I have just read an article on superprecociality in pterosaurs whereby baby pterosaurs could fly immediately after hatching and even occupy different niches from their parents. It occurred to me that there is one group of modern birds that could do just that! They do not incubate their eggs with their body heat like other birds, but bury their eggs under massive nest mounds of decaying vegetation. Neither do they brood their young with body heat after hatching (other precocial chicks are not independent in thermoregulation and are unable to regulate their own body temperatures and so require parental brooding). In fact they are left on their own to hatch, dig themselves out of the nest (in the manner of newly hatched turtles) and immediately fend for themselves. I thought I should introduce this remarkable group of birds as well as the concept of precociality to this forum. These birds are the Megapodes.
Megapodes are an interesting Australasian family of birds closely related to the Gamebirds (Galliformes). They are also known as incubator birds or mound-builders, and are stocky, medium to large, chicken-like birds with small heads and large feet in the family Megapodiidae. Bird hatchlings, like new-born mammals, can be precocial where the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called altricial, where the young are born or hatched helpless as in songbirds. Examples of precocial birds include the domestic chicken, many species of ducks and geese, waders and rails. Extremely precocial species are called "superprecocial". Megapodes are "superprecocial", hatching from their eggs in the most mature condition of any bird. They hatch with open eyes, bodily coordination and strength, full wing feathers, and downy body feathers, and are able to run, pursue prey, and in some species, fly on the same day they hatch. Megapodes do not incubate their eggs with their body heat as other birds do, but bury them. Their eggs are unusual in having a large yolk, making up 50 - 70% of the egg weight. The birds are best known for building massive nest mounds of decaying vegetation, which the male attends, adding or removing litter to regulate the internal heat while the eggs develop. However, some bury their eggs in other ways: there are burrow-nesters which use geothermal heat, and others which simply rely on the heat of the sun warming sand.
Nest Mounds and Nesting sites:
1. Top to bottom:
a. Malleefowl Nest Mound (Malleefowl nest mounds can be over 1m in height and 4m across. The male buries wet leaf litter in the mound, which gives off heat as it rots, acting as a natural incubator for the eggs. Throughout the breeding season, the male has to ensure that the temperature inside the mound is maintained at about 33°C. Temperature is maintained by digging the nest and by adding or removing sand).
b. Australian Brushturkey Nest Mound (They build large nests on the ground made of leaves, other compostable material, and earth, 1 to 1.5 metres high and up to 4 metres across. The eggs are hatched by the heat of the composting mound, the temperature of which is regulated by adding or removing material to maintain the temperature in the 33 to 35 °C incubation temperature range.The same nesting site is frequently used year after year).
c. Mound of the Orange-footed scrubfowl (Megapodius are best known for building a massive mound of decaying vegetation, which the male attends, adding or removing litter to regulate the internal heat while the eggs hatch)
2. Top to bottom:
a. Moluccan Scrubfowl burrows at nesting site (The nesting grounds are usually located in sun-exposed beach or volcanic soils.The Moluccan megapode is the only megapode known to lay its eggs nocturnally).
2. Close-up of Maleo nest.
3. Maleo Nesting Site (The Maleo is a mound builder that uses volcanic and solar-heated sand to incubate its eggs in large colonial nesting grounds).
3.Top to bottom:
a. Illustration of Malleefowl covering its Eggs with sand.
b. Pair of Malleefowls atop Nesting Mound.
Instead of a sharp dividing line between hatchlings that are precocial and those that are altricial, there is a gradient of precociality.
Precocial: There are four levels of precociality. Level 1 of development (precocial 1) is the pattern found in the chicks of megapodes (Australian Malee fowl, Brush Turkeys, etc.), which are totally independent of their parents ("superprecocial"). The megapode young are incubated in huge piles of decaying vegetation, and upon hatching dig their way out, already well feathered and able to fly. Precocial 2 development is found in ducklings and the chicks of shorebirds, which follow their parents but find their own food. The young of game birds, however, trail after their parents and are shown food; they are classified as precocial 3. Precocial 4 development is represented by the young of birds such as rails and grebes, which follow their parents and are not just shown food but are actually fed by them.
Semi-precocial: Hatched with eyes open, covered with down, and capable of leaving the nest soon after hatching (they can walk and often swim), but stay at the nest and are fed by parents. Basically precocial but nidicolus (young that remain in the nest), this developmental pattern is found in the young of gulls and terns.
Semi-altricial: Covered with down, incapable of departing from the nest, and fed by the parents. In species classified as semi-altricial 1, such as hawks and herons, chicks hatch with their eyes open. Owls, in the category semi-altricial 2, hatch with the eyes closed. If all young were divided into only two categories, altricial and precocial, these all would be considered altricial
Altricial: Hatched with eyes closed, with little or no down, incapable of departing from the nest, and fed by the parents. All passerines are altricial.
Megapodes are divided into 3 Groups:
1. Scrubfowl Group - 3 living genera
1a. Genus:
Macrocephalon - 1 species, Maleo (
Macrocephalon maleo).
