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Old 06-16-2011, 07:22 AM   #34
linrose
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Join Date: Feb 2010
Location: Kentucky
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If it makes anybody feel any better, according to Sialis.org - For Eastern Bluebirds, about 55-84% of nesting attempts fail (Radunzel et al 1997.)
I'm pretty sure house wrens did in my last brood on top of the hill because it was too near house wren habitat. I've since removed the box and placed it further away from wooded edges and very far away from where it was. However I'm not certain is was definitely house wrens. We did find a wasp nest starting inside the predator guard we made for the pole. They could have caused the parents to abandon the nest. It would be ironic that a predator guard caused the problem instead of solving it.

The good news is that there are 5 new eggs in the box nearest the house that has had a 100% success rate since we installed the predator guards making it the second brood of the season.

I've never tried a wren guard but it may be useful, timing is crucial for their success which requires daily monitoring. It has to be placed after the first egg is laid but before the last one. Also if house wrens have attacked that box before it is less successful.

This is the Sialis page on house wrens for more info.
House Wrens - discouraging, wren guards
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