Did you ever wonder why some birds, such as Bluebirds and Robins, lay blue or bluish green eggs? And just as interesting why, in some cases, Bluebirds which generally lay blue eggs, a nest may comprise eggs that are almost white?
The earliest avian eggshells probably lacked color, or pigmentation. Over time, most likely to protect the eggs from predators, birds evolved a diverse range of colored shell markings from mottled brown, gray and beige to rainbow hues from pure white to pale pink, lavender, yellow, aqua, orange, blue, born and even black.
The molecules that cause pigmentation in bird eggs are biliverdin (the blue-green shades) and protoporphyrin (red and brown colors and speckles) but we can talk about blue eggs without getting too technical.
Basically, blue and blue-green strikes a balance between white and very dark colored eggs. Darker eggs are predicted in moderate light to shield the embryo from intense light, including harmful UV radiation. If when eggs are in an exposed nest and the shells are too dark, it can cause the interior to heat up, similar to a “dark car effect.” Simply stated, blue eggs regulate the effects of sunlight on the developing chick (embryo).
This doesn’t explain entirely why Eastern Bluebird eggs range from white to blue green. Many cavity nester’s eggs are white because the adults need to see the eggs in the dark. Wood Ducks are an example of cavity nesters with white eggs. American Robins generally nest in trees or a semi-exposed site and their eggs are blue, affording both protection from dangerous UV light and low risk from heating up. Eastern Bluebirds are cavity nesters but only about 4 to 5 percent of their eggs are white. Oftentimes when learning about a topic, myriad more questions come to mind!
In reading about blue eggs I thought readers would enjoy seeing the amazing speckled and pear-shaped brilliant blue egg of the Common Murre, from USFWS
Some birds with blue eggs that nest locally include Red-winged Blackbird, Gray Catbird, Snowy Egret, Great Blue Heron, Little Blue Heron, House Finch, Bluejay, Goldfinch, European Starling, Eastern Bluebird, and American Robin.
American Robin nest at a friend’s home
Both Bluebird nest egg photos courtesy Google image search
Happy Spring, Happy Easter dear Friends. To new beginnings for us all as the pandemic hopefully soon recedes. Sending much love and appreciation for your kind comments and friendship throughout the year.
“Hope” is the thing with feathers –
That perches in the soul –
And sings the tune without the words –
And never stops – at all –
And sweetest – in the Gale – is heard –
And sore must be the storm –
That could abash the little Bird
That kept so many warm –
I’ve heard it in the chillest land –
And on the strangest Sea –
Yet – never – in Extremity,
It asked a crumb – of me.
Bluebird courtship is as beautiful as is the bird! Last week my daughter Liv joined me on a film scouting mini adventure. She loves learning about wildlife and living in Southern California as she does, Liv is surrounded by beautiful wild creatures and wild lands. We had a fantastic morning of it. Brant Geese, Piping Plovers, Great Egrets, Tree Swallows, and Eastern Bluebirds were just some of the creatures we observed.
The Eastern Bluebirds were especially stunning in the crisp early morning sunshine. One particular gent had not yet secured his partner’s affections. From tree branches adjacent to nesting boxes, he sang softly and flashed his glorious blue wings to a female that had flown in on the scene.
At first we thought he was preening, but no, the bachelor was clearly enticing his lady friend with lapis lazuli flags, gesturing with quick up and down lifting movements. Called wing-waving, these gestures are part of Eastern Bluebird courtship.
The male first sings loudly from treetops. If a female shows interest, he further shows off his skill sets with wing-waving and soft warbles. He then entices her to join him at a nesting box or cavity, he entering first. After he flies out of the box and if all goes well, she enters the cavity, a sure sign the pair are hitting it off!
Consistently when out in fields, I see Bluebird pairs that appear strongly committed to each other. I wondered, do Bluebirds mate forever? In our region, we see Eastern Bluebirds. Ornithologists found from a long term study of Western Bluebirds that the great majority stay together for life. No such studies exist for Eastern Bluebirds however, field observations suggest that about 95 percent mate for life when both are still alive.
Eastern Bluebird female, left, male, right
Interestingly though, mating for life does not exclude extra pair copulations. Genetic studies of broods show that about twenty percent of nestlings are sired by more than one male.
Pairs softly warble to each other early in the morning, the male brings nesting material to a chosen site, and once she has entered his nesting cavity, she will begin to bring nesting material and he will bring food to her to “seal the deal.” In our north of Boston region, you can see the courtship behavior beginning as early as February and March.
Eastern Bluebirds re-mate with another partner if one dies.
