3 things you should know about bird breeding — Part 1 Temperature
What are the most important parts when it comes to artificial incubation of bird eggs?
About artificial incubation in general
Artificial incubation is defined as the incubation of eggs in an incubator, as opposed to natural incubation provided by the parents or the surrounding temperature. Natural incubation and artificial incubation can be combined, too, e.g. by letting the parents incubate the eggs first for a certain length of time before putting the eggs in an incubator until they hatch. This short article covers the incubation of bird eggs in electric incubators.
The hatch rate of fertile eggs from captive breeding depends on many factors. Some are environmental factors like the intensity of sunlight inside the breeding pens or the climate of the country where the breeding pens are situated. Other factors are man-made like the food for the breeding couples before and during the breeding season. While some factors influence the hatch rate even before the egg was laid, other factors apply only after the incubation by the parent birds has started. The second group of factors can be eliminated by artificial incubation.
The three main parameters of artificial incubation are the temperature inside the incubator, the turning of the eggs, and the weight loss of the eggs during the incubation period. This short treatise will deal with these three main factors of the artificial incubation.
1. The temperature
With most modern incubators the heating is done by a heating wire or a heating element which is regulated by an electronic thermostat. There are two fundamental types of incubators as far as the distribution of the heat inside the incubator. The still air incubators have the heating wire on top of the inside of the incubator and the heat distribution is left to the physics, i.e. the warm (and less heavy) air is on top and the cooler air is on bottom. In between there are the layers with intermediate temperatures. As the air does not move around inside this type of incubator, it is crucial where the sensing device of the electronic thermostat is placed. The same applies to the control thermometers. They either have to be placed exactly at the middle of the eggs concerning the height or, if they are placed higher because of the turning mechanism, it has to be considered that the temperature above the eggs is already higher than at the level of the eggs. As most still air incubators open on top by lifting and taking off the lid they are very sensitive to opening the incubator. Every time the top is opened all warm air is gone and after closing the lid again it takes quite some time till the temperature layers are stable again and at the right temperature. Therefore, the still air principle is used nowadays only for very cheap polystyrene incubators for users who breed eggs only from time to time. They are better used for waterfowl or gamebirds who in nature leave their nest in search of food for longer periods than for birds that are fed by their partner and therefore, seldom leave the eggs uncovered.
With bird species that rarely leave their eggs uncovered, forced air incubators are used. Big commercial poultry producing companies use only forced air incubators, too, but their devices are far larger than an average incubator.
The advantage of forced air incubators is that one or more ventilators transport the warm air from the heating elements to every spot inside the incubator. Therefore, theoretically the temperature should be equal for every egg inside the incubator. Theoretically, because all incubators have a rectangular inner space and the air does not circulate in the corners in the same manner as in the middle of the compartment or near the ventilators. The air circulation depends on other factors like the form of the turning mechanism, the number of the eggs in the incubator and the number of the layers of egg trays. The most uniform heat distribution inside the incubator can be achieved when there is only one egg tray and only a small number of eggs is placed in the middle of that egg tray. When the eggs that should be incubated are of high value, it is a good idea to check each place on the egg try with an exact and calibrated thermometer and make a heat distribution map of that incubator. Spots that show divergent temperature should be avoided, and it is a good idea to either replace removed eggs with dummy eggs or move the remaining eggs closer together.
The single most important items monitoring the temperature during the incubation process are precise control thermometers. Whereas today the thermostats are all electronic, for the surveillance of the temperature both electronic/digital and analogue thermometers are used. Precise and calibrated bulb thermometers are still the backbone of a successful breeding facility. Most precise bulb thermometers of the past were mercury thermometers. Since October 2017, selling and shipping of thermometers containing mercury is forbidden within the European Community. Therefore, we will be forced to rely upon more and more digital thermometers in the future. But it is alarming how many thermometers don’t show the exact absolute temperature. Some thermometers, no matter if digital or bulb, show as much as 0.25°C deviation from the real temperature.
This explains cases in which some breeders incubate their eggs at strange temperatures and still have success. If someone uses a thermometer that shows 0.2°C less than the actual temperature, i.e. 37.5°C instead of 37.7°C, and has the best hatch rate at 37.3°C then he incubates in reality at 37.5°C (that’s the normal incubation temperature for most bird eggs).If the thermometer located farther away from the eggs (in most cases above or below) then the deviation will be reinforced or lessened. When a less experienced breeder follows the example of the successful breeder and wants to breed himself the eggs at 37.3°C then three things might happen if he don´t have a calibrated thermometer. In the best case his thermometer shows 0.2°C less than the real temperature. Then he incubates his eggs actually at 37.5°C and his hatch rate will be normal. If his thermometer shows the precise temperature than he will breed at 37.3°C and will have fewer hatched chicks than normal. In the worst case, his thermometer shows 0.2°C too much. In this case he will actually breed at 37.1°C, and his hatch rate will be a disaster. It´s always a good idea to question the statements of other breeders. Can they be substantiated or did that breeder makes a mistake himself without knowing it? I witnessed more than once in the past that the hatch rate dropped when a deviating thermometer of a successful breeder broke and was replaced by a precise one or even one that deviates in the other direction. Therefore, it is a very good advice to calibrate the thermometers before every breeding season and to make a map of the temperature zones of every new incubator that is bought.
Experience and experiments have shown that the hatch rate in incubators is best when the eggs are incubated at 37.5°C. Now let´s have a look at that temperature. In fact this temperature is an arithmetical mean temperature. The body temperature of awake birds differs between 40–42°C. During the sleep the birds can bring down their temperature. If this is the case with incubating birds, too, we don´t know. Many birds even lose their feathers on the stomach so that there is a better heat transfer from the skin of the adult bird to the upper side of the eggs. So why do we incubate at 37.5°C when the body temperature of the breeding bird is much higher? To answer this we have to go from the upper side of the bird egg that is heated by the mother skin with 40–42°C to the lower side of the egg. Below the egg is the nesting material or the soil. In the case of nest building birds there will be twigs or branches lined with feathers, down, grass, hairs of other animals etc. In the case of some ground nesting birds there will just be a scrape on the ground and the material below the eggs will be cold soil or gravel. Of course the ground will warm up a bit during the incubation but will never reach the temperatures on top of the egg. So it´s warm on top, cold on the lower surface and in between in the middle of the egg. And the above mentioned 37.5°C seem to be the average temperature where the hatch rate is highest.
At the beginning of the incubation period the embryo in the egg always floats on the top side of the egg. Therefore with natural incubation the embryo gets a higher temperature during the early stages of his development at the same average of 37.5°C compared to the artificial incubation in forced air incubators where the temperature is equal throughout the entire inner space of the incubator. Later on, when the embryo is less mobile within the egg the advantage of natural incubation is less pronounced. To profit from the superiority of natural incubation during the early stages, one can leave the eggs with the parents or other birds for 7–10 days. After this period of natural incubation the eggs are placed in the incubator until they hatch.
Stay tuned for the next part about turning the eggs in the incubator.
In the meantime you can download our App for free at the Play Store: https://play.google.com/store/apps/details?id=net.hatchapp
