What a difference a year makes. All fall, winter and now spring has seen a series of disastrous happenings at the White Rock nest. The big contrast is between the incredible cooperative effort the White Rock pair has exhibited during the past 3 seasons and this year. Each year the pair returned from migration in the same week in early October, then so cooperatively building the nest, even if Dad had to be repeatedly corrected on the way he placed branches and then with Ma laying her first egg on March 13 for the last 2 years we have had the cams running. Their consistency has been so precise -- or coincidental! Then comes 2013!
Not having marked birds makes the rest of the comments largely speculation -- but lets give it a shot!
The 2013 breeding season started last fall with what appeared to be Pa arriving back from migration right on time in early October. But no Ma for several days. The viewers were quick to worry. And then in comes Ma -- but not we believe the right Ma -- and Pa stood back not really accepting her. The lack of greetings between the pair was apparent. Then a few days later in comes a Juvie to replace the first adult female -- the one we thought was Ma. This young lady was so obviously also viewed unfavorably by Pa. Then a few days later we had the "night fight" heard by many. The next morning the lady in charge was a sub-adult wearing a few black feathers in the head and dark band on the tail. Again Pa did not seem impressed with his newest lady.
There was some repair work to the nest but some period of little activity and no eggs. After another exchange everyone thought Ma was back -- but she did not look quite right to many of us. She was too large and bulky. She seemed to intimidate Pa. But to everyone's pleasant surprise the first egg appeared -- but 12 days later than in the previous two years. Then the differences between this new female and the previous years' Ma really began to show themselves. The new lady did not consistently sit the eggs -- she flew off the eggs for the first few nights. And perhaps even more alarmingly, Pa was not sidling up to relieve Ma for incubation duties - something at which he had always excelled. Pa did not seem to want to sit -- except on Ma! This was definitely different. While the female sat incubating, Pa would move in and copulate with the incubating hen -- sometimes repeatedly in a day. But a second egg appeared -- that seemed good.
No behavior of this pair was consistent with the behavior of last year. The female was not sitting consistently and Pa did not seem to be at all interested in that duty. After two or three days of this 'inattentive incubation' behavior I predicted the eggs would not hatch. Eggs need consistent incubation and heating to first raise the egg temperature to initiate embryo development and then the development requires fairly consistent heat to maintain that development. These eggs got neither.
Then came disastrous April 28th -- the 34th day of incubation for the first egg, when the female gets up off the eggs and flies off. Pa does not take over. In comes a sub-adult, probably a female, with much different white in the head and tail patterns than any of the previous ladies of the year. This lady then proceeds to grab at one of the eggs with her bill and then finally picks up the egg with her right foot and moves it out of the nest cup. With the egg in the talon she reaches down, punctures the egg and almost immediately pulls out a partially but poorly developed embryo -- and eats it!
After picking at the embryonic remains a few seconds the invader is bowled over by attacking Ma -- who drives off the invader and stands around in obvious surprise at the changes -- she now has only one egg! After a few moments she too picks at the embryonic materials, eats some parts and then leaves. The "season of the females" was not a good productive year for the White Rock bald eagle territory.
So what happened? Well who really knows? It initially appears that possibly the original Pa did return -- the timing was similar -- but at some point, perhaps after the 3rd female came on the scene, he was replaced. Certainly his behavior with all the hens was considerably different but more different during the latter part of the season than last year. He did not have the bond with any of the females so apparent in the previous years. He showed no signs of being the partner in incubation -- that he so intensely pursued in the previous years. Mounting the incubating hen was certainly different from previous years and something I had never seen or heard of. I believe Pa either did not return to this nest for 2013 or was replaced during the nesting season.
The multiple females were interesting and exciting -- but certainly none were displaying effective motherhood traits. The final big hen did lay a couple of eggs but had very poor incubating habits. Without a cooperative male she could not be expected to effectively incubate eggs, let alone raise young.
I was surprised to see that the "eaten embryo" was about 10 - 12 days incubated. So at least the female mated -- with someone! The mating of the incubating female by the male could not have fertilized the egg as this has to happen before the yolk enters the oviduct. An egg that is laid cannot then be fertilized.
So, have we had the opportunity to witness a new pair taking over a territory from our previous pair? Possibly. Have they learned some lessons to improve their chances of success for next year? Possibly. As most of our viewers know, other cam-viewed nests have suffered similar blows in the past couple of years. Maybe this less efficient behavior is more common than we think. I suspect not. Our White Rock territory just suffered some changes -- perhaps from the presence of so many eagles competing for this prime territory. If you were more suspicious of how the world is turning for the worst, how we humans have over-exploited the resources, how the oil residues, pesticides and heavy metals have entered our one world ocean from the Danube, the Saint Lawrence, the Mississippi, the Ganges or the Yangtze Rivers, then you might think this was more indicative of nature's reaction to that which has already befallen our salmon, our herring, our orcas or.....
More Thoughts on Embryonic Egg Development
Hancock Wildlife Foundation