Owls and Eagles Hanover Eagles Blog #2 - 2022
January 17, 2022
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Owls and eagles: Nest Competition
Written by Zoey Greenberg • In Partnership with Comcast Business and Pennsylvania Game Commission • Powered by HDOnTap
The Hanover eagles are sprucing up the nest with straw and cushy materials in preparation for eggs, as can be seen from this recent snapshot:
However, a challenge has been developing slowly this season — a great-horned owl is clearly interested in the nest. On December 31st, an owl sat down in the Hanover eagles’ nest bole (an intentionally-created depression to hold the future eggs) for half an hour! We've seen the owls enter the nest with prey and calling out near the nest. Watch latest owl highlight here.
Great horned owls begin courtship even earlier than bald eagles, accompanied by territorial vocalizations and duetting, during which the male and female trade off hooting. In Pennsylvania, great horned owls begin advertising their territory as early as September. Duetting typically begins one-to-two months before the first egg is laid. Eggs are laid in January or February. This owl schedule could bode well for the Hanover eagles; if the great horned owls who have been scoping out the nest were serious about taking over, they likely would have made a stronger move by now. That being said, the Decorah eagle nest in Iowa faced a similar threat in 2015, and the owls remained interested in the nest well into January.
If the Hanover eagles are unable to defend their nest from the owls, they will probably try to build elsewhere. Depending on how early they make this decision, they could have time to construct a suitable nest in time to breed. Bald eagles have built nests in as little as four days, but typically it takes several months. There are likely different factors that influence the time it takes to reconstruct, such as how experienced the pair is, how well they work together, how long it takes them to find another site, and whether the area is saturated with other breeding eagle pairs.
Great horned owl pairs remain in the same territory over a long period of time, yet they do not build their own nests, and they rarely use the same nest two years in a row. They nest on ledges, cliffs, on the ground, or, more often, they use the already-constructed nests of other birds. Red-tailed hawk nests are their favorite. Bald eagle nests are approached less frequently, which is understandable — eagles are fierce, and more than double the size of great horned owls! Although great horned owls pack a punch, they will opt for an easier takeover than an eagle nest, if possible.
Great horned owls lead particularly crafty lifestyles and are known among raptor enthusiasts as a species that doesn’t mess around. Most of us would agree, though, that the Hanover eagles are up to the task of staking their claim and fighting off competition that comes their way. Hopefully the great horned owls will give up on the Hanover nest. And yet, the owls need a place to raise their family too. Perhaps we can offer them kind wishes in finding somewhere else to settle down.
Above from Left to Right are screenshots from two live cams on our network, Great Horned Owls that have nested in a barn in Arizona and an abandoned Eagle nest in Blackwater Wildlife Refuge.
It’s worth remembering that humans often have a direct influence on the availability of nesting sites for a wide range of birds. Strong old trees and dead snags offer nesting platforms for species like bald eagles, great horned owls, red-tailed hawks, and other magnificent raptors. When possible, we should do our part to leave such trees standing. By leaving nesting structures standing, we help reduce the likelihood of territorial aggression over nesting sites. The more the merrier!
Fun Fact: Female great horned owls are larger than males, but they have a smaller syrinx, and therefore a higher pitched hoot than the males. Next time you hear a duet, see if you can tell who’s whoooo.
Artuso, C., C. S. Houston, D. G. Smith, and C. Rohner (2020). Great Horned Owl (Bubo virginianus), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.grhowl.01
Raptor Resource Project Blog. (2015, January 22). Owls in N2. https://raptorresource.blogspot.com/2015/01/owls-in-n2.html
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Raptor Ecology Specialist - Zoey Greenberg
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