how big are bird eggs

Colors edit Guillemot eggs

While some birds, primarily passerines, produce colored eggs, vertebrate eggs are typically the default white color of the calcium carbonate from which the shells are formed. Protoporphyrin produces reds and browns as a ground color or as spotting, while biliverdin and its zinc chelate give a green or blue color. Except for certain ground-nesting species like the Charadriiformes, sandgrouse, and nightjars, where camouflage is required, and certain parasitic cuckoos, whose eggs frequently resemble those of their passerine hosts, non-passerines usually lay white eggs. In an attempt to reject cuckoos’ fake eggs, host passerine species have combined their ability to recognize visual patterns with other egg markings, such as blotches and speckles, to varied degrees of success [2]. In contrast, the majority of other passerines lay colored eggs, even though cryptic colors are not necessary. [3].

Nonetheless, it has been proposed that the photographic markings on passerine eggs serve as a solid state lubricant, thereby lessening brittleness. [4] The egg shell may be thin if there is not enough calcium in the surrounding soil, particularly in the area encircling the broad end. Protoporphyrin speckling makes up for this and rises in direct proportion to soil calcium levels. [5] Quantifying this pigmentation is crucial to comprehending the functional significance of eggshell spotting, also known as maculation [6]. For the same reason, later eggs in a clutch have more spots than early ones because the female’s calcium reserves are being used up.

Birds that nest in trees typically lay blue or greenish eggs, which can be speckled or not. On the other hand, birds that nest in bushes or close to the ground are more likely to lay speckled eggs. Individual egg color is also genetically determined, and it seems to be passed down exclusively through the mother. This suggests that the pigmentation-causing gene is located on the female-specific W chromosome (male birds are ZZ, females WZ). Previously, it was believed that color was applied to the shell right before laying, but new research demonstrates that coloration is a necessary component of the shell’s development and is caused by the same protein that deposits protoporphyrins in the absence of calcium carbonate. [7].

The distinctive markings on the eggs of species like the common guillemot, which nest in large groups, enable the females to more easily recognize their own eggs on the crowded cliff ledges where they breed. [8].

Shape edit

The shape of eggs varies greatly amongst bird species; the common murre’s eggs are highly pyriform or conical, while the little bee-eater’s eggs are nearly spherical. The chicken egg’s shape lies in between. Early egg shape scientists[10] hypothesized that peristalsis forces the egg through the oviduct, giving eggs their oval shape. According to this widely accepted [11][12][13] but false theory of how the shape of an egg is formed, the spherical egg membrane slightly distorts into an ovoid shape, with the blunt end caudal (i.e., caused by the contraction and relaxation of the muscles that push the egg down the oviduct). e. furthest down the oviduct and closest to the cloaca). The egg is laid with the blunt end visible first because of the way the uterus and shell gland calcify the egg, maintaining its shape (see this diagram for a breakdown of the various parts of the bird oviduct). Nevertheless, studies of egg shell formation in several bird species using methods like X-ray photography have disproved this theory, showing that the shape of the egg is determined in the oviduct isthmus (prior to shell calcification) and that the pointed end is caudal (furthest down the oviduct). These observations cannot be explained by peristalsis. Although it hasn’t been fully confirmed, it has been suggested[14] that the egg takes on its shape as it is pushed through the narrow isthmus, with the pointed part of the egg located at the caudal region. [citation needed].

Cliff-nesting birds often have highly conical eggs. They tend to roll around in a tight circle rather than rolling off, which is a trait that most likely developed as a result of natural selection. In contrast, many hole-nesting birds have nearly spherical eggs. [citation needed].

The shape has biological significance. A pointed egg with its big end tipped upward will usually rest on its side. Compared to the more pointed end, the big end has a higher density of pores piercing its shell, which houses the air sac. Tipping the large end upward enhances oxygen flow to the large head, which develops at the more pointed end and has the physiologically demanding eyes and brain. [citation needed].

A 2017 study published in the journal Science used mathematical modeling of data from 50,000 bird eggs to demonstrate that the shape of bird eggs is determined by flight adaptations rather than nesting circumstances or a bird’s life history. [16] On a wide range of taxonomic scales, a strong relationship was discovered between egg shape and the capacity for flight; consequently, birds that use strong winds to fly typically have elliptical eggs that maximize egg size while keeping a sleek body structure. [16] It is also believed that selection at work during incubation, such as breeding location and incubation posture, influences the variation in egg shape among birds. [17].

  • Classic oval bird egg (Spur-winged lapwing)
  • Almost spherical bird egg (Senegal parrot)
  • Long, “elliptical” bird egg (Common murre)

Shell edit

Bird eggshells are diverse. For example:

  • Cormorant eggs are rough and chalky
  • Tinamou eggs are shiny
  • Duck eggs are oily and waterproof
  • Cassowary eggs are heavily pitted

A bird’s eggshell has tiny pores that let the embryo breathe. The domestic hens egg has around 7500 pores. [9].


How do you tell if an egg is a bird egg?

In general, bird egg shells are made of calcium carbonate and so the default colour is white. But other pigments can create different colours and patterns. Birds that build their nests in trees and shrubs (like dunnock and blackbird) generally have blue or greenish eggs, either spotted or unspotted.

How small can a bird egg be?

Hummingbirds have the smallest eggs among U.S. species. Calliope hummingbird eggs are 12 millimeters long – less than half an inch. Generally speaking, Baicich says, “I think it is intuitive that the bigger the bird, the bigger the egg.” Birds can nest in unusual places.

Which bird egg is very big?

While an ostrich lays the world’s largest bird’s egg, it is actually the smallest in proportion to the mother at just 2% of her body weight. In fact, kiwi eggs are six times bigger than other birds of the same size.

What bird egg is the size of a pea?

The smallest bird egg belongs to the hummingbird and is the size of a pea.