Ospreys’ nesting effort draws competition atop maritime ship

The ospreys returned to Alameda Point again in 2013 to nest, but not at their previous nesting site on the old light stand at the entrance to the Seaplane Lagoon.  This year they settled atop one of the towering kingposts holding a cable and boom hoist on the maritime ship Admiral William Callaghan.  Unfortunately, a third osprey interfered with the nesting pair.

Osprey landing on the kingpost nest on the maritime ship Admiral Callaghan docked at Alameda Point - May 2013.
Osprey landing on the kingpost nest on the maritime ship Admiral Callaghan docked at Alameda Point – May 2013.

As the month of March came in, Alameda wildlife biologist and birdwatcher Leora Feeney began checking to see if the ospreys had returned to their Seaplane Lagoon nest.  While scoping out the surrounding area with her binoculars, Feeney spotted a returning osprey on one of the maritime ready reserve ships docked at Alameda Point.  As the weeks went by, she noted that nest building and fishing were the order of business for the osprey pair on their new shipboard nest.

Osprey bringing in nest material for the Callaghan kingpost nest - 2013.
Osprey bringing in nest material for the Callaghan kingpost nest, with mate in nest – 2013.

On April 4, Feeney recorded in her osprey log that the female had settled deep into the nest as if incubating at least one egg.  But a third osprey spotted two weeks earlier now became trouble, with the nesting male osprey seen escorting the interloper away.

“Incubation seemed the order of business during April, but on May 5th no birds were seen at the nest,” said Feeney.  “This was not a good sign.”  During following observations by Feeney, it became clear that another female osprey was visiting the pair often.  “The pair tried to discourage her by flying around her and escorting her away,” said Feeney.  But in doing so, the effort would leave the nest briefly unattended and vulnerable to the ever-present gulls looking to steal fish scraps or even an egg or a chick. 

The maritime ready reserve ship Admiral William Callaghan stationed at Alameda Point.  Arrow indicates nest location.  Viewed from Pier 3 next to USS Hornet.
The maritime ready reserve ship Admiral William Callaghan stationed at Alameda Point. Arrow indicates nest location. Viewed from Pier 3 next to USS Hornet.

“The female interloper, however, was persistent.  She appeared dirty, maybe oiled,” said Feeney.  “And it became questionable if the nest had eggs or chicks.  We were no longer seeing brooding,” said Feeney.

On May 20, the captain of the Callaghan generously agreed to allow a few interested parties to climb up to the bridge and higher to look down into the nest to gather more information.  No eggs or chicks were seen.  “But it didn’t help much to understand this year’s osprey story,” said Feeney.  “A strong theory is that the interloper disturbed the nesting pair more often than my brief visits detected,” she said.  “The other ‘woman’ may have allowed enough distraction for the active nest to be pirated by gulls.” 

It was hoped that a second nesting attempt might occur, but it didn’t.  “There is always concern about adequate food availability and sufficient experience when birds nest,” said Feeney.  “And now we see competition is part of the game.” 

No one can say for sure what caused the failure.  “It is interesting, however,” said Feeney, “that two ospreys were still seen standing at both the 2012 nesting site that fledged one healthy big osprey and the 2013 ship nesting site as recently as August 23.”  “This site tenacity gives us hope that they will return in 2014.”

Video of osprey attempting to mate again after earlier nesting effort was disrupted by a second female.

 

This story also appeared in the Alameda Sun.

Author: richard94501

My blog is Alameda Point Environmental Report covering environmental issues from wildlife to cleanup at the former Navy base in Alameda now called Alameda Point. Articles on my blog are frequently printed in the Alameda Sun newspaper. I also host a Twitter site and a Flickr photo site. I hope you find my stories and photos of interest. Richard Bangert Alameda, California

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