost as bad, at 20.8% of observed nests.
  • On the other hand, 2008 was a worse year for clutch intrusions (after eggs were laid), at 19.2% compared to 17.9% in 2018.
  • And in 2008, 4.5% of chicks were lost, compared to a much smaller 1.3% in 2018.
  • The number of eggs lost was a staggering 11.3% in 2018, but the 8.6% of eggs lost in 2008 is the second highest percentage.
  • The year 2013 was difficult, with 13.6% of clutch intrusions and 6.7% of egg losses.
  • Some years were relatively benign: 2011 saw only one intrusion and 2012 only two.  A dip in losses occurred in 2015 and in intrusions in 2016.
  • From 2013-2017 most percentages were relatively stable – nest intrusions, clutch intrusions, losses – with an overall dip in 2016. Intrusions and losses in 2018 were severe, and it remains to be seen in coming seasons whether that year was an outlier.
BRIEF UPDATE ON THE 2018-2019 SEASON: I have not yet added new information to the charts, but the number of intraspecific intrusions declined significantly from the year before. Only 6 such intrusions occurred, only 2 of which happened after eggs were laid. 2 nests ended up with no eggs laid, and a total of 4 eggs were lost. No eaglets were lost.

There is no question that suitable habitat for nesting Bald Eagles is on the decline across the continent because of human development and encroachment.  But the numbers we have for these particular nests do not necessarily mean that increasing numbers of nest intrusions point to an approaching saturation of carrying capacity for Bald Eagles across the board.  Each territory has its own conditions that may or may not be either conducive or resistant to nest intrusions.  Increasing population density in a particular area may simply drive some Bald Eagles to adapt by seeking out previously unclaimed territories, by gradually shrinking the size of their territories (over time) to allow for more nests (if the food supply allows for it), or by allowing more instances of cooperative breeding.  It remains to be seen whether intraspecific intrusions will have a negative impact on the Bald Eagle population in the long run.  Some have argued that a rise in population density ultimately could result in a state of population equilibrium by slowing the breeding productivity to offset the long period of increase that followed the banning of DDT in 1972.

While the snapshots that these observed nests provide give us some narratives about intraspecific intrusions at Bald Eagle nests and make comparisons possible, a broader understanding of the causes and effects of such intrusions, as well as a glimpse of what they may entail in the future, must await more detailed and systematic studies (such as Mougeot et al. 2013 in Saskatchewan and Turrin and Watts in the Chesapeake Bay, 2014 and 2015).

For perspective on the Bald Eagle population in North America and trends over time, Partners in Flight (PIF) estimates the number of breeding-aged Bald Eagle individuals in 2017 at around 250,000, based on data from the North America Breeding Bird Survey, an approximate 131% increase since 1970.  The U.S. Fish & Wildlife Service’s oft-cited number of about 10,000 breeding pairs (or 20,000 individuals) in the lower 48 United States in 2007 does not include numbers from Canada or Alaska (both of which exceed the number in the lower 48 states), and it represents only eagles in pairs that are actively breeding.  The PIF estimate encompasses all individual Bald Eagles throughout North America of breeding age whether they have formed breeding pairs or not.  None of these numbers include juvenile or subadult Bald Eagles, which could more than double the totals.

 There is as yet no sign that the Bald Eagle population is declining, whether because of habitat changes that lead to overpopulation and intraspecific conflict in a territory, or other causes such as contaminants, trauma, electrocution, disease, poisoning, and poaching.  In 2010, following the removal of the Bald Eagle from the list of threatened and endangered species, the U.S. Fish & Wildlife Service produced a Post-delisting Monitoring Plan for the Bald Eagle.  The Plan establishes a 20-year monitoring period (roughly four generations of breeding Bald Eagles) in the lower 48 states, with data analyzed and reported to the public every 5 years.  The Plan will yield information on changes in numbers and their causes, and it includes provisions for responding to a 25% or greater decline with corrective action by federal, state, and local agencies, Native American Tribes, and other interested partners.  The Plan specifically references the possibility of re-listing the Bald Eagle as threatened and/or endangered as a remedy to an unacceptable level of decline.

REFERENCES

Dzus, E.H. and J.M. Gerrard 1993.  Factors influencing Bald Eagle densities in northcentral Saskatchewan.  The Journal of Wildlife Management 57: 771-778.

