Friday, May 21, 2010

Eastern Bluebird 2

I banded an adult Eastern Bluebird today.  J.H. has noted some mortality among his bluebirds during this cool, wet May and we have heard similar reports from other Minnesota bluebird trail owners.  In recent years, more bluebirds have fledged in our county (Rice) than any other in the United States.  This factoid could be due to there being more bluebird enthusiasts maintaining boxes here than elsewhere.

As I took the bird from the net, its mate attacked me.  I was disappointed that the male was not one of the young banded during the past couple of years.  I should not have been surprised, since adult males, after wintering with their young, aggressively chase them away during the next breeding season.  (Males will fight over mates or territories, as will females; indeed these fights can result in the death of one of the combatants!)

As is the case with many well-studied species, bluebird breeding behavior can be complicated.  Although pairs are often monogamous, males can be polygamous.  Females can be in separate cavities in the same territories or the male may have more than one territory, each with a female.  Also reported are records of one male with two females in the same nest box!  Polyandry is also known, where one female nests with more than one male.  About 20% of bluebird houses contain young not fathered by the "owner" of that box. Finally, the young of first broods occasionally help their parents feed the young of second broods. 

The source for most of this information is: Gowaty, Patricia Adair and Jonathan H. Plissner. 1998. Eastern Bluebird (Sialia sialis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/381

2 comments:

  1. Dan,
    I had a pair of Eastern bluebirds investigating one of my birdhouses late this afternoon. They are the first Easterns that I have seen in 5 years here. The Mt. bluebird pair have claimed a box on the other side of the yard. Don't know if they will stay, they were disputing possession of box with pair of chickadees. Pleased to see them if only briefly.
    Caroline Stafford
    44N 103W (sw Rapid City)

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  2. Interesting information about the Eastern Bluebird. I'm always learning something new. Thanks. I build an Eastern Bluebird house. You can see it at http://www.myadirondakchair.com

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