Eggs' Records

Eggs are regarded as some of the most fragile things in nature. But when African ostrich eggs were tested, they supported a pressure of 120 kg!

Of course, they are the largest eggs: 4.3- 6.4 pounds (or 1.5-2 kg of which 280 g are represented by the shell) and equals some 36 chicken eggs. Crocodiles, even if they can reach up to a ton, depose small eggs compared to their mass, about the same size of the goose egg.

The eggs of the elephant bird (Aepyiornis) from Madagascar, the largest bird ever, hunted to extinction in the XVIIth century were even larger: up to 12,5 kg (27 pounds), 32 cm (13 inch) tall and 22 cm (9 inch) wide. A dinosaur egg found in Argentina was 1.6 m (5.3 ft) tall and 80 cm (2.6 ft) wide.

The smallest eggs in the world belong, as expected, to the smallest bird species, the hummingbird Mellisuga hellenae from Cuba: a 1.8 g adult lays a 0.2 g egg.

The kiwi bird possesses its egg record: a 2.5 kg (6 pounds) female lays a 450 g (1 pound) egg. This represents 20 % of her bodyweight and is the largest egg compared to the bird's bodyweight. (as a comparison, a chicken egg represents 4 % of the bird's bodyweight).

Instead, the cuckoo female lays one of the smallest eggs compared to its body size: just 2% of its bodyweight. This is an adaptation for nest parasitism: the eggs are laid in the nest of birds which are much smaller than the cuckoo (like warblers, flycatchers, thrushes) and a big egg would be highly conspicuous amongst the other eggs.

Scientists observed a link between the number of the eggs in a clutch and a bird's longevity. Big birds of prey (eagles, vultures) lay 1-2 eggs and usually breed once at two years.

Large penguins lay one egg, smaller ones 2 eggs.

In the birds without a fixed number of eggs in the clutch, extracting daily one egg from the nest makes them lay much more eggs. The little owl lays normally 406 eggs, but up to 13 eggs in 15 days in this case. The wryneck lays normally 7-10 eggs but up to 62 (!) in 62 days. The quail can produce 300 eggs annually. The largest natural bird clutch in nature is considered as being that of the gray partridge: up to 20 eggs.

The shape of the eggs is that that facilitates the maxim temperature during the incubation, depending on the number of the eggs and the place of the clutch. Albatrosses lay one egg perfectly round, easier to incubate. Doves make two oval eggs, which stay stuck one of the other, fact that possible if they would have been spherical. The guillemot (Uria alle) lays pear-shaped eggs, more secure on the edges of the cliffs, while the plover (Charadrius) lays 4 eggs, round at one top and sharp to the other, that collocate perfectly.

The incubation of eggs in case of birds can last from 10 days in white-eye and other small birds to 85 days in albatrosses and kiwi. Generally, larger birds incubate more.

In the so-called mound builders or incubator birds, males build mounds of soil mixed with dead leaves and sand. When it rains, the leaves start rotting and produce heat and the general temperature of the "incubator" is about 34o C.

The mound can be 1 m (3.3 ft) tall and 2-3 m (6.6-10 ft) wide. The females lay their eggs in the mound and the males take care to maintain the mound's constant temperature.

The offspring hatch after 50-100 days fully developed. Some birds can carry out their eggs if disturbed while incubating. This is the case of some owls, woodcocks and nightjars.

In the case of the white-headed duck, the eggs can auto-thermoregulate so that the young hatch even if the eggs were not covered in the last days of the incubation.

The lyrebird nests during the Australian winter, from May to October, in the snowed mountains. Only the females incubate the sole egg and the nest can be often covered by snow. This egg is extremely resistant to cold ...

In the places where food is abundant, some species tend to lay two clutches of 2-3 eggs, while in places poor in food, they lay just one clutch of 6-7 eggs. Nesting territory in the case of vultures can be of 7,000-9,300 hectares, while for the magpie it can be of 100-150 ha, and for some species 1,500 square meters.

Species nesting on the ground have mimetic colors (imitate the color of ground, sand, grasses), while those nesting in tree hollows (like hoopoes, parrots or woodpeckers) or in dens (bee-eaters) can be vividly colored. Of course, the nest of the nidifugous tend to be simpler than those of the nidicolous birds. Nidicolous birds incubate less than nidifugous birds.