All posts by elfruler

DOUBLE CLUTCHES AFTER EAGLET LOSS

UPDATE 12/3/2020:
I have created an entirely new page devoted to Second Clutches, with charts and data and research, and an overview of known Second Broods after the loss of eaglets.  I now know of 3 instances of the latter phenomenon among Bald Eagles, preceding the events at the Southwest Florida nest last year.
The new page is here.

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Here is the original post I published on 4/1/2020.

I’ll admit, I was as surprised as anyone on February 22, 2020 when the eagle pair at the Southwest Florida nest produced a second clutch of eggs after losing their eaglet 27 days after it hatched.  I know of the 8 instances of double clutches seen on streaming cams from 2006-2019, but all of those occurred after the loss of eggs, not eaglets.  Nothing I had read or heard of indicated that Bald Eagles would lay a second clutch of eggs after losing an eaglet.

Until today.

The original first egg at the Southwest Florida nest was laid on 11/12/19 and hatched on 12/19/19. The second egg in that first clutch, laid on 11/16/19, did not hatch.  After the eaglet’s death the parents continued to hang around the nest, bringing in new nesting materials, and they engaged in bonding behaviors and copulation.

On 2/22/20, 38 days after the loss of the first eaglet, the female parent, called Harriet, laid another egg, starting a second clutch, and 3 days later on 2/25/20 she laid a second egg.  The parents then incubated both eggs for the next 37 1/2 days, and on 3/31/20 the first egg of the new clutch hatched.  As of today the second egg has a large hole and the second eaglet seems to be making progress toward hatching.

It turns out that reclutching by Bald Eagles after loss of an eaglet is not unprecedented. I have been doing research on the success and failure of Bald Eagle clutches, and today I came across an article by A.L. Bryan, Jr., L.B. Hopkins, C.S. Eldridge, I.L. Brisbin, Jr., and C.H. Jagoe, published in 2005 in the journal Southeastern Naturalist. The article, titled Behavior and Food Habits at a Bald Eagle Nest in Inland South Carolina, reports observations at a nest in south central South Carolina in 1997, 1998, and 1999.

In the 1997-98 breeding season the nest produced 2 eaglets which fledged in February 1998. The following November the parents began their new breeding season.  I quote from the article:

"In November 1998, the eagle pair initiated another breeding attempt at Pen Branch and at least one nestling was presumed to have hatched (a feeding was observed on 9 December 1998). The pair abandoned this breeding attempt approximately 7 days later for unknown reasons (adult eagles were observed setting on the nest, either incubating eggs or brooding young, on 10 and 14 December). The pair initiated a second breeding attempt at Pen Branch in late February 1999 that produced 2 nestlings. These nestlings were discovered on the ground in dense vegetation by our personnel on 20 May and 7 June 1999, at approximately 55 and 73 days of age. These birds were taken to the South Carolina Center for Birds of Prey where they remained through August 1999, when they were released north of Charleston, SC."

The eaglet from the first clutch was only a few days old when the parents abandoned the nest, whether because the eaglet did not survive, or for some other reason. The authors of the article speculate that the female parent may have been a new mate and was perhaps not experienced in caring for a nestling. But their observations were not close or complete enough to be sure of the reason for the abandonment.

What is interesting from my perspective is that a re-clutch about 2 months after loss of an eaglet successfully produced two new eaglets. The reason why those eaglets did not fledge successfully on their own and ended up on the ground and in need of rescue is unknown.

But now I know that the events at the Southwest Florida nest this breeding season do not represent a first.

WHEN WILL EGGS ARRIVE?

We are only about three weeks away (give or take a few days) from the beginning of the 2019-2020 Bald Eagle breeding season.  As eagleholics already know, Florida eagles, as well as some elsewhere in North America, have been visiting their nests, adding sticks and fluff, courting, delivering and eating prey in the nest, and in a few cases (in Florida) copulating before our very eyes.

To help viewers predict when eggs might be laid at their favorite nests, I have updated my monthly Egg Calendars of eggs laid since 2006 to include last season’s activities.  They are available here.  They can be downloaded and printed out.

The calendars not only give the dates of all the eggs from 2006-2019, but also show whether the eggs hatched and nestlings fledged.  I have included an empty column for 2019-2020, so anyone can add new information to their own copies of these documents as eggs are laid.

The arrival of eggs at a particular nest is remarkably consistent over the years, within a couple of weeks in most cases.  But the timing can change significantly if one or both mates is replaced, the nest is lost or eagles choose to relocate, foul weather interrupts the normal schedule, or intruders challenge for a nest or territory.

I have also updated my list of all the Bald Eagle cams observed online or by reliable ground observers since 2006.  This list includes codes that I use in the Egg Calendars.  The codes are easy to understand: each begins with the abbreviation for the state or province (for example, GA = Georgia, BC = British Columbia), followed by a fairly predictable alphanumeric sequence to indicate the nest (such as shp = Shepherdstown, blf = Bluff City).  In the Egg Calendars, a number follows the nest ID indicating which egg was laid on that date (1, 2, 3, etc.).

Over the next few days I will begin updating Nest Cam Links.  Some of these have changed or will be changed, others are currently offline, others will no longer be broadcast, and some new cams might go online.  I will do my best to keep up with changes as the season progresses, and I welcome help with this.