Top to bottom:
a. Maleo (
Macrocephalon maleo).
b. Hatchling. Note the fully formed flight feathers.
c. Comparative sizes of egg and newly hatched chick.
1b. Genus:
Eulipoa - 1 species, Moluccan megapode (Eulipoa wallacei).
Top to bottom:
a. Moluccan scrubfowl (
Eulipoa wallacei)
b. Moluccan scrubfowl in burrow laying eggs
1c. Genus:
Megapodius - 13 species.
Here are 3 examples:
Top to botttom:
a. Micronesian scrubfowl (
Megapodius laperouse).
b. Nicobar scrubfowl (
Megapodius nicobariensis).
c. Philippine scrubfowl (
Megapodius cumingii).
Another 2 examples:
Top to botttom:
a. Tongan scrubfowl (
Megapodius pritchardii).
b. Orange-footed scrubfowl (
Megapodius reinwardt).
c. Orange-footed scrubfowl, juvenile with adult wing feathers.
2. Malleefowl Group - 1 genus
2a. Genus: Leipoa - 1 species, Malleefowl (
Leipoa ocellata)
Top to bottom:
a. Malleefowl (
Leipoa ocellata).
b. Hatchling. Again, note the fully developed wing feathers.
c. Hatchling in hand.
3. Brushturkey Group - 3 living genera
3a. Genus:
Alectura - 1 species, Australian brushturkey (
Alectura lathami)
Top to botttom:
a. Australian brushturkey (
Alectura lathami).
b. Hatchling. Note the fully developed wing feathers.
c. Hatchling, showing wing feathers.
3b. Genus:
Aepypodius - 2 species
Top to botttom:
a. Waigeo brushturkey (
Aepypodius bruijnii).
b. Wattled brushturkey (
Aepypodius arfakianus).
c. Wattled brushturkey Hatchling.
3c. Genus:
Talegalla - 3 species
Top to bottom:
a. Black-billed brushturkey (
Talegalla fuscirostris).
b. Red-billed brushturkey (
Talegalla cuvieri).
c. Collared brushturkey (
Talegalla jobiensis).
4. Extinct Giant Malleefowl
Top to bottom:
a. Progura gallinacea, the extinct Giant Mallee fowl.
b. Comparisons of skeletal elements of
Progura gallinacea and
Leipoa ocellata to indicate relative size
.
Megapodes are the only extant birds with "superprecocial" chicks, which leave the nest immediately after hatching and do not receive any post-hatching parental care. Kiwi hatchlings likewise spend only a very short time in the nest and though not really "superprecocial" (they are advaced level 2 precocial), are more precocial than the young of most other extant birds. Kiwi chicks hatch as mini-adults - fully feathered and open-eyed. Kiwi parents do not need to feed their young because the chick can survive off the rich egg yolk for several days. At the end of this time, a kiwi chick may weigh only 80% of its hatching weight. After two or three days, enough of the yolk sac has been absorbed to allow the baby kiwi to stand and shuffle around the nest. This yolk sustains the chicks for their first 10 days of life – after that they are ready to forage for their own food.
Top to bottom:
1 day old Kiwi chick. Note the large yolk-filled abdomen. No wonder the Kiwi lays the largest eggs for its size of any bird!
5 day old Kiwi chick, Yolk almost all resorbed.
The extinct Enantiornithes are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. The name "Enantiornithes" means "opposite birds", i.e. the opposite of modern birds. Known enantiornithine fossils include eggs, embryos, and hatchlings. An enantiornithine embryo, still curled in its egg, has been reported. These finds demonstrate that enantiornithine hatchlings had the skeletal ossification, well-developed wing feathers, and large brain which correlate with precocial or superprecocial patterns of development in birds of today. In other words, Enantiornithes probably hatched from the egg already well developed and ready to run, forage, and possibly even fly at just a few days old. So the extinct Enantiornithes (and pterosaurs) were also "superprecocial".
3 reconstrucuions of Enantiornithes:
Top to bottom:
a.
Cratoavis.
b.
Parvavis.
c.
Shanweiniao cooperorum.
Lastly, not all large flightless birds are Ratites. Sylviornis is an extinct genus of stem-galliform bird containing a single species, Sylviornis neocaledoniae, or erroneously, "New Caledonian giant megapode" (Technically, this is incorrect because it has recently been found not to be a megapode). It was a huge flightless bird, 1.7 m (5.6 ft) long altogether, and weighing around 30 kg (66 lb) on average. It is the most massive galliform known to have ever existed. Even larger were the Dromornithidae, known as Mihirungs and informally as thunder birds or demon ducks. They were a clade of large, flightless Australian birds of the Oligocene through Pleistocene Epochs, long classified in Struthioniformes, but are now usually classified as galloanseres (with water fowls and game birds). One species, Dromornis stirtoni, was 3 m (9 ft 10 in) tall.
Restorations:
Top to bottom:
a.
Sylviornis neocaledoniae.
b.
Dromornis stirtoni.
[Information from Wikipedia and other sources]