Elliott, K.H, J.E. Elliott, L.K. Wilson, I. Jones, and K. Stenerson 2011.  Density-dependence in the survival and reproduction of Bald Eagles: linkages to chum salmon.  The Journal of Wildlife Management 75: 1688-1699.

Farmer, C.J., L.J. Goodrich, E. Ruelas I., and J.P. Smith  2008.  Conservation Status of North America’s Birds of Prey.  In K.L. Bildstein, J.P. Smith, E. Ruelas I., and R.R. Veit (eds). State of North America’s Birds of Prey.  Nuttall Ornithological Club and American Ornithologists.  Union Series in Ornithology No. 3. Cambridge, Massachusetts, and Washington, D.C., 303-420.

Grubb, T.G., L.A. Forbis, M. McWhorter, and D.R. Sherman 1988.  Adaptive perch selection as a mechanism of adoption by a replacement Bald Eagle.  The Wilson Bulletin 100: 302-305.

Hancock Wildlife Foundation Forum.

Hornby Eagle Group Projects Society.  Our Nature Zone.

Hunt, W.G. 1998.  Raptor floaters at Moffat’s equilibrium.  Oikos 82: 191-197.

Institute for Wildlife Studies.  Channel Islands EagleCAM Forum.

Jenkins, J.M. and R.E. Jackman 1993.  Mate and nest site fidelity in a resident population of Bald Eagles.  The Condor 95: 1053-1056.

JudyB.  Watching Eaglets Grow.

Mahaffy, M.S. and L.D. Frenzel 1987.  Elicited territorial responses of northern Bald Eagles near active nests.  The Journal of Wildlife Management 51:551-554.

Markham, A.C. and B.D. Watts.  Documentation of infanticide and cannibalism in Bald Eagles.  Journal of Raptor Research 41: 41-44.

Mougeot, F. 2004.  Breeding density, cuckoldry risk and copulation behaviour during the fertile period in raptors: a comparative analysis.  Animal Behaviour 76: 1067-1076.

Mougeot, F., J. Gerrard, E. Dzus, B. Arroyo, P.N. Gerrard, C. Dzus, and G. Bortolotti 2013.  Population trends and reproduction of Bald Eagles at Besnard Lake, Saskatchewan, Canada 1968-2012.  Journal of Raptor Research 47: 96-107.

Partners in Flight.

Turrin, C. and B.D. Watts 2014.  Intraspecific intrusion at Bald Eagle nests.  Ardea 102: 71-87.

Turrin, C. and B.D. Watts 2015.  Nest guarding in Chesapeake Bay Bald Eagles.  Journal of Raptor Research 49: 18-28.

U.S. Fish and Wildlife Service.

Watts, B.D., G.D. Therres, and M.A. Byrd 2007.  Status, distribution, and the future of Bald Eagles in the Chesapeake Bay area.  Waterbirds 30: 25-38.

Watts, B.D., G.D. Therres, and M.A. Byrd 2008.  Recovery of the Chesapeake Bay Bald Eagle nesting population.  The Journal of Wildlife Management 72: 152-158.

CLUTCHES, EGGS, and FLEDGES

These numbers come from all Bald Eagle nests for which I have records, including those observed on camera and from the ground.  See here for a list of these nests.  Excluded from these data are nests in aviaries where non-releasable eagles are provided with food, medical, and other care (Carolina Raptor Center in NC and American Eagle Foundation in TN).

Click on the chart to enlarge.

© elfruler 2018

OVIPOSITION (Egg-laying)

By Donna Young and elfruler
Updated 10/27/18

© elfruler 2018

  • Every female Bald Eagle has her own style of laying an egg that is usually consistent from egg to egg and year to year, although some variations in behavior may occur.  Any departure from a previously observed style may indicate a new female.
  • Rough predictions of when a first egg may be laid at a particular nest can be made on the basis of past years, since a pair tends to lay within a one- or two-week timeframe every year.  A significant departure from timing may point to a change of female, male, or both.  Click here for calendars of egg-laying at Bald Eagle nests observed on live cameras since 2006 (arranged by month).
  • Timing of the first egg is the hardest to predict, but second and third (and in the rarest of cases, fourth) eggs will come at 3-day or 4-day intervals (never fewer than about 69 hours, and only rarely after more than 96 hours).  See this page for statistics showing the time intervals at the eagle cams.

We have compiled a list of behaviors associated with egg-laying (oviposition) that we have observed over ten years of watching Bald Eagle cams online.  We divide the signs into three periods: Prelude, The Main Event, and Postlude.  A few signs are seen in all instances of oviposition, but we emphasize that no two events are alike, even with one specific bird.

