Life Cycle of a Bird Part 6: Nothing Like Home Sweet Home Adult birds rarely makes nests for themselves but rather for raising their young. A nest is where the eggs are laid, incubated and where the young is raised. Nests come in all shapes and sizes, from a simple scrape in the ground to a complex structure or an 'ancestral pile'.
(Photo of Herons with nesting material by Rob O)
Not every bird species builds or uses a nest. Some auks lay their eggs directly onto the narrow rocky ledges they use as breeding sites. The egg's shape helps prevent the egg from rolling off. King and Emperor Penguins tuck their eggs between their feet and folds of skin on their lower bellies. They are thus able to move about while incubating the egg.
 The scrape nest is a simple depression made in the ground. It is sometimes lined with bits of vegetation, rocks, shells etc. This may help to incubate the eggs or prevent them from rolling away. Ostriches, most Tinamous, many Ducks, most Shorebirds, most Terns, some Falcons, Pheasants, Quails, Partridges, Bustards and Sandgrouse are among the species that build scrape nests.
(Photo of a Gentoo Penguin using a scrape nest by Valérie)
The Three-banded Courser and Egyptian Plover are unique in their habit of partially burying their eggs in the sand of their scrapes.
Other birds go the extreme of burying their eggs. Enormous mound nests are made of soil, branches, sticks, twigs and leaves. Once made, the bird will bury the egg in the middle. The heat generated by these mounds incubates the eggs. This method is used by the Megapodes. The Dusky Scrubfowl's mound measures more than 11m in diameter and stands nearly 5m tall.
A similar method is used by flamingoes and a few other birds. They make cone-shaped piles of mud between 15–46cm tall, with a small depression on the top to place their single egg.
(Photo of Australian Gannets (in a colony) using a 'cone-shaped' nest by Carmelo Aquilina) 
Birds sometimes dig burrows into the ground and use it as their nest. They may also use abandoned burrows which animals have dug. Bee-eaters are well known for their river bed burrow colonies. In this instance, a vertical wall is used for a horizontal tunnel. The longest nest burrow belongs to the Rhinoceros Auklet with a length of 8m.
The cavity nest, a method used commonly amongst Woodpeckers, Trogons, some Nuthatches and many Barbets. They make their own cavity in a dead or an alive tree. They are known as 'primary cavity nesters'.
(Photo of Blue-throated Barbet using a cavity nest by Mike Gillam)
However, some other birds use natural cavities or abandoned ones.  Parrots, Tits, Bluebirds, most Hornbills, some Kingfishers, some Owls, some Ducks and some Flycatchers are involved in this type of nesting. They are called 'secondary cavity nesters'.
(Photo of Galah Parrots inspecting a cavity by Julian Robinson)
One bird genus makes its nest entirely out of its own saliva: the Swiftlets. The saliva dries and hardens to form a bracket on the cave wall into which the birds lay their eggs. The nest is collected for a famous Chinese delicacy soup. Swallows, on the other hand, use mud for the structure which is then lined with grass and hair. It is fastened to vertical wall or underneath a ledge.
The smallest bird nests are those of the Cuban-Bee and Vervain Hummingbirds nests. The nest is cup-shaped and is 1,98cm wide and 1,98-3cm deep. Cup-shaped nests are generally made with grass but mud is also used. Many passerines and a few non-passerines, including some hummingbirds and some swifts, build this type of nest. Smaller birds use considerable amounts of spider silk in the construction of their nests. It is both strong and extremely flexible, allowing the nest to mold to the adult during incubation (reducing heat loss), then to stretch to accommodate the growing nestlings.
 The platform nest is a large structure, often much bigger than the birds which build and use it. In the case of raptors, these nests are often used for many years thus being called the 'ancestral pile'. New material is added each breeding season. The nest may grow so large that it will even cause structural damage to the tree. The Bald Eagle has made a nest which is 6,1m deep, 2,9m wide and weighing 2 722kg.
(Photo of a Bald Eagle in the Public Domain by US Fish and Wildlife Digital Asset Library)
Oropendolas, Caciques, Orioles, Weavers and Sunbirds are among the species that weave pendant nests. Pendant nests are elongated sacs woven of pliable materials such as grasses and plant fibers and suspended from a branch. The African Socialable Weaver has a pendant nest which consists of 100-chambers. It is 8,2m in length and 1,8m high, making it the largest social nest.
Video of a Sociable Weaver colony by David Attenborough on Youtube, worth a watch.
This chapter concludes my Life Cycle of a Bird series as the next step is egg laying.
I hope you've enjoyed it
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1Comment
at Thursday, 18 December 2008 14:28
I've seen nests of the Dusky Scrubfow in Daintree Rainforest, in Oz. They are huge!
Thanks for another interesting post, Candy. Love the YouTube clip too. The whole series has been an excellent read!
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