As always, if anyone notices errors or omissions, including broken links, in these (or any other) pages, please contact me either here or on Facebook.

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.

FEATHERS!

At the Bluff City nest in Tennessee this week (March 17-23, 2019) we are witnessing the three phases of feather development on a growing eaglet. This nest is live-streamed online by East Tennessee State University, and photos are used with permission. Link to the cam.

On Sunday the two eaglets (BC14 and BC15) were covered with their light gray natal down. These fluffy feathers, called “plumulaceous,” grow in tracts, or rows, that are layered more or less evenly across the skin. The feathers are thin and are not good insulators.

On Wednesday for BC14, and then on Thursday for BC15, we began to see the secondary down feathers emerge. This dark gray layer of down can appear as early as Day 6 after hatch. It is thicker and provides better insulation than the natal down, hence is sometimes called thermal down, as it helps the eaglets begin to self-thermoregulate. The secondary down soon will cover the natal down (but does not replace it because it grows from a different set of follicles). In this photo you can see the dark gray feathers appearing between the neat light-colored rows of natal down feathers.

Within a few days, even while the thermal down is still growing, the follicles that produced the natal down will begin to produce “pennaceous” feathers, ones with a central shaft that makes them stiff, and barbs and barbules that lock together. The shaft has blood vessels running through it as it grows, hence the name blood feather, sometimes also called a pen- or pin-feather (adapted from “pennaceous”). These contour feathers, which include the wing and tail flight feathers, will grow over several weeks to create a protective covering of the eagle’s entire body.

Pin-feathers begin to emerge around Day 12 after hatch, and today at Bluff City, right on time, BC14’s and B15’s wings show a thin line of dark brown feathers at the back edge of the wing. The flight feathers on the wings, the remiges, are the first to begin to grow because they are the longest and take the most time to reach their full length.

In this photo you can see the light gray tips of the natal down feathers that are being pushed out by the growing remiges.

So for the next few days we will be able to see all three types of feathers on the Bluff City eaglets: natal down, thermal down, and contour feathers. The contour feathers will eventually replace the natal down completely, leaving only the thermal down underneath. Contour feathers will appear slowly on the back, then the tail, shoulders, neck, head, sides, chest and belly, and finally the legs and feet. The feathers on the backs of the feet will be the last to grow in because the eaglets will only gradually develop the strength and balance to walk on their toes like their parents do, and feathers would not withstand the wear and tear of constant contact with nest materials.

Hatching Eaglet

Here is a rare bird’s-eye (pun intended) view of how an eaglet uncurls itself from inside the egg in the final stage of hatching. This video is of the hatch of BC14 on 3/11/19 at 10:32 at the Tennessee Bluff City cam, operated by East Tennessee State University.  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 new hatchling.  The eaglet has its back to us and its head is down, tail up.

COOPERATIVE BREEDING

Cooperative breeding is a mystery that scientists have spent decades trying to unravel. It occurs among not only birds but also mammals, fish, and even insects. It is not necessarily a mating system per se, but has more to do with how adults care for their young.

Bald Eagle nest video cameras have provided an opportunity for viewers to observe and document 2 instances of cooperative breeding: on Catalina Island from 1992-2007, and near Lock & Dam 13 on the Mississippi River from 2014 through the present (winter 2018). Published literature includes 6 additional reports of cooperative breeding at Bald Eagle nests, in Alaska, Minnesota, Connecticut, New York, Texas, and British Columbia.

Through several pages on this site I attempt to make sense of some of the mysteries of cooperative breeding and explore the behavior among raptors, including descriptions of each of the known cases of cooperative breeding among Bald Eagles.

Click here to get started.

HALIAEETUS LEUCOCEPHALUS

You know what it means.  (DO you know what it means?  The Latinized-Greekish universal scientific name for “Bald Eagle”?  Literally translated “Sea-Eagle White-Head”?  Term established in the 18th century by Swedish naturalist and taxonomist Carl Linnaeus?  Yes, you knew that.)

But can you say it out loud?  Without sneezing or coughing or mumbling?

I couldn’t either until I utilized the ever-handy Google to find someone to say it for me.

I found lots of someones.  Here’s a site that has Americans, Brits, Welsh, Australians, Canadians, Dutch, Chinese, Germans, Italians, Japanese, Poles, Danes, Russians, Spaniards, Turks, and yes, Swedes, and smart people of other nationalities saying it.

Go ahead.  Impress your friends.

HATCHING!

You know about the internal pip, the egg tooth, and the external pip. But do you know about symmetrical hatching, the complexus muscle, gas exchange via the chorioallantoic membrane, nidicolous chicks, and semialtricial species? If you’re interested in a slightly different presentation of hatching, check this out.

UPDATED EGG-LAYING CALENDARS

With the Bald Eagle egg season well underway and heating up, I have updated the monthly calendars of eggs laid at nests on camera to include data from the 2016-2017 season.  These calendars go back to 2007 when the first reliable observations of dates of eggs laid were recorded.  The season begins in Florida in November and stretches through April in British Columbia, Alaska, and the Yukon Territory.

Go here for the January calendar. From there you can navigate to other months.