 

PRELUDE

  • Nest preparation
    • For a few days before oviposition both male and female usually will spend more time in the nest, bringing in and arranging materials, especially the softer grasses, leaves, fronds, etc. that form the small cup where the egg(s) will be laid. They may dig with their beaks in the cup to help define and deepen it.  Exceptions to this do occur – sometimes there is not much soft material to form a clear cup.
    • Also for several days both parents probably will lie for a time in the nest cup, sometimes scraping backwards with their feet and pulling the soft materials in toward the boundary of the cup, all of which helps form it into a clear rounded indention.
  • Behavior
    • The female may begin to exhibit increasing lethargy for a day or few days before oviposition.  She may stand in the nest or lie in the cup almost motionless for minutes or even hours.  This is a great tease, and it may or may not lead immediately to egg-laying.   Observable lethargy does not always occur.
    • In some instances she may be absent from the nest just before oviposition, flying in (probably from a nearby perch) at the last minute.
    • Just before oviposition she may seem restless, lying down and standing up, or circling the nest cup.  She may rearrange the nest materials, dig in them with her beak or scrape with her feet.
    • Her mate may bring her a gift of food in the hours or minutes preceding oviposition, which she will confiscate and usually mantle, and she may whine to communicate that he is to leave it for her.  He will concede.

Female at MN DNR nest, 1/28/17

THE MAIN EVENT

  • Body position
    • The female must be slightly elevated above the nest cup to allow enough room for the egg to come out.  She assumes a squatting or crouching position, either rising from a resting position or moving to the cup from another part of the nest.  This squatting is usually clear, but sometimes, if the cup is very deep or if she is already incubating an egg or two, it is difficult to detect any lifting of her body.
    • The body will be nearly parallel with the nest or at an angle of about 10-15 degrees with the tail low or flat on the nest.  Wings may be pulled in tight or may bulge out slightly.
    • She may look intently down into the nest cup in front of her.
  • Behavior
    • She may unfold and refold one wing and then the other over her back once or several times, and settle her feet into the cup.
    • She may release a small amount of wastes into the nest, clearing her cloaca for the egg.  The tail usually flips up slightly for this.
    • She may remain very still, seemingly unfocused, or she may look around even during contractions.
    • Her body feathers may fluff outward.
  • Contractions may be marked by any of the following:
    • Her upper back and shoulders may constrict clearly with each contraction.
    • Feathers on her nape, back, sides, and wings may shudder, lift, and/or fluff out with contractions.
    • Her wings may flex outward slightly with each contraction.
    • She usually toggles from foot to foot after each contraction.
    • Her tail may rise slightly with each contraction.
    • Her body may tip backward and forward slightly.
    • She may exhale soft whistles and/or chirps with each contraction.
    • She may lower down further into cup, head hunkered into her shoulders.
    • She may spread her wings at the elbow and appear to prop herself on them during contractions.
  • Visible contractions may last as briefly as 1-2 minutes or as long as 7-8 minutes.
  • Final push is always marked by an end of the contractions. It may also be marked by:
    • Shaking and shuddering of the entire body.
    • A final loud chirp or whistle.
    • A quick, sharp flip of the tail.
    • A dramatic jump and spreading up and/or outward or flapping of the wings.
    • Hardly any detectable movement at all, in which case the cessation of contractions is the only clear indication that the egg has emerged.
  • After the final push any of the following may occur:
    • She may become very still for several minutes.
    • She may rise, look around, or shake her head.
    • She may turn her head and quickly wipe her beak on her wing or scapular feathers.
    • She may look directly down into the cup where the egg lies.

POSTLUDE

  • She begins incubating after laying, but this may occur in one of several ways:
    • She may immediately step up and out of the nest cup and examine the new egg, nudge or roll it, lower herself and shimmy her brood patch onto the egg(s), and settle into incubating.
    • She may remain in a squat above the egg(s) for as long as 20-30 minutes, staying still or perhaps looking around before she steps aside to check the new egg.
    • She may stand aside or above the egg leaving it exposed for many minutes before incubating.
    • She may not step aside at all but immediately or after a few minutes simply lower herself over the cup and begin incubating, in which case the egg may not be seen for many minutes or even hours.

elfruler’s YouTube channel has dozens of videos of oviposition at eagle cams from 2011 to the present.

