Ask SIB: Eastern Bluebird Winter Behavior

On January 9, 2021, Andy wrote SIB, “Today we saw maybe half dozen blue birds and one was sitting on the entry hole.  Isn’t it early for them to be nesting?  Has the warm weather put them off schedule?”

Eastern Bluebird – photo by Bob Mercer

The questions are relatively easy to answer. Yes, it is too early for them to be nesting, so they are not “off schedule” due to the weather. As usual, the questions lead to another question; what are the birds doing?

Since Eastern Bluebirds are year-round residents in our area, one can watch the full range of behaviors. During the winter months, bluebirds can gather in flocks of up to 20 birds. These flocks consist of one or more family units. In really cold weather, a flock of bluebirds may all cram into a single cavity, presumably for shared body warmth. Pair bonding for bluebirds can happen anytime between November and March.

This photo of an Eastern Bluebird entering the box and the female watching perfectly captures some of the courtship behavior–wing droop tail spread. Photo by Nancy Brown

During the courtship and nesting period, the flocking behavior disappears. Once a pair settles on a territory, they work hard to drive away all competitors including their siblings. 

It is difficult to know exactly what Andy observed, but one can make an educated guess. Since he saw a half dozen birds, he observed a winter flock. The bird sitting at the nesting hole most likely was a male bird checking out the box for its potential. 

Once a male makes a choice, he will then attempt to attract a mate or to solidify his relationship with his current mate. According to the Cornel Lab of Ornithology website Birds of the World, the male goes through a very predictable pattern of behavior. The male institutes a nesting demonstration display where he perches at a hole holding nesting material with his wings drooping and his tail spread wide. He looks around, presumably to make sure his intended is paying attention, and then look in the hole. The next step is to rock back and forth into and out of the hole before going in the cavity. Once in the cavity, he will stick his head out still holding the nesting material. Leaving the material in the cavity, he then hops out near the hole and does a wing waving display. The female entering the box cements the pair bond. 

People with bluebird boxes they can view, or who have cameras trained on a box, may be lucky enough to watch this behavioral sequence. 

Nesting on Seabrook Island usually begins around the first of March. The Seabrook Island Birders sponsor a bluebird box monitoring program. Volunteers have a route where they check a series of boxes once a week to monitor if birds use the boxes and nesting success of failure. Anyone interested in helping is encouraged to contact the Seabrook Island Birders.

Be sure to read tomorrow’s article discussing the installation and monitoring of a birdhouse with an outside WIFI camera!

Gowaty, P. A. and J. H. Plissner (2020). Eastern Bluebird (Sialia sialis), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.easblu.01

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