Milestones

Birds have developmental ‘milestones’ just like humans. Right now there are so many Bald Eagle nests where eaglets are already two or four weeks old. In others, the parents are incubating eggs. And there are others where the parents are only beginning to start working on the nests. You can see every stage of a Bald Eagles growth from the female laying the egg to their fledging from the nest on the many streaming eagle cameras. Every eaglet is different, just like people and their development will not happen on a single specific date.

Within the overall umbrella of bird development, you might remember Daisy the Duck (see previous blogs for more information on this remarkable little duck). This Black Pacific Duck laid her eggs in the Sea Eagles nest. We knew that the ducklings would jump from the nest 24 hours after hatching if we actually got to hatch – which, sadly, we did not. Those ducklings could see, forage, swim, and take care of themselves without help from the parent. Daisy would, still, gather them up and protect them during the night. Fully independent of their mother, those ducklings would have been ‘precocial’. In contrast, the eaglets are not fully developed, nor are they able to feed themselves, or fly down from their nest. Indeed, they are covered with fluffy down but are unable to regulate their temperature.

It takes from ten to thirteen weeks for eaglets to fledge whereas the ducklings do this at twenty-four hours. Eagles as well as all other hawks or raptors are ‘semi-altricial’. This means that they will be dependent on their parents for everything they need until fledge. Even after fledging, the parents will teach them to hunt and will provide prey supplements for them.

Until the onset of streaming cams, there was very little quantitative information on the development of Bald Eagle Nestlings. Today, there are cameras, often more than one, on nests around the world. You can, at any time of the day, watch Bald Eagles, Peregrine Falcons, Golden Eagles etc. at your leisure. The growing community of citizen birders has impacted the knowledge of avian development and behaviour considerably. We are, indeed, continuing to learn every day. Advances in satellite transmitters means that birds can now be studied after leaving the nest providing much information about foraging, distance from natal nest to establishing their own territory, etc. This blog today is general and non-scientific in its terminology.

Many look at the development of Bald Eagles through three stages: structural growth, feather growth; and behavioural growth. Others attempt to combine feather growth with behaviour and structural development into weekly goals. In fact, I have pondered over this blog and how to approach it for several days because there are different factors that impact development. One of those is gender. There are also studies that have shown that the levels of salt in the diet impact growth while others have examined the amount and quality of prey. We know from studying Red Tail Hawks that if you double the amount of prey and the eyases remain in the nest for several days beyond the average, they are better equipped to fly and hunt. Their overall condition is much stronger. For the purposes of our discussion, I have used evidence from the NEFL Bald Eagle nest in 2021 and the SWFL Bald Eagle nest in 2021 and 2017 (E9). There is one eaglet on the NE nest and two on the SW nest in 2021. The parents on the NE Florida nest are Samson and Gabrielle. Samson was born on this nest on 23 December 2013. He is a little over seven years old. We do not know the age of Gabrielle. At the SW nest, Harriet is in her mid-twenties and M15 is 11 years old. Both nests are located within close proximity to a city – Fort Myers and St Augustine. The Fort Myers nest is unique in that the D Pritchett family has a working farm on the land where the nest is located. They also stock a pond in close proximity to the nest specifically for the eagles. This means that there is always food available. Still, the parents bring in road kill as well as fish from the pond. The NE nest does not have this advantage but nest observations reveal that there is an abundance of food although the variety might not be the same as the SW nest.

Both E17 and E18 were born on 23 January 2021. N24 was born on 8 February.

The first week of their lives, eaglets are covered with fuzzy down. The proper term is natal down. They can sit up but it is difficult to support their heads and focus. You can see the white dot indicating the egg tooth. This will disappear later. They use the egg tooth to break through the thick shell. This is often called the ‘bobble head’ phase. Their heads are big and they do not yet have the neck strength to keep them upright at all times. Their eyes are adjusting to focus. Sibling rivalry might already have started. As the days progress, the eaglets will get the strength to hold up their head and balance it. They will also be able to focus with their eyes so they do not look like they are using their beak like a dart but with a moving target (often their sibling). While the bobble head stage is very cute, it is often a relief when the eaglets are more stable.

SWFL nest 2021. Sibling rivalry began immediately. E17 is on the right and is only two hours older than the twin, E18. This rivalry persists but has dissipated to being only occasional and directly related to feeding.
The egg tooth is clearly present on the eaglet to the left.

