Have you ever come across a peculiar nest that sheltering blue eggs inside? Blue bird eggs are real wonders of the natural world. In the UK alone there are more than five common species of birds that lay blue eggs in their nest. While Dunnocks, Blackbirds, Song Thrushes, or Starlings are the most common species in this country, the world has many other birds with beautiful blue eggs.
Although you may know that bluebirds usually lay blue eggs, you are not likely to discover these eggs yourself. In North America, in mountainous areas, bluebirds lay pale blue eggs which are rarely seen by humans. Bluebirds are cavity nesters which rarely lay their eggs outside the cavity; the only exception is when they are desperate. There are about 4-5% of bluebirds that will lay white eggs.
However, there are hundreds of different birds capable of laying blue eggs, and many can be found in human-populated areas.
If you come across a nest with blue eggs, experts ask people to avoid disturbing the eggs and the nest overall. It is against the law in some countries to take eggs or to purposefully investigate a nest. There are even laws punishing this action.
Today’s little guide will tell you everything about the species of birds which lay blue eggs and their particularities. Size and markings can be a good indicator of which eggs belong to which species, and this guide will help you identify blue eggs.
Some Birds Which Lay Blue Eggs
Most people would probably expect only the bluebirds to lay blue eggs. However, this is only partially true, as you will discover below.
There are hundreds of bird species that have these particular and cute blue eggs, so let’s learn more about them…
The American Robin will usually lay clutches of between 3 and 5 light blue- or sky blue-colored eggs. These blue eggs are between 2.8cm and 3cm in length, while their width will be around 2cm.
Some of the most common blackbirds, the Eurasian blackbirds, will lay their blue eggs from March to July. These birds will lay somewhere between 3 and 5 eggs at a time.
The eggs have a blue-ish green shade, with distinctive red speckles. The average dimensions of Blackbird eggs are 22mm in width and a length of 29mm.
Song Thrushes lay a clutch of 4 or 5 glossy, light-blue eggs with purple and black spots. These eggs are tiny, around 21mm in width and 27mm in length.
Dunnocks are sometimes confused with another similar species, the House Sparrow. Females lay a clutch of around 4 or 5 eggs.
These blue eggs are glossy, smooth, and come with some reddish spots. The eggs are approximately 14mm wide and have a length of 19mm. Pretty tiny!
Dunnocks are beautiful birds that don’t breed in pairs but in groups. The groups can consist of up to three males and three females, but there will be only 2 of each gender most of the time.
The nest is built by females, and constructed with materials from hedges and shrubs. The nest is cup-shaped and is lined with animal hair and moss.
Starlings are dark, patterned species with fantastic iridescent plumage when you look at them closely. They lay a clutch of around 2 to 9 eggs. During the first several days, the eggs turn from white to green or pale blue.
Magpies are common birds across the whole UK. The eggs of Magpies are similar to Blackbirds’. As such, they look bluish-green and have some speckles.
However, they are a bit bigger than blackbird eggs, with a width of around 24mm and 35mm.
House Finches lay eggs that have a bluish-green color, with some speckles. Sometimes, the birds will use nest boxes and lay up to 4 or 5 eggs.
The ideal period of laying eggs is between late March to late July depending on the location. The dimensions of these eggs are between 1.6 to 2.1 cm with a width between 1.3 to 1.5 cm.
Now that we have described the most common birds with blue eggs, we’ll briefly mention some other, more unusual species which lay blue eggs:
- Gray Catbird
- Red-Winged, Tricolored, or Rusty Blackbirds
- Blue Mockingbird
- Blue-footed Booby
- Gray Catbirds
- American, Tamaulipas, or Hawaiian Crow
- Blue Jays
- Common Myna
- Cassin’s Finch, Oriental Greenfinch
- Snowy Egret
- Little Blue Heron, Great Blue Heron
- Eastern, Western, and Mountain Bluebirds
- Eurasian Jackdaw
Main Reasons Why Birds Lay Blue Eggs
The bird’s anatomy is impressive. The female birds have two “ink cartridges” placed in their reproductive system: protoporphyrin and biliverdin. All birds possess these two molecules, but this does not necessarily mean that their eggs will turn out blue.
What makes the eggs blue is biliverdin, a molecule that produces green pigment in eggshells. The higher the concentration of biliverdin, the bluer the egg.
On the other hand, protoporphyrin is the pigment that will make the eggs brown or red or create visible patches and speckles all over the eggshells. These types of pigments will be added to the new shell during the last few hours of egg production.
What is even more interesting is that the color of the egg will change throughout egg development. Often, as each egg is laid, it will be paler in color compared to the egg before it. The reason for this is that the female bird may begin to run out of nutrients, and in particular calcium.
Considering that 10% of the calcium in eggshells comes directly from the system of the mother birds, they need to take some extra nutrients while laying eggs. If they cannot procure the nutrients they need, the eggs will vary in color. So why this particular blue shade necessary or useful for birds?
As you might already know, lots of animals from the wild kingdom are colored or patterned so they can blend with the environment they live in, helping them to evade predators.
In this way, fragile eggs will be safe from possible enemies. Considering many hungry predators consider bird eggs as a nutritious meal, camouflage is required.
Unfortunately, that camouflage is not that successful when it comes to blue eggs, as the shells do not blend into the nesting material. However, mother birds may add a layer of protection by placing nest material over the eggs to keep their blue eggs safe.
Blue eggs are pretty peculiar and unique to see. If you are lucky enough to notice some blue eggshells, make sure you won’t disturb the winged animals but only admire the beauty of Mother Nature.