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Sunday, July 5, 2015

It Takes A Village

Bushtits are smaller than pine cones and lay eggs about the size of acorns. If your knowledge of bird nests was limited to robins and hummingbirds, you might reasonably assume that bushtits build a cup-shaped nest, two or three inches in diameter, but this is not the case.

Bushtits are not satisfied with the most common nest design or an average construction process. Plus, once the nest is complete it is not used by just one parent at a time. The whole family may sleep in the nest while the eggs are being incubated, per All About Birds.

The male, with solid dark eyes, weaves dried grass, twigs and other plant matter into the initial framework of the nest.

The female, with yellow irises, watches. Spider's silk provides additional strength and flexibility. A completed the nest will be three or four times longer than what we see here.

Unlike most birds, it is not just the male, or even just the mated pair that build the nest. At least three different bushtits were involved in this Foster Island nest building operation. A third bird is visible, though out of focus, in the lower right.

Sadly, when I returned to check on the progress of this particular nest, it was gone. I suspect one of the supporting branches fell and the construction crew relocated to a more stable job site.

Luckily, one month later, I happened upon a completed nest while taking a class at the University of Washington. Along with dried grass, spider's silk and twigs, a large quantity of moss was also incorporated into the nest. 

While I watched, an adult bird flew to an overhead branch and seized a mouthful of moss. Pull as it might the moss would not come loose. Finally, using all of its weight and beating the air with both wings the little bird pulled the moss free, and carried it back to the nest.

The completed nest was essentially a woven bag with an entry port near the top. Relative to the size of the birds the nest is huge. Bushtits are only about 3 inches in length, while the nest was nearly a foot long, and towards the bottom, nearly five inches in diameter. The extra space helps accommodate the family and friends who participate with the nesting process.

Both male…

...and female birds were seen coming and going from the nest. Birds of North America Online provides information from Sarah A. Sloane* which says, "Flocks of 10-40 individuals can have many simultaneous nests, each attended by 2-6 individuals." The ability of bushtits to work in groups to build nests, incubate the young and to live peacefully is truly impressive. 

It is interesting to compare the bushtit reproductive process with an Anna's hummingbird. Both types of birds weigh about the same, but their approach to nesting and incubation is totally different. The female hummingbird builds the nest, incubates the eggs and then feeds the young virtually alone, while the female bushtit may be one of a half dozen birds carrying out the same activities. 

We can see the result of the different approaches in their average clutch sizes. Anna's hummingbirds generally have only two eggs in a clutch, while All About Birds says that bushtits have from four to ten eggs in a clutch, which implies an average of seven. Evidently, many beaks makes the work light.

With bushtits, it take a village to raise their young, plus a crew of engineers to build their nests.

Have a great day on Union Bay…were bushtits nest in the city!

Larry

PS: You can see more about the socially advanced bushtits in the Feb. post, Sex in The City

Sloane, Sarah A. 2001. Bushtit (Psaltriparus minimus), 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/bna/species/598





2 comments:

  1. Thank you for this detailed post about one of my favorite birds. We have a bushtit nest in our yard this year--we thought it had been abandoned but it seems that the crafty bushtits were just very quiet after construction was complete. We theorize they're working on a second clutch now (is that likely?) as the nest is periodically full of cheeping with adult birds flying in with food.

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    1. How exciting! Yes, I have read that sometimes they have a second clutch. With all the delayed activity a second clutch seems most likely. :-)

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