• Correct incubation conditions are important for development and hatching of eggs. The required conditions vary considerably between species, and some species appear more exacting in their requirements than others. Minor deviations in correct temperature may lead to a slightly shortened or lengthened incubation period, while greater variation may cause failure to develop or hatch, or result in weak chicks. Incorrect incubation conditions have also been implicated in some developmental problems of neonatal birds.
• In general, correct incubation conditions are most crucial early in incubation, with small variations being tolerated better by the embryo later in development. For this reason, eggs are sometimes left with the parents initially for seven to ten days until they have been "set" and transferred to an artificial incubator after this most crucial period, in the hope that the birds will then lay again. Alternatively, eggs are placed under a broody initially, before being placed in an artificial incubator. Both procedures may improve hatching success compared to complete artificial incubation.
• Egg cleanliness is of vital importance; it has been shown that poor hygiene and dirty eggs may significantly reduce the percentage of eggs hatching successfully. It is important that the laying sites are clean as well as conditions following egg collection. Eggs cool down once laid, therefore the contents shrink and air is drawn into the egg: bacteria may be drawn in at the same time. Invasion of bacteria such as Staphylococcus spp., Salmonella spp. and Escherichia coli may lead to death of embryos or neonates. Eggs may be cleaner if they are collected immediately after laying rather than after they have been "set".
• Eggs which are deformed should not be incubated.
• Eggs which are noted to be cracked at the time of collection are generally discarded, and grossly contaminated eggs may also be discarded at this time. If such eggs are particularly valuable, they should be separated from other eggs for incubation, due to the greater risk of infection.
• Eggs which become cracked during incubation may be repaired, if the crack is small, with e.g. surgical grade cyanoacrylate glue, candle wax dripped onto the crack, nail varnish, correction fluid or sticky tape (it has been suggested that products containing acetone should be avoided, due to possible toxicity B12.5.w10). Eggs which are cracked should be incubated in an incubator (not under parent or broody), with extra care taken in their handling and monitoring. It is important to ensure that the material used to cover the crack is applied to the minimum surface of the shell required to seal the crack. A thin layer of bone cement may be applied over a crushed area of shell and a hole in the shell may be repaired by gluing an appropriate piece if sterilized shell, parafilm, tissue or gauze over the defect. Care should be taken to avoid sealing over larger areas of the shell than absolutely necessary as this prevents necessary gaseous exchange.
• If the shell membranes have been penetrated the egg is likely to have become contaminated with pathogens and the yolk, embryo or blood vessels may have been physically damaged. Hatchability is greatly reduced.
• A pipped egg which is being parent or broody incubated and becomes damaged should be moved to a hatching incubator.
• Eggs which fail to hatch normally may require assistance.

(J3.103.w1, B12.5.w10, B29, B37.x.w1, B41, B108, B115.4.w1, B119.w1, B139, P3.1987.w1).

• Records: Accurate and detailed records are very important in incubation. All eggs should be individually identified and details recorded including the identity of the parents, and details of their pedigree, nutrition and breeding and incubation behaviour, initial weight, date of setting, details of incubation such as results of candling, incubator used, weight loss (if this is being monitored) expected and actual hatching dates, as well as evaluation of the hatched chick or results of investigation into eggs which fail to hatch.

(B42, B119.w1).

• Candling
• Formaldehyde Fumigation of Incubators
• Necropsy - Egg Necropsy
• Waterfowl Egg Collection & Storage
• Management of Hatching Bird Eggs

• Parent incubation generally provides the ideal conditions of temperature and humidity for development and hatching. However, not all species or individuals are equally good sitters, particularly in captive situations, in which birds may be disturbed and not feel secure. Additionally, small species in particular are vulnerable to predation while sitting, especially if nesting in an open site. Also, normal incubation behaviour may not be suitable for birds being maintained in an environment very different from their native habitat.
• If allowed to sit, hatch and rear their chicks, most birds will produce only one clutch a year, whereas two, three or even more clutches of eggs may be produced if the eggs are removed.
• It may be less easy to monitor parent-sat eggs for fertility and continued development, with an attendant risk of disturbing the birds.
• In captive conditions it may be more likely that nesting materials will not be fresh and clean, but contaminated with droppings, or include mouldy vegetation.

