Harrison Mills Eaglets - doing fine in spite of size difference


Written on June 2, 2013.


A four day differential in hatching dates is an invitation to a "survival of the fittest" challenge going the way of the bully but so far our HM chicks seem to be coping.  At 9:44 AM, June 2, both chicks are peppy and with half full crops.  The parents are apparently doing a good job providing food.   Oops -- as I write, 9:50 AM, big chick head pounds the little one who instantly turns away to lessen the beating.  This of course, the turning the other cheek,  is the successful way to thwart fratricide.  However, the other side of that issue is that when the big sibling is full, there still must be enough food to keep the little one growing and healthy.  You would also like to think the little one would catch up but this surely does not seem to be happening here -- at least not yet.  At 10:00 AM the big one again pounded the little one -- and yet they both have 1/2 full crops.


From the first couple of days the size differential of the two chicks seemed to be expanding -- and this has continued.  On the other side, the little one has learned the "turn away response very effectively" and has been getting enough food to keep vibrant, active and apparently healthy. Now at 23 and 19 days of age the size difference is quite exceptional considering there were only two eggs - though they were laid four days apart.  'Perky' seems to be the desired behavior and the little one seems to foil attacks effectively and come back strong -- but smaller in proportion -- each day.  My guess is that if enough food is delivered we will see both chicks fledge.  If not then the system has done presumably what it was supposed to do -- at least produce 1 chick under poor food availability rather than let both starve.

I have no real insight into the two chicks' gender. The obvious difference in size suggests that one might be a small male and the other a larger female.   This is probably the case but we could also, as some of you have observed, be seeing the accentuated growth of the bully well over the stunted growth of the late chick -- regardless of or exaggerated by innate gender size expectations.  By fledging time the chicks should be to full size and the gender differences more normal.  To my understanding there is no data to suggest that the first hatched is predominantly one gender or the other.

At some point I have probably pointed out that in most raptors the smaller male actually develops it final body and flight feathers 2 to 4 days before the female -- or at least catches up with a larger female at the last stages of feather growth.  This data is more from observations of hundreds of captive bred raptors raised side-by-side. This presumably lets the smaller male catch up and participate in fledging activities -- flight and hunting training for some species.  The interesting question is, 'Can such a smaller late developing sibling ever catch up to its full potential size by fledging time?'  Or will it remain a runt?  I think it will catch up to its potential size.

The Harrison Mills adult pair and the chicks have been a marvelous study.  As some of you know, I had already written off the productivity of this territory for 2013 since we had so little adult activity at the site from October through February.  When I had installed the two cams back in September, 2012 I had been elated to find a dead chick in the nest. That was my first confirmation that the site had been occupied since seeing adults on site in April, 2012.  

We had some early winter excitement with the toeless eagle in attendance a few nights, visits by a couple of other adult birds but nobody showing regularity or staying power.  Then these adults came along late, went through intensive but brief nest building, laid eggs and followed through with incredible discipline of incubation, brooding and now feeding the young.  

I believe this is a new pair that took up residency, showing up on March 10, 2013 and laying the first egg April 4.  They seem a well experienced pair.  They are certainly doing well and if the river and fields produce the food we could easily see the pair fledge both chicks.  The pair directly eastward across the Harrison River beside the Old Orchard Campsite now have two big chicks -- their usual. 

To me the really interesting question about this pair is "Where did they come from?"  How or where did they seem to acquire all the professional experience to do so many things right?  When you compare the inadequate behaviors at the White Rock nest, with all the different birds attempting to nest this year that resulted in total failure, this late arriving pair seems to have it all together.  How?  Did they come from another nest nearby?  This is actually more possible that you might have thought. 

About two miles north of this nest is the famous Morris Valley Slough and this area has been part of my study.  It is just on the northern side of the Sts'ailes village - the Harrison Mills nest is on the southern side.  The Morris Valley nest, overseeing this very famous and rich Morris Valley Slough had a pair of eagles nesting on the eastern shoreline.  By the way you can see one nest from the other across the Chehalis alluvial fan. This nest was directly in line with the newly advancing BC Hydro power line and the nest was removed.  I was actually brought in to consult on the mitigation.  What could be done in return for removal of the nest?  Well the answer was quite simple in my mind.  First considerations were given to the rare and endangered frogs in the slough.  Then there were lots of adjacent very large trees that could support a bald eagle nest.  The 'removal permit' had requested Hydro to improve two or three alternative but nearby trees.  I simply advised the climbing crew what nearby trees to place crossbars and take out a couple of "flight blocking branches" to facilitate a new nest. The real challenge here was that the nest removal and work up in the new trees was done in late January when the eagles were already on territory.  Then with the huge helicopters, the many work crews and researchers using this same site I doubted we could expect the eagles to establish a new nest this season.

Perhaps this pair decided to simply move downstream two miles and take advantage of the unoccupied HM site. I personally suspect this is the case and the Harrison Mill nest site and territory was literally the immediate territory to the south and they took advantage of it. Six years ago there was another nesting territory between the Morris Valley nest and what is now our Harrison Mills nest.  However, that nest tree on the Sts'ailse village site, was in a tree that fell. This meant that the Morris Valley pair held the adjacent territory making the move even less a shift.   If the experienced Morris Valley pair are indeed our pair it certainly explains why they arrived on the scene late - when they were driven off their territory in February by continuing human activity - and why they had so much parental experience.

I was back once to see if the Morris Valley pair was there but I could not see them  I will follow up on this shortly.  In the meantime our pair of HM chicks are giving us some marvelous further insight into the eagles' ways.  The Harrison River has been defined as Canada's first Salmon Stronghold river because it produces so many fish. Let's hope our HM pair benefit adequately to rear both young.

David Hancock
 

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