© elfruler and Donna Young 2018

 

 

LINKS TO STREAMING CAMS

The links here point to live streaming cameras of Bald Eagle nests.  All links open in a new browser tab.  Note: YouTube direct links seem to change almost daily, so here I have provided links to a cam operator’s channel, which should list their current Live Cams. Letters in [brackets] are codes I use to refer to the nests. See key and full list of nest codes here.

The list is current as of 9/17/2024, although some cams are offline until the breeding season begins. Please contact me (here) if you discover any broken links, incorrect information, cams coming back online, or new links not included here.

Alaska, Glacier Gardens, Juneau – Glacier Gardens [AK gla]
Glacier Gardens
YouTube channel

Arizona, Pleasant Lake – Arizona Game and Fish Department [AZ gfd]
GFD

British Columbia, Boundary Bay Central – Hancock Wildlife Foundation [BC bbc]
HWF with map
YouTube channel
HWF all nest links

British Columbia, Delta 2, Vancouver – Hancock Wildlife Foundation [BC dl2]
HWF 2 cams with map
YouTube east channel
YouTube west channel
HWF all nest links

British Columbia, Surrey, Surrey Reserve – Hancock Wildlife Foundation and Dawson & Sawyer [BC sur]
HWF 2 cams with map
YouTube north channel
YouTube south channel
HWF all nest links

British Columbia, White Rock, Boundary Bay – Hancock Wildlife Foundation [BC wht]
HWF 3 cams with map
YouTube overhead channel
YouTube north channel
YouTube wide angle channel
White Rock Eagles 3 cams with chat
HWF all nest links

California, Big Bear Lake, San Bernardino National Forest, Fawnskin – Friends of Big Bear Valley [CA bbl]
YouTube channel 2 cams with chat
Friends of Big Bear Valley

California, Folsom, Lake Natoma – Folsom Lake State Recreation Area, Friends of Lakes Folsom and Natoma (FOLFAN), & American Eagle Foundation [CA fol]
YouTube channel
AEF with chat

California, Redding, Turtle Bay – Friends of the Redding Eagles [CA red]
YouTube channel

California, Two Harbors, Catalina Island – Institute for Wildlife Studies [CA cTH]
IWS all nest links with chat
YouTube channel
Explore

California, West End, Catalina Island – Institute for Wildlife Studies [CA cWE]
IWS all nest links with chat
YouTube channel
Explore nest
Explore overlook

California, Bald Canyon, San Clemente Island – Institute for Wildlife Studies [CA mBC]
IWS all nest links with chat
YouTube channel
Explore (cam not yet linked)

California, Fraser Point, Santa Cruz Island – Institute for Wildlife Studies [CA zFP]
IWS all nest links with chat
YouTube channel
Explore

California, Sauces Canyon, Santa Cruz Island – Institute for Wildlife Studies [CA zSC]
IWS all nest links with chat
YouTube channel
Explore

Colorado, Fort St. Vrain – Xcel Energy Fort St. Vrain Station & Raptor Resource Project [CO fsv]
RRP 2 cams (chat on side cam)
Xcel YouTube channel with links to 2 cams

Delaware, Delaware Botanical Gardens, Dagsboro, DE – Delaware Botanical Gardens  [DE bot] NEW CAM FOR 2024-2025
HDOnTap with chat (2 views)
Delaware Botanical Gardens

Florida, Captiva/Sanibel Island – Lori Covert (ground observer), Window to Wildlife, & Clinic for the Rehabilitation of Wildlife (CROW)  [FL cap]
WtW YouTube channel (2 views)
Window to Wildlife with chat

Florida, central – property owner goes by SuperBeaks [FL cen]
YouTube channel with chat

Florida, Miami-Dade County – Zoo Miami, Wildlife Rescue of Dade County, & Ron Magill Conservation Endowment [FL mdc]
YouTube channel with chat

Florida, Northeast coastal – American Eagle Foundation [FL nef]
AEF 3 cams with chat (toggle “Other views” at bottom right)
HDOnTap 3 cams with chat (toggle “Other Views” at bottom right)
AEF YouTube channel with rewind

Florida, North Fort Myers – Dick Pritchett Real Estate, Inc. [FL swf]
Pritchett  with chat
YouTube channel

Florida, Pine Island – Portfolio Medics [FL pin] NEW CAM FOR 2024-2025
YouTube with chat

