Re Delta 2, Lafarge, White Rock and Mission, BC Nests

Bald Eagle Biology

Hi All:  The season at times progresses slowly but the season is indeed advancing.

The Delta 2 pair, like so many pairs each year, give us predictability and change at the same time.  The eagle is largely driven by the light cycle -- each bird may respond differently but each bird is relatively constant in its migration dates, egg laying dates etc. from year to year.  The next pair may be a week or two or even three different but each pair will remain fairly consistent year to year. A prime example is the Lafarge pair that has laid its first and subsequent eggs on exactly the same day for each of the last 3 years.  This tells me that at least the female is the same bird in each year.  The White Rock pair in 2011 and 2012 laid its first egg on March 13 but this year changed by 12 days.  I suspect those 2 consistent years were due to the same female occupying the nest but this year I believe at least the female, with a new light periodicity, has taken over the territory.  From some of the recent observations on the male's behaviour, or appropriate lack thereof, the male may have also changed. if only we had banded birds to tell!

At Delta 2 we have fairly consistent egg laying dates - up to 4 days variation from last year to this year, but the same dates in 2011 and 2012.  Ok, possibly the same female bird this year.  I would like to have seen even greater consistency to state more emphatically that we have the same female but 4 days in a year is not much difference.  But I suspect this is near the limits of the individual variation for this area.

What is even more consistent for the species is the hatching of the eggs in 35 days.  Sure, some do differ but largely this difference I suspect is due to whether the pair fully starts the incubation immediately upon laying the first egg. Or do they not sit adequately to bring up the egg temperature to the right 99.6F degrees, the temperature that starts to develop the embryo.  Some birds seem to only sit part time and it is suspected that this does not raise the temperature adequately to initiate the embryonic development.  Under these conditions, where the temperature has not started the development of the first egg, a high enough temperature may not be achieved until the second egg is laid and consistently incubated. This can result in the first egg not hatching for 35 to 37 days after laying.  Sometimes an egg is buried in the nest cup and does not get heated by the eagle's body effectively, thereby delaying the incubation period.  Of course the real incubation period, the time from the beginning of embryonic development until hatching, may still be 35 days.

My point is that for the Delta 2 pair, where I believe we have seen 'solid' incubation from the laying of the second egg laid on March 10, that we should expect the first hatch to be about 35 days later on April 10- 12 and the second egg 3 days later.  If I was a betting man I would wager on it hatching late in the day on the 14th  -- lets say 7:35 pm to make the odds greater!

Update on the Mission Pair:

Mission Pair:  I believe this new pair, "Jack & Jill", is going to be successful in terms of eagles, but not in terms of rewarding our viewers and particularly Percy and Debbie, who so magnanimously gave of their time and facilities to get our cams installed. However, the pair has built another nest a few hundred yards south of the nest we have the cams in, in a tree next to where their original nest tree, which fell down in 2010, was located.  Good for the eagles but not good for us.  

While we have seen the pair on occasion use the cam nest as a resting platform, they are now clearly nesting across the road and have been seen incubating.  So disappointing.  If you are in the area you will see them hunting the Hatzic Lake as before.

We hope that one or more of the local ground observers will still keep us posted on the pair's progress.

Thanks, Debbie and Percy -- we appreciate your good spirit.  Thanks, Pam, for moderating the thread and zooming the cam, along with the other zoomers.

We also thank SHAW Cable who supported the site with their cable connections.

Lets give these birds our best wishes as the world is a tough place for living creatures.


David Hancock

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