By week two, the eaglets will be observed crawling out of the nest bowl. They are not walking. They are crawling. N24 is using its feet and wings to help it get out of the nest cup and up to the pantry. It is five days old! Food is a great motivator! Samson has the little one ‘working’ for its dinner. This helps to strengthen its wings and legs. In the Captiva Florida Eagle nest, Peace climbed out of the nest bowl towards the food on day 2. The inclines of both nests are different. The parents present the eaglets with challenges to help them develop their strength such as stretching their necks, grabbing and holding food, working their legs and wings. It’s like having your own personal trainer!

N24 crawling out of the nest cup on 13 February 2021, 5 days old

The beak will begin to grow and the little ones should begin shooting the ‘ps’ out of the nest bowl by the end of week one or beginning of week two.

N24 doing a great pose to get that PS clear of the nest. Watch out mom!

The eaglets are more observant of their world. They will have doubled in size from the day they hatched and their eyes and beak continue to develop. You will begin to notice that pin feathers are growing in at their wing tips. They will start to stand keeping their balance with these wing tips.

N24 12 days old. Notice the feathers coming in on the wing tip (left side)

More feathers begin to appear on the shoulders and the back and the wing feathers are getting longer as the days progress. They are starting to wing flap and they will try picking up food.

N24 wing flapping, 12 days old

N24 is twelve days old in the picture above and the one below. In the one below, you can also see the pin feathers right at the tip of the wing starting to come in. N24 is also standing for several seconds, getting its balance, and flapping those wings.

N24, 12 days old. Wing flapping.

During the third and fourth week, a pattern of accelerated feedings and growth begins. Head and chest are still showing signs of some fluffy down but more dark feathers are starting to emerge.

E17, SWFL Nest, Age 31 days

The eaglets are actively preening those feathers to help condition them as well as to help stop what some say is an itching as the feathers grow in. There is more wing flapping and the eaglets stand with confidence and stability. During this time you will see attempts at standing and walking. They begin to make some effort at self feeding. They are eating much more at each feeding often lunging at the parent to take the food out of their beak. Many observers say that their crops appear like they could burst! These big feedings often result in the eaglets sleeping immediately after a feeding. This is a ‘food coma’. The enlarged crops are extra storage spaces where food is held before being ‘dropped’ to the stomach. Sometimes people call this accelerated growth period the ‘clown feet’ era because the feet seem to grow way out of proportion to the rest of their body. They will also cast pellets. Pellets are food that is undigested such as fur and bones. Pellets are compressed into a hard shape and regurgitated. This often involves coughing and sometimes the eaglets appear not to want to eat the day the pellet is cast. This level of peak energy demands appears to begin to wane after about five to six weeks.

E18 has its wings dropped while sitting (eaglet on left). Crop is full. 23 February 2021.

Beginning around week five to eight, the eaglets often sit with their wings drooping (getting heavy). Hopping and flapping wings occurs more often. They are very interested in what is happening outside the nest. By the end of this period, they will begin to have more of their juvenile plumage colouration. They will be able to hold food and tear bits. They will begin to mantle food. Mantling is the covering of food with the wings in order to have the prey item to themselves. They will stand for longer periods of time and are able to walk easily by the end of the period.

From week nine to fledging. The feathers will become more defined over their entire body and they will stand for longer periods of time upright. They can stand easily on one leg. The hopping, jumping, and flapping of wings accelerates. They are self-feeding but the parents will also continue to feed them. They will now spend their nights sleeping upright like their parents with their head tucked under their wing. They can easily perch on the edge or rim of the nest and will be branching, hopping up to a branch and back down into the nest. Branching tends to occur from seven to ten days before fledging, generally.

Juvenile feathers are not all in. E9, 2017.
E9 Branching, 2017.
E9 trying out a thinner branch, 2017.

It is always exciting to see the eaglet hatch and sad when they fledge. Unless there is a transmitter or bands, they fledge and there whereabouts often goes unknown. Once they are wholly independent of their parents, the juveniles need to find their own territory and source of prey. Sadly, fifty percent of all first year eaglets perish while ninety percent of all year two eaglets tend to survive. The average age of maturity for Bald Eagles is five to six years although there is a young sub-adult male who is incubating his first eggs with his mate in Minnesota right now.

Thank you so much for joining me today. Stay safe. Be well.

Thank you to the Eagle streaming cams at NEFL and SWFL as well as the D Pritchett family. The scaps came from their streams.

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