Santa Cruz Island Bald Eagles: Unhappy Endings

The 2009 nesting season for bald eagle parents K-10 and K-26 came to an early and unfortunate end in mid-April, when the pair’s two chicks failed to survive more than a few days after hatching. Loyal eagle cam viewers, who have observed the nest activities on a daily basis, are undoubtedly saddened by the recent events, and questions have been pouring in to the Ventura County Office of Education’s bald eagle cam discussion board.

Peter Sharpe — wildlife biologist with the Institute for Wildlife Studies and director of the Channel Island’s bald eagle restoration program — responds to questions and talks about the bald eagle restoration program, the failure of the Pelican Harbor nest and what the future potentially holds for parents K-10 and K-26.  

Peter Sharpe is a wildlife biologist with the Institute for Wildlife Studies (IWS). Since 1997 he has directed the Institute’s bald eagle restoration project on California’s Channel Islands. Known as “the eagle guy,” Dr. Sharpe has been featured on Animal Planet, in People magazine and in the IMAX movie Adventures in Wild California for his expertise in fostering eagles, which sometimes requires him to hang from a helicopter in order to access hard-to-reach nests. He holds a BS in ecology and ethology, an MS in zoology and a PhD in zoology.

What is the goal of the northern Channel Islands bald eagle restoration program?

Peter Sharpe:

In 2002, we began a study on the reintroduction of bald eagles on the northern Channel Islands, including Santa Cruz Island. The study was to determine if bald eagles could be successfully restored and thrive in the wild without human intervention. On Santa Cruz Island, we haven’t manipulated the nests (removing eggs, fostering chicks), as we have done in the past on Catalina.

In 2006, we had the first two wild-born chicks on Santa Cruz Island to hatch anywhere on the Channel Islands in more than 50 years.

What was the cause of the Pelican Harbor chicks’ deaths?

Peter Sharpe:

There is really no definitive way to know what caused their deaths, or if it was the same cause. There are a multitude of possible reasons; many depending on the age of the chick and how many chicks are present. Young chicks can die of infections, sibling rivalry, starvation and accidents. Although we don’t know for sure, we don’t think they died of starvation because they were only three days old. Sometimes young chicks just fail to thrive.

Will you perform necropsies on either of the Pelican Harbor chicks?

Peter Sharpe:

No necropsies of these chicks are planned. Necropsy rarely determines the cause of death for our birds, unless they died of obvious causes, such as a bird with a fishing lure in its mouth, or fishing line wrapped around its wing. Necropsies are most useful for determining human-caused mortalities, such as shooting (bullet fragments seen in X-rays) or electrocution (burns, etc.).

What are the survival rates for eggs and chicks in the wild?

Peter Sharpe:

Probably about 80 percent of fertile eggs will hatch. Only about 50 percent of bald eagle chicks will survive until they are a year old, and most of that mortality occurs after fledging.

How soon after the failure of a nest and the loss of chicks do parents actually abandon their nest?

Peter Sharpe:

It depends on what stage of reproduction the chicks are in when they fail, and it will vary from pair to pair and from territory to territory. It can be less than a couple of weeks, unless they decide to try again to reproduce.

Is there a chance that K-26 and K-10 will have another clutch this year?

Peter Sharpe:

I've not had any eagle lay a second clutch after sitting on the first one to hatching, but anything is possible.

What is the success rate for fledging on the Channel Islands?

Peter Sharpe:

In general, about 80 percent of eagles that hatch will fledge. We have a 99 percent fledging success from our hack towers. ("Hack towers" are large nesting boxes about ten feet off the ground, where the birds can test their wings and adjust to the island's breezes.)

For the northern Channel Islands, nearly 70 percent of the bald eagle chicks survive to one year, around 63 percent to two years, and approximately 60 percent up to three years ? so we do have a higher survival rate than populations seen in more human-disturbed areas.



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