BUDGERIGAR BREEDERS often comment on fertile eggs, which fail to hatch because the chicks die during incubation. There are a number of reasons for these failures, which will be discussed below.
In the first few days chick death is usually due to inadequate incubation. This can be from half hearted or intermittent sitting by the hen and subsequent low incubation temperatures or excessive jarring of the egg that fatally damages either the chick, or the yolk; this is sometimes caused by the breeder when hand-checking the eggs but seldom by the birds themselves. Finally, the other possible causes are a genetic fault and a bacteriological infection. Eggs that die at this time are addled.
Towards the end of incubation, chicks usually die as a result of hatching problems. As the 18th day of incubation approaches, and the hatching process commences, there are a number of things that can happen which will prevent successful hatching. Chicks that die at this time are dead in shell.
For the period between the beginning and the end of incubation, the chick is growing and developing and it is this time when nutritional needs and exposure to infection become significant, as any problem with either, will result in death for the chick.
Embryonic Death at the Start of Incubation:
With deaths early in incubation, the egg is, in fact, fertile but the embryo is poorly developed. The usual cause is poor incubation causing the egg to become cold after development has started. Possible causes include improper nesting material, excessive interference by the aviculturist, inadequate control of nest mites, overcrowding in the aviary, old arthritic birds, poor nest-box design, competition with other birds within the aviary, poor parenting, nest box which is too hot, too cold or poorly ventilated and external disturbances.
Eggs are also very vulnerable to vibration type injuries early in incubation. Shaking or jarring the egg can kill the developing embryo either directly or by rupturing the yolk. This is of particular relevance when eggs are being transferred for fostering. Embryos that are unlucky enough to have genetic abnormalities also usually die early in incubation. Genetic problems are more likely to occur with inbreeding.
Deaths from Days 4 to 14 of Incubation:
This is the longest period of the incubation process and yet it is the time when least deaths occur. The embryo is simply growing. The growing chick receives its nutrition from the yolk and deaths here can reflect nutritional problems in the hen. Hens that are fed correctly are more likely to produce nutritious yolks that support healthy embryos. The effect of breeding bird nutrition is very underrated. By only feeding a blend of 2 or 3 seeds and a calcium supplement, such as grit, it is not possible to prepare the hens for breeding.
Although embryos can die of infection at any time during incubation, it is at this time of growth that they are most vulnerable. Certainly, some infections, eg. Chlamydophilosis and Salmonella can be carried by the hen and infect the ovary. These can be incorporated into the egg at the time of its formation and subsequently infect and kill the embryo as it grows. Infection can also pass through the oviduct wall into the egg. However, these types of infections that enter the egg prior to laying are in the minority. Most infections that develop are contracted in the nest, after hatching. Nests that are dirty, poorly ventilated or excessively humid can cause eggshell contamination and movement of infectious agents into the egg.
Egg quality is also important. Cracked, thin, misshapen or rough eggs allow easier entry of infection and are more prone to trauma. Poor eggs can be caused by oviduct disease, but are more often associated with nutritional deficiency, in particular, calcium. Some aviculturists may have noticed eggs with translucent clear lines running around the outside of the egg.
Embryonic Deaths at the End of Incubation:
Through incubation, a membrane called the chlorioallantois develops around the chick. The chlorioallantois is similar to the human placenta, in that it delivers air to the embryo after it diffuses through the shell. At the end of incubation the chick must swap from chlorioallantoic respiration to breathing air. It does this i two stages: First, it pips internally. The chick cuts a small hole into the air chamber at the end of the egg and starts to breather the air that it contains. At this stage vibrations can be felt in the egg and the chick will sometimes vocalise.
After another 12 to 36 hours the second stage begins, with the chick cracking the shell and breathing external air. While this is happening the last of the yolk sac, which is the chick’s nutrition during incubation, is drawn into the navel. This eventually ends up as a tiny sac in the wall of the small intestine, called Merkels diverticulum which remains there for the whole of the life of the bird. Interestingly, during this time, the chick also drinks the clear fluid around it. This fluid, called the amniotic fluid, along with the yolk sac, contain the antibodies that protect the chick from infection in the first few weeks of life.
While all this complex physiology is occurring, the chick is vulnerable to problems. If the temperature or humidity is too high or too low during this time the chick will be adversely affected. The usual problem is that the temperature is too high, or the humidity is too low. The combination causes the shell and the shell membrane to become dry and hard. This can lead to a healthy chick becoming exhausted. In addition to this, the chick quickly becomes dehydrated. I am sure that many of yu, myself included, have helped these chicks hatch, only to find them dead later. These chicks often die because they are dehydrated. Such chicks, if given small drops of water, will often suck them down greedily and survive. These dehydrated chicks are called “sticky chicks” because of the way they stick to the dry shell membranes. They are often found dead after hatching, a quarter to half-way emerged from the shell. If removed fro the shell, they often have unabsorbed yolk sacs and the egg often contains dry, gluggy albumen.
To assist in keeping nest box humidity at the correct level, either provide a bath for the birds, or, if that is not possible, the eggs and the underside of the hen can be lightly misted with water from a spray bottle. The nest box should, ideally, have a humidity level of 70% and the sitting bird needs to keep the eggs at between 36.5C – 37.0C.
hatchability can be dramatically improved by the following three simple steps:
Improve nutrition in the months prior to breeding
Provide a clean nest for every clutch, and on-going nest box hygiene
Provide access to rai or a bath around hatching time.
If attending to these matters does not help, your avian veterinarian will usually want to review the aviary environment and your management, practices, test the hen for infection or do an egg autopsy!!