Hanover Bald Eagle Blog # 4 - 2022
Jan. 31, 2022
In partnership with Pennsylvania Game Commission and Comcast Business .
As the Hanover parents have demonstrated year after year, teamwork pays off!
Eagle chicks are large, needy, and have a lot to learn from their parents as they transition from the nest to the outside world. The Hanover male and female share parenting duties for the entirety of the breeding season, with responsibilities spread across both shoulders (or should we say wings).
Raptors use different breeding strategies depending on species-specific factors. These include things like body size, number of eggs laid (called clutch size), and growth rate of nestlings.
American kestrels, which are charismatic and colorful little falcons, lay relatively large clutches of 4-5 eggs, and are what raptor biologist Dr. Bildstein calls 'monogamy light.’ This means that mated pairs stay together for one breeding season but may choose new mates the next year when they return from migration. Bald eagles follow a slightly different breeding strategy: They lay relatively small clutches of 2 eggs, and form monogamous partnerships that can last a lifetime. These are just two examples of different breeding strategies, but they both work — otherwise they wouldn’t have evolved!
American Kestrel. Bill Gracey. CC by 2.0.
Before this year’s eggs arrive, the Hanover eagles will spend time strengthening their bond and checking in with each other. You may see them rubbing beaks, perching side by side, sprucing up the nest, and preening each other (called allopreening), all of which are considered bonding behaviors. At this point in their relationship, the Hanover pair engages in subtle romance. They know each other well, and have little to prove.
When bald eagles are first vying for each other’s attention, however, they go all out.
Cartwheeling is one of several “sky dances” performed by bald eagles during courtship. Biologists theorize that cartwheeling provides a way for eagles to assess the health and stamina of prospective mates, and to assert dominance over a territory. When eagles interlock talons during these displays, they plummet towards the ground at high speeds, vocalize, and then peel off at the last moment just in time to avoid ground collision. Sometimes, it doesn’t end well.
Watch this video of cartwheeling, 35 seconds long.
Juvenile bald eagles practice this behavior before they are ready to breed. As you can see in the video it takes a lot of coordination to cartwheel with such speed and agility. Those of you who have tried ballroom dancing can probably relate — it takes practice to get the moves right. If you ever see two large dark birds locking talons mid-flight and catapulting through the air, you may be watching a juvenile training session. Keep your eyes peeled!
Photos for this blog were generously contributed by Harry Eggens. View more of his beautiful work here, at: www.hewaph.com. We thank him for his stunning photographs and enthusiasm for the avian world!
Sources
Bildstein, Keith. (2017). Raptors: The Curious Nature of Diurnal Birds of Prey. Cornell University.
Buehler, D. A. (2020). Bald Eagle (Haliaeetus leucocephalus), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.baleag.01
Cornell Lab of Ornithology. (2019). American Kestrel Life History. All About Birds.
https://www.allaboutbirds.org/guide/American_Kestrel/id
Gross, Doug (2013, January 1). Breeding Season Begins in Winter. Pennsylvania Ebird.
https://ebird.org/pa/news/breeding-season-begins-in-winter
Written by Zoey Greenberg
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