Florida, Southwest, Eagle Country ranch – EagleCountry.net [FL ece]
Eagle Country multi-view 4 cams (toggle to individual views at top right)
YouTube channel with chat

Florida, Vero Beach –Mullinax Ford [FL ver] NEW CAM FOR 2024-2025
YouTube with chat

Georgia, Berry – Berry College [GA ber]
Berry College 3 cams with chat (toggle button on menu at left)
Livestream cam 1
Livestream cam 2
Livestream approach cam

Indiana, South Bend, St. Patrick’s County Park – University of Notre Dame Linked Experimental Ecosystem Facility [IN ndl]
ND-LEEF
YouTube channel with chat

Iowa, Davenport – Arconic Davenport Works [IA dav]
Arconic
Livestream

Iowa, Decorah Fish Hatchery – Raptor Resource Project [IA dec]
RRP with chat
Explore
YouTube channel
Links to all RRP cams

Iowa, North Decorah – Raptor Resource Project [IA dnn]
RRP with chat
Explore
YouTube channel
Links to all RRP cams

Iowa, Urbandale, west of Des Moines – Denton Homes Iowa [IA urb]
YouTube channel

Kansas, Flint Hills – Farmer Derek Klingenberg’s Farm [KS der]
YouTube Channel with chat

Louisiana, Benton – Metro Aviation [LA ben]
YouTube

Louisiana, Kisatchie National Forest, Kincaid Lake, southwest of Alexandria, Nest E-1 – USDA Forest Service and Kisatchie National Forest [LA kf1]
YouTube channel

Louisiana, Kisatchie National Forest, Kincaid Lake, southwest of Alexandria, Nest E-3 – USDA Forest Service and Kisatchie National Forest [LA kf3]
YouTube channel

Maine, Piscataquis River – Wildlife of Maine Park [ME pis]
YouTube channel with chat

Maryland, Baltimore, Masonville Cove, Helen Delich Bentley Port of Baltimore – Masonville Cove Urban Wildlife Refuge Partnership [MD mas]
YouTube channel with chat

Maryland, Port Tobacco River Park, Charles County – Wild Streaming, Port Tobacco River Park, & Charles County, MD [MD tob]
Wild Streaming with chat
YouTube channel with chat

Michigan, Ann Arbor – Rob Staples’ neighborhood [Mi arb]
YouTube channel 4 cams split view

Michigan, Traverse City, West Bay, Grand Traverse Bay, Lake Michigan –private property owner, goes by Great Lakes Bald Eagle Cam [MI tvc] NEW CAM FOR 2024-2025
YouTube channel with chat

Minnesota, St. Paul – MN Department of Natural Resources [MN dnr] NEW CAM FOR 2024-2025
DNR
YouTube channel

Minnesota, Albert Lea – St. John’s Lutheran Community [MN alb]
YouTube channel

Montana, Miles City – Miles Community College, Yellowstone Valley Audubon, MT Fish, Wildlife, & Parks [MT mil]
AngelCam

New Jersey, Three Bridges, Hunterdon County – Conserve Wildlife Foundation of NJ, Public Service Electric & Gas, NJ Endangered & Nongame Species Program, & USFWS [NJ 3br]
YouTube Channel

New Jersey, Duke Farms, Hillsborough – Duke Farms Foundation [NJ duk]
Duke Farms
YouTube channel

New York, Long Island, Centerport – Bald Eagles of Centerport [NY ctr]
YouTube channel with chat

New York, Iriquois National Wildlife Refuge – Iriquois National Wildlife Refuge & PixCams [NY irq] NEW CAM FOR 2024-2025
YouTube channel with chat
PixCams with chat

Ohio, Avon Lake – Redwood Elementary School [OH avn]
YouTube channel 2 cams

Ohio, Cincinnati, Bortz Family Nature Preserve – Cardinal Land Conservancy, Duke Energy, Laura Carliss Co., LPA, & Louise Taft Semple Foundation [OH cin]
Cardinal Land Conservancy
HDOnTap with chat
YouTube channel with chat

Ohio, Little Miami Conservancy, Little Miami River between Cincinnati & Dayton – Little Miami Conservancy [OH lmc]
Little Miami Conservancy
YouTube channel with chat

Oklahoma, Bartlesville – City of Bartlesville & George Miksch Sutton Avian Research Center [OK brt]
Sutton
EarthCam

Pennsylvania, rural “Farm Country” – PA Game Commission & HDonTap [PA frm]
HDonTap 2 cams with chat (toggle “Other Views” at bottom right)

