First Egg at Sidney Bald Eagle Nest - On CAM
Friday, March 05 2010 @ 09:39 PM EST
Contributed by: davidh
What a week in the life of HWF:
A "First Egg at Sidney" and a "New Executive Director"
A big week for the Hancock Wildlife Foundation!
I must speak to Sidney Ma & Pa -- we always count on them being precise. Delaying laying this year by 3 days from last year is just not the preciseness we count on! ((Officially the first egg will be recorded at 6:38PM March 4, 2010))
But let's rejoice in "An egg at last". Let's hope two more follow. There is data that many species can adjust the quantity, and certainly the schedule, of eggs laid. Will this mean that since the Sidney pair have done so well the past few years that they will rest this year? I doubt. Two or three young seems to be the Sidney production. And more importantly, the Sidney environment is very productive. The shoreline, the fields and the road kills keep generating volumes of food.
What sets the egg laying date?
The timing is of course quite variable ....
The timing is of course quite variable ....in some species, generally locally determined by weather or particularly weather that migrant birds are subject to just before arriving at the nest territory. Do they get delayed by cold fronts, frozen lakes, no insects? Of course our eagles have been on the breeding territory for some months and are perhaps more keyed into the preciseness of the light cycle than to weather. The length of daylight drives their biological clock. Hence, our eagles generally lay their eggs in the same week every year. If not so, this is a very good clue to the possibility of one of the pair being new.
Each individual can have a different but consistent biological clock. The pair bonding, with a lot of mutual behaviors, is designed to bring the pair into a common cycle. But as we have seen, neighboring pairs can be a month apart in their laying the first egg.
The bonding process is directed to bringing both members of the pair in synchronization. The building of the nest, the territory calls and defense and ultimately the matings need to drive that egg from the oviduct at the right time for fertilization, for laying and incubating during reasonable weather, for hatching when food is available to feed the voracious appetites of young, and to fledge the young when they can reach the easy-to-catch dying salmon.
I have not seen any evidence that our Sidney pair has changed one of the partners this season but many of you will have had more intense viewing than I. And of course, this season being almost, within 3 days of last year, the same timing really confirms this. I joke about their imprecision. But 3 days out of 365, without a calendar to check off, does imply some biological clock is working very precisely.
Historically of course our eagles were pushing their nesting season to coincide with the short season associated with the melting of the ice as the glacier retreated and salmon began to populate newly available stream beds. The glaciers are now many miles north. The season of course is still tied to how the main food supply is seasonally available to feed their newly fledged young. For our coastal bald eagles the availability of easy food is absolutely tied to the dead spawned out salmon carcasses. These carcasses are available in the more northern rivers first. Then as the northern rivers freeze up the carcasses are only available farther south. Hence the natural movement of juvenile and adult eagles coincides with these basic salmon spawning runs.
Then at the other end of the season, our locally breeding pairs end up coming back to their nesting territories very early in the year to both defend their territory and start the cycle over again.
This seasonal movement pattern, at least in broad sweeps, means that our south coastal bald eagles arrive back on the nesting territory as early as October, stay in residence all fall and winter and then of course through the spring nesting and summer rearing season. In fact our resident eagles are often only away from the nesting territory about one to two months.
The more northern nesting birds, even those of central BC or SE Alaska, are not all on their territories until as late as late February or even late April. This is indicated in this area by the late winter departure of a large percent of the wintering birds -- juveniles and adults. The few thousands of adult eagles still occupying the southern BC rivers and coastline over the New Year only begin to really thin out in late January and February as they depart for their northern territories. The local birds are intensely into nest repair and even egg laying by the end of February. Of course those residents nesting near herring or oolachin spawning rivers have an extra feasting bonus. Others passing north to their nesting ground get to share this bonanza as of course do the juveniles who are not territory bound.
So back to our Sidney Ma and Pa. They have started another year for us to follow. Will this season provide the excitement and potential heartbreaks of last? Will this year again show that the Sidney pair are among the most productive of the North American bald eagles? Will they again be attacked at the site by other eagles about to visit the area to work the herring spawn of Patricia Bay -- their hunting grounds? Or will we again be privileged to witness a whole new set of insights? Our eagles never fail to excite me with new lessons -- and lessons to be re-learned.
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Best of luck to Sidney Ma & Pa -- their challenges are great.