Monday, February 03, 2014

Do Bald Eagles Mate in Flight?

Do bald eagles mate in mid-air? Do bald eagles mate through their feet? We’ve been asked those questions on facebook, via email, and at Ustream.  The short answer? No. Bald eagles do not mate with their feet or during ‘nuptial flight’. They mate by touching cloacae – the cloacal kiss – while perched securely on a tree limb or in the nest. The male mounts the female’s back, twisting his tail under hers. The two press their cloacae together and sperm passes from his cloaca to hers. As we’ve seen in Decorah and Fort St. Vrain, mating is brief, intense, and takes place fairly frequently while the eagles are in season.



Most readers have probably heard of the bald eagle’s whirling nuptial flight. Mates or courting pairs lock talons and whirl through the air, disengaging before they hit the ground. Writers have suggested that this particular courtship activity might prove flight skill, test pair commitment, and/or arouse the eagles to begin mating. While these are lovely ideas, reality is much more complicated. Courting eagles do lock talons and whirl, but so do immature eagles, adult/immature eagles, and adult eagles who (presumably) aren’t courting.
Brett Mandernack, the biologist at Eagle Valley, suggested that immature eagle talon locking and whirling flight might be a precursor to adult courtship behavior.  While some locking and whirling appears to be antagonistic in nature, like the two adult eagles who crash-landed in Duluth in May of 2013 (http://www.usatoday.com/story/news/nation/2013/05/14/eagles-crash-land-minnesota/2159079/), some is not. Brett has watched territorial adults repeatedly lock talons and whirl, separating before hitting the ground and soaring upward to lock talons and whirl again. “Why,” he asked “would mated adults keep locking and whirling if the behavior was solely antagonistic?” Eagles display remarkable plasticity, varying their behavior in response to environmental changes, including the presence of other eagles. Perhaps talon locking and whirling flight can be made to serve a number of purposes, including courtship. Only the eagles know for sure.



We know that eagles who retain a nesting territory and partner are more productive than those that don’t. But to get to that point, an eagle must first settle in a particular area (probably not too far from its own birthplace), establish a nesting territory, and acquire a mate. Soaring displays and vocalization might help an unpaired eagle attract a mate (look at me!) and demonstrate territorial occupation (this is my place!). Talon-locking followed by whirling flight might provide a non-aggressive response to a potential partner, indicating serious interest. If the eagles pair, food gifts and other courtship activities will quickly follow.

In Decorah, courtship activities begin in late fall. Mom and Dad bring sticks and branches into the nest, eventually adding soft nesting material as courtship deepens. Food is (often) shared. The eagles vocalize together, spend more time in close proximity, and gently peck and foot to indicate their interest in one another. In late January or early February, all of this activity will culminate in copulation, with egg-laying beginning roughly 2 weeks later.

Lake Pepin is a great place to watch eagles soar and talon lock. Go the National Eagle Center’s website for more information about eagle watching on the big lake: http://www.nationaleaglecenter.org/



Sources

Personal Communication, Brett Mandernack

Interactive Behavior among Bald Eagles Wintering in North-Central Missouri
Curtice R. Griffin
The Wilson Bulletin, Vol. 93, No. 2 (Jun., 1981) , pp. 259-264
Published by: Wilson Ornithological Society
Article Stable URL: http://www.jstor.org/stable/4161465

Lifetime Reproductive Success of Bald Eagles in Northern California / Éxito Reproductivo de Haliaeetus leucocephalus en el Norte de California
J. Mark Jenkins and Ronald E. Jackman
The Condor , Vol. 108, No. 3 (Aug., 2006) , pp. 730-735
Published by: University of California Press on behalf of the Cooper Ornithological Society
Article Stable URL: http://www.jstor.org/stable/4151094


Did you know?

Scientists discover the genetic reason why birds don’t have penises
http://www.smithsonianmag.com/science-nature/scientists-discover-the-genetic-reason-why-birds-dont-have-penises-94130874/
Note: This is a pretty frank discussion that includes a video. 

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