In the photos below, it’s very easy to see the difference between a male and female Bluebird. The female’s blue is a more subdued grayish hue while the male’s blue feathers are brilliantly hued.
The very last thing I expected to see on this morning’s trek were Bluebirds. So many shades of blue in those beautiful wings – Egyptian Blue, Azure, Cerulean, Lapis lazuli, Coblat, Ultramarine -simply astounding! More to come when I have time to sort through photos this weekend 🙂 Eastern Bluebird Male
The male Eastern Bluebird shows a brilliant indigo blue on the head and back, with a rusty reddish brown breast. The female is more softly colored overall, with elegant gray wings, tinged in shades of blue, and paler breast. Joe Ciaramitaro photo
Eastern Bluebird (Sialia sialis)
Several days ago my friend Joe from Good Morning Gloucester blog captured (with camera) a pair of Eastern Bluebirds. Everyone who responded in the comment section spoke so fondly of this beautiful bird that I thought we’d all enjoy knowing a bit more about its current status in Massachusetts. And too, sightings at this time of year give reason to share a favorite Emily Dickinson poem—“Before you thought of spring, except as a surmise…”
Before you thought of spring,
Except as a surmise,
You see, God bless his suddenness,
A fellow in the skies
Of independent hues,
A little weather-worn,
Of indigo and brown.
With specimens of song,
As if for you to choose,
Discretion in the interval,
With gay delays he goes
To some superior tree
Without a single leaf,
And shouts for joy to nobody
But his seraphic self!
Bluebirds do indeed appear to sing with great joy from the treetops, and reading this poem always makes me smile, thinking about “a fellow in the skies” singing to nobody but his rapt self. As is so typical of her work, Emily Dickinson’s poem is an astute and honest observation of the natural world, but I also interpret her poem to mean that joy is an emotion that doesn’t need an audience; that it can be expressed for the sake of joy itself.
Eastern Bluebirds sing several types of songs; one is a liquid birdsong—sort of a turee song—and another is a soft melodious warble. When trying to attract a mate, unpaired males typically sing from a high perch, and sometimes even in flight. Both male and female sing in all seasons to keep in touch with each other and to signal to nestlings that food is on its way. Bluebirds are in the Thrush Family, as are American Robins, and Robins too sing a lovely liquid birdsong.
From the Mass Audubon State of Birds:
“The very widespread breeding distribution seen in the Eastern Bluebird in Massachusetts today is, in large part, the result of considerable support received by concerned citizens who, for more than half a century, erected large numbers of nest boxes across the state and helped save the species from near-extirpation.”
What does “extirpation” mean? Not that a species has become extinct from our planet, but that it is no longer found in a particular area. We are very fortunate that the Eastern Bluebird did not become extirpated from our region. Bluebirds are cavity nesters and use suitable bird boxes, tree cavities, and old woodpecker holes in trees and fence posts to build their nests. During the era when settlers cleared forests and planted fields and orchards, the Eastern Bluebird became quite common. In the 20th century their population decreased by nearly 90 percent for several reasons, two of which are because vast areas of New England have reverted to forest, and because the bluebird is competing for nesting sites with the alien European House Sparrow and European Starling. The return of the Eastern Bluebird during the spring and summer breeding period is due in large measure to citizens throughout the state building and placing nest boxes along “bluebird trails.”
Eastern Bluebird and Winterberry
If you are fortunate enough to have bluebirds visiting your backyard, you may want to provide them with supplemental food. Bluebirds are primarily insectivores. They do not visit bird feeders because their bills are not designed for cracking open seed and nut shells (but they will eat hulled sunflower seeds). They eat berries at this time of year because there aren’t any insects. The winterberries won’t last long on the bush with flocks of hungry birds descending to your garden. Mealworms (which aren’t really worms at all, but are the larval form of the darling beetle) are the most nutritious supplement you can provide bluebirds. For more information on feeding mealworms to bluebirds go to this fact sheet: North American Bluebird Society’s Mealworms Fact Sheet.
For a wonderful FREE downloadable 15 page education packet designed for grades 1-5, with coloring pages and puzzles follow this link: Education Packet
For more information on how to build, and where to site, bluebird nest boxes, along with plan drawings, follow this link: Getting Started with Bluebirds
To read more about the devastating effects of European House Sparrows and European Starlings follow this link: House Sparrow Control.
Just this past week, 15 Eastern Bluebirds were spotted at Allens Neck Wildlife Sanctuary in Westport, Massachusetts. See Bluebird Nestbox Walk at Allens Neck post for information about an upcoming.