Wednesday, January 21 2009 @ 04:31 PM EST
Contributed by: davidh
Bald eagles mate from the time of returning to the nest territory in early fall through egg laying, and sometimes a few months after. Like all raptors that I know, the mating takes place when the female is securely standing on a perch, usually a high tree limb, and the males gently lands upon her back, using both his wings to carefully balance, and then curling his tail and cloaca under the female’s tail, which she has simultaneously moved to the side as she turned her cloaca upwards so the two cloaca touch face to face. The sperm passes from his cloaca to hers and then travels up the oviduct to meet the downward flowing ova for the ‘meeting’, the fertilization.
What great moments of trust. These great predators who can instantly kill prey with the sharp and powerful talons are now, so gently and trustfully, coming in direct contact. The trust that allows the female to accept the male's killing talons onto her vulnerable back is quite extraordinary – but it is an essential and ultimate act of the bonding that has been developed between them. No bonding, no trust, no mating, no young, no species!
Lets go back: The Pre-nuptials!!
On October 9, 2002 1030: I was at our Blaine, WA warehouse and heard an adult bald eagle scream – I immediately ran outside as this was the first record of the eagles return since their departure in mid-July when they left the nearby nest with the young. But the intensity and pitch of the call was most unusual. It was the male's higher pitch but the intensity and constancy of the calling was unusual. But I could see no other birds around or direction to his intentions. This was their favorite hunting perch overlooking Semiahmoo Bay so I was used to them being here.
The male continued his calls almost non-stop for over an hour when all of a sudden he changed the pitch and intensity – something was up and I darted outside to see what. He was now standing horizontally on the branch, his head stretched outward to the southern shore of the Bay and his calls were quick and loud. Within a few seconds later and I could focus on the source of his calls – another approaching adult eagle – headed straight at us. The approaching bird stared to scream and it was obviously a female by the deeper call, she circled the calling male and landed on the adjacent tree about 80 feet away. Both birds kept up the calling, and within a few seconds it developed into a “unison” call, with both birds doing the same thing at the same time. Each bird arched its head forward and then upward and backwards over it's shoulders so the head followed about a 180 degree arch – all the time calling in unison. .
I was mesmerized. I had seen this intense behavior before but always later in the year and as a prelude to mating. Within a minute of these unison calls the male took off, flew directly to the female's tree and lighted beside her. Here they continued, even increased the intensity of the calls and head throwing, always in absolute unison. Then it happened. The male jumped up on the female's back and they mated. This was October 9. This was approximately 5 months from her first egg. What was the explanation?
I believe I just witnessed the return of the pair to their nesting territory from the short ten week fall northern migration. But what a reunion, what a reaffirmation with incredible vocal intensity, all taking place on their two favorite hunting perches, and then the ultimate, mating. What a climax to the event.
We know that eagles build and intensify the mutual bond between the pair through aerial displays, and particularly through the described mutual vocalizations and displays. But what I think I witnessed that day was the actual moment of their arrival back at the nesting territory after their separate northern sojourns at the end of the last breeding season, their re-confirmation of the bond, their reconfirmation of each other. In 55 years of eagle watching I have seen a lot of eagle courtship, all the aerial flights, the mutual calling and many matings. But never have I seen it done so intensely, and never so early in the year.
Just 40 miles south of Blaine WA, on the Skagit River, the USF&WS had banded a pair of adult eagles with solar powered satellite tracking devices. Sadly their two young were not tagged. But the story of the adults northern migration was quite astounding. The normal pattern of fledging occurred. The adults quit feeding the eaglets in the nest, after about 3 - 5 days they get hungry and make their first flight with the concerned parents watching. After another week of flying around the nest territory, sometimes picking up food that the adults have been eating nearby, the adults simply fly off and leave the youngsters to their own fate. Harsh but obviously successful.
But this story is about what happened next to the adults. The male, now being tracked by his satellite .....
..... marker headed north up the coast, exactly as we had all predicted that all adults and young do after abandoning the nest. Certainly we know that the thousands of nesting eagles of southern British Columbia were not going south as no big numbers of eagles showed up in Washington, Oregon or California in early fall. So they had to go north. The tagged male finally confirmed our suspicions. About three days after leaving the Skagit area he was tracked fishing for herring in the Prince Rupert harbor, about 600 miles up the British Columbia coast and right at the southern Alaska border. I had banded and radio tagged several eagles during my thesis years in the early 1960's but the technology then only allowed line-of-sight transmission and I never got a reading after the day of release – just too many intervening mountains to give a signal. But now we finally had some direct evidence. Our southern eagles do go north when the nesting season is over.
But that was only half the story. The female when she left the nest literally few the 40 miles north to the British Columbia border, crossed over my house, then turned eastward straight down the US / Canada border, occasionally going back and forth over the border as she worked eastward over the coast range, over the Nelson Range and then the Rockies themselves – only then did she turn north and travel up the east side of the Rockies to Great Slave Lake in northern Alberta. She covered about 1200 miles in 8 days – and spent the fall months probably hunting squaw fish on the lake. Not something we would have predicted.
I tell you the above because the greetings of our two Blaine eagles, their incredible vocalizations and the intensity of the greeting and mating is perhaps not just a casual meeting, but perhaps one that acknowledges that each has undergone some quite long and arduous adventures. And who does not get a fine greeting on such a return!
MATING FOR LIFE
There are a few records of banded eagles or eagles with distinct plumage patterns that have been followed year after year. From these observations it is clear that bald eagles largely return to the same nest year after year and mate with their same partners year after year. This of course does not mean that individual eagles, particularly if they loose a mate during either migration or while on the breeding territory will not take on a replacement partner. The observations overwhelmingly show that a lost partner can sometimes be replaced within days or even hours. Reproducing young is the operative word. It is all good and fine to defend your territory and exclude competition until you need a new partner and then new needs and rules apply. The general rules seems to be that eagles mate for their natural life, reuse the same territory and often the same nest in that territory year after year and generally a pair has a very consistent timing of what they do when. This means that annually you can expect the same pair to migrate, return to their nests during the same week, lay their eggs and hatch their young the same week etc. Iif you observe a significant break in this annual timing of the seasonal activities I believe this is a good clue that one of the partners has been replaced.
NOTE on the accompanying photos: These were taken by Conrad Musekamp, our very keen local photographer, who has spent many seasons watching several pairs of nesting eagles. I have also had the pleasure of using many of his fine shots in my book: The Bald Eagle of Alaska, BC and Washington.