Monday, May 08, 2006

Hornby Island eagles

I hadn't checked the website for quite awhile, so I was suprised and saddened by the news:
The eagles nesting at Hornby Island in British Columbia have had a total nest failure:
Sunday, April 30 2006 @ 03:09 PM PDTContributed by: davidhViews: 214042

Sad News:
April 30, 2006
Eagles and conservation have been the joy and occasional sadness of my life. This is a sad moment. It appears that the Hornby Island bald eagle eggs are infertile. The first egg should have hatched April the 26 and the second egg today. The first embryo, if it developed at all, is surely dead. The second embryo, could still hatch but I cannot see the proper pipping of the egg shell, where the chicks beak has broken through enabling it to draw in air, the precursor to the final struggle for hatching. It does not look good for this pair this year. In fact this is the second year of failure for this nest territory.
Reasons for the Failure to Hatch:
We cannot be sure. Some educated guesses follow.
The adult eagles are possibly old:
1. This is the 19th year for known nesting results from this tree. It could have been occupied for 50 or more years earlier. Was the same pair occupying the nest all that time? We do not know. Eagles could live that long.
2. If the birds are very old it is possible that they have simply run out of reproductive ability. Perhaps they simply can’t produce viable eggs any longer.
3. Alternatively, it is possible with very old birds that they have accumulated so many pesticides and heavy metals that their reproductive track is no longer able to function properly. This is not at all out of the question. I am told that orcas (killer whales) that now periodically die along the British Columbia and Washington coasts are so polluted and their bodies so loaded with poisons that it is illegal to tow their bodies out to sea or have them hauled to land fills. They carcasses have to be burned. A very sad statement on our polluted earth. Are these eagles, who also occupy the top of the food chain and eat the same basic foods as orcas, also contaminated. Very possibly. Maybe the reproductive success is going to be restricted to younger eagles that have not had so long to accumulated the poisons.
One or more of the adult eagles is young and inexperienced:
1. This is possible – but not liklely. Last year when the territory only hatched one young which died at 6 days of age and the other egg did not hatch, both adults were in full adult plumage – not even just newly matured at 5 years as this would have been indicated by the dark streaking in their white head or dark tail band. These birds appear to be fully mature both last year and this year. Furthermore, this pair appear to e very experienced in nest building that we got to witness in such marvelous detail, and in fullfulling the incubating duties. They hardly left the eggs unattended more than 12 to 40 seconds during any exchange that I witnessed. They are not just good, and I assume experienced parents, but so compatible with each other. I take this beautiful pair to be very experienced parents. So the loss again this year of their eggs I also view as most likely due to loss of fertility due to age or polution.
Other alternatives:
There are infinite options but none seem logical than my first option above. The pair are very used to human disturbance, constantly perching near houses and human activity with no noticeable alarm or concern. While I have received lots of concerned calls and emails at the sounds of power movers, cars, chain saws and dogs we have had an unprecedented opportunity to watch the eagles in the cam and correlate their behavior with disturbances. The noise of civilizations does not seem to phase them a bit.
I found one call from an irate and annoyed caller quite interesting. She heard the disturbance of barking dogs and instantly called me. I was actually calling Doug to question him about this. After many rings he answered the phone and reported that he delayed coming in to the phone until the herd of barking sea lions has passed by his porch. I hardly think barking sea lions would be a disturbance to bald eagles – and indeed barking dogs elicit no interest from the nesting birds either.
Eagles like most creatures in the wild are constantly subjected to the test of survival. Can they find food and make a living? Can they avoid being killed and eaten. Can they avoid hurting and damaging themselves? If they can’t keep their feathers in good condition they won’t be able to fly efficiently and hunt effectively and they will die.
Almost half of the eagles that start nesting loose their eggs or young. Surviving in the wild is not easy. Of those young that survive to fledging only a small percentage are likely to survive the five years to maturity. Once they have proven themselves as good hunters and they enter the breeding population they can produce young for 15 to 25 or more years. Now pause for a moment to contemplate how many eagle there would or could be it the adults were successful lin raising one or two young every year for 20 years! That could be that each pair produced 30 or 40 young – far more than necessary to keep the population stable. And stable would mean producing a new eagle for every one that died.
Therefore, with such a long live potential, their has to be a lot of nest failures or early deaths otherwise the world would be full of eagles – and no room for any other species. Not a balanced system.
So as much as I was very saddened to not see our beautiful pair of adult bald eagles produce eagles this year it is not an unexpected happening that they should fail. If, as I suspect, these are old eagles, they have already produced many replacements for themselves and they have been great contributors to the very successful and expanding eagle population that we have been experiencing the past 50 years. It is not a good thought that they have stopped reproducing because they have become sterile from pollution and this is also not confirmed.
We will hope and expect that other eagles will be more successful and they their young will be flying over our waters. If our adult pair is at the end of its reproductive life we can anticipate younger birds moving into the territory shortly and becoming the parents of the next generations.
David Hancock

1 comment:

Endment said...

Wow this is too bad -