Pennsylvania, Hanover, Codorus State Park – Friends of Codorus State Park & PA Game Commission [PA han]
HDonTap 3 cams with chat (toggle “Other Views” at bottom right)

Pennsylvania, Pittsburgh, Hays neighborhood, Monongahela River – Audubon Society of Western Pennsylvania, Duquesne Power & Light, US Steel Irvin Plant, & PixCams  [PA pit]
PixCams with chat
YouTube channel

Pennsylvania, West Mifflin, suburb of Pittsburgh, Monongahela River – U.S. Steel Corp. Irvin Plant, Monongahela Valley Works & PixCams [PA wmf]
PixCams 4 cams
YouTube channel with chat

South Carolina, Dataw Island, on Saint Helena Island – Dataw Island Conservancy [SC dat] NEW CAM FOR 2024-2025
HDOnTap with chat

South Carolina, Hilton Head Island – Hilton Head Land Trust, Russell Patterson Law, & Hargray Communications [SC hil] NEW NEST & CAMS FOR 2024-2025
HDonTap with chat
Hilton Head Island

Tennessee, Bluff City, South Holston River – Dept. of Biological Sciences, East Tennessee State University [TN blf]
YouTube channel with chat
ETSU 2 cams

Tennessee, Johnson City, Boone Lake – Dept. of Biological Sciences, East Tennessee State University [TN jns] (nest tree fell in Hurricane Helene, platform & cameras placed in different tree)
YouTube channel with chat
ETSU 2 cams

Texas, Combine, John Bunker Sands Wetlands – John Bunker Sands Wetland Center [TX jbs]
YouTube Channel with chat

Virginia, Dulles Greenway Wetlands, Leesburg – Dulles Greenway Wetlands & Loudoun Wildlife Conservancy [VA dul]
YouTube channel with chat
Dulles Greenway with chat
HDOnTap with chat

West Virginia, Shepherdstown, National Conservation Training Center –Outdoor Channel, U.S. Fish & Wildlife Service National Conservation Training Center, & Friends of the National Conservation Training Center [WV shp]
Outdoor Channel 2 cams with chat
YouTube Channel

Wisconsin, Chippewa Falls – Heyde Center for the Arts [WI chp]
YouTube channel

Wisconsin, Trempealeau – private property owner & Raptor Resource Project [WI trm] NEW CAM FOR 2023-2024
RRP
YouTube channel

Inactive or offline in 2024-2025

British Columbia, French Creek Estuary, Vancouver – Hancock Wildlife Foundation [BC frn]
HWF cam with map

British Columbia, Harrison Mills – Sandpiper Resort & Hancock Wildlife Foundation [BC har]
HWF 2 cams with map
YouTube north channel
HWF all nest links

District of Columbia, Washington, National Arboretum – U.S. National Arboretum (USDA) & American Eagle Foundation [DC arb] (not streaming)
AEF (click on tabs at top for different views)
YouTube Cam A
YouTube Cam B
HDonTAP with chat (toggle “Other Views” at bottom right)

Tennessee, Dale Hollow Lake – Dale Hollow Lake Marina Operator’s Association & Friends of Dale Hollow Lake [TN dal] (not streaming)
YouTube channel

When Will That Egg Hatch?

I’ve compiled and analyzed data from wild Bald Eagle nest cams from 2006-2016 concerning how long it takes for an egg to hatch.

In some ways the numbers support what veteran cam watchers have come to know about parents’ incubation behavior, delayed hatching of the first egg, and how close together hatches can occur in comparison to the minimum 3 days between egg-layings.

For instance, the first egg almost always takes longer to hatch than later eggs. Observations from these nests give us a pretty good idea of how much longer.

And hatches can occur as few as 4 hours apart. But for which eggs in a clutch?  The data tell us.

The data also show some more subtle facts, such as differences in hatch timings between a 2-egg clutch and a 3-egg clutch.

There are some unexpected numbers, such as the average time overall between when an egg is laid and when it hatches.  It’s 36.5 days.  Not 34 or 35.

In fact, the shortest hatch time on record at these wild Bald Eagle nests was 34 days 11 hours 1 minute after the egg was laid.  And that fast time is an outlier in the data.

The longest time on record was 40 days 12 hours 17 minutes.

And whether a nest is in a northern climate or a southern climate seems to make no difference in whether hatching is delayed.

Go here to take a deep dive into the data and my analyses.