(B42, B106, V.w5)

• As with other birds, parent incubation should provide the optimum conditions for the developing embryos.
• In mixed-species enclosures there may be competition for nest sites and also dumping of eggs by some birds into the nests of other birds. In general, a pair of waterfowl occupying their own pen are less likely to be disturbed by other birds and more likely to sit successfully.
• Both predation (of eggs and of the sitting female) and disturbance may be major problems, particularly for birds that have chosen sites which cannot be described as ideal.
• Swans and geese frequently are good at sitting their own eggs, and ducks may also sit tightly if not disturbed excessively. Swans and many geese are commonly left to sit their own eggs, and to rear the young. Their larger size, well-defined territories and continuing strong pair bond reduces the chance of losses from predation of eggs.
• With species such as the Cape Barren goose (Cereopsis novaehollandiae - Cape Barren goose), which lay their eggs during the winter, consideration must be given to the practicalities of incubation in winter conditions and the additional stress placed on the birds, unless they are in sheltered winter accommodation.
• Most species of waterfowl can be stimulated to lay a second clutch of eggs if the first clutch is removed. However, females commonly change their nesting site due to the "predation" of the eggs and may stop laying if eggs are removed from all nesting sites. It may be advantageous to allow birds to sit and hatch eggs of their own or another more common species after a second clutch has been laid.
• Birds which are sitting may leave the nest for only a short time each day. In species in which only one parent incubates the bird may lose a considerable amount of weight over the period of incubation and it is important to ensure that food is freely available at whatever time the bird leaves the nest to feed.
• Waterfowl species vary in their response to disturbance at the nest site. Some are quite tolerant but others will desert the nest if subject to any disturbance. This makes regular inspection of the eggs for fertility and development difficult.
• N.B. in allowing waterfowl to sit, hatch and rear their own offspring consideration should be made as to the likelihood of predation of the downies, whether or not suitable food will be available or can be provided, and the ease or otherwise of catching the downies to pinion them, if this is required. Leaving non-native species full-winged in open enclosures may be detrimental to local species and may also be illegal.

(B30, B40, B41, B94, B97, B128, P3.1987.w1, V.w5)

• --

• Broody hens are commonly used in aviculture and have been described, if properly managed, as "still the finest incubator yet developed" (B106). They have the advantage of being relatively simple to manage. In order to be sure that broodies will be available when required, a flock of appropriate hens must be kept, with attendant costs. The possibility of the hens carrying and transmitting disease must always be considered.
• Silkies crossed with game hens are often considered to make ideal broodies.
• Ideally, a broody should be given a clutch of eggs all of the same species and stage of incubation to sit.
• Broodies may not be suitable for very small or very large eggs. Eggs with abnormally thin or abnormally thick shell, in which maintaining correct weight loss is difficult and requires considerable manipulation of humidity, are not suitable for broody incubation.
• Eggs which have been cracked or otherwise damaged should not be left under a broody for incubation.
• Additional manual turning may be required with very large eggs.
• Some broodies may not turn a coloured eggs mixed with white eggs.

(B37.x.w1, B106, B139)

• Broody hens may be used for incubating most waterfowl eggs. Obviously, carefully-selected reliable broodies should be used. Silkie-cross bantams are often considered excellent broodies, although larger hens may be required for larger eggs such as goose eggs (and small broodies should be used for small eggs). Good broodies are less easy to find now than previously, and a flock should be kept so that birds will be available at the correct time. A good steady broody is "worth her weight in gold".
• Each broody should be provided with her own broody box. The box should be just large enough to contain the broody on her nest, and should be dark when the door is closed. This may be placed directly on the ground outside (with wire netting underneath to keep vermin such as mice and rats out), or under cover in a shed or barn. If outside, the boxes should be placed under a tree on in a similar shaded position. The bottom of the box should contain a thick turf turned grass-side down and with a hollow prepared in the middle for the eggs, and soft bedding over this. The turf should be thoroughly dampened prior to the start of incubation, and assists in conserving moisture. It is essential that sufficient bedding is available or the hen may scrape right down to the bottom of the box, with an associated risk of eggs becoming broken. Humidity may be increased during the incubation period by spraying eggs with water (e.g. with a plant mister) and damping turf while the broody is off the eggs. The amount of water required will vary depending on the weather and the siting of the nest boxes, with boxes directly on the ground requiring less dampening, except in very dry conditions.
• Additional hand turning of eggs may be advantageous, particularly with very large eggs which may be less likely to be turned sufficiently by the broody.
• The broody should be dusted with louse powder prior to incubation and put down on several dummy eggs initially to confirm that she is sitting tight. Hens are best introduced at dusk, as they appear to settle best at this time. Once daily the front of the brooder box should be opened and the hen allowed off the eggs, or lifted off gently if necessary (with care that eggs are not lifted up under the wings), for a short time to eat, drink, defecate and dustbathe. Good broodies will usually return to their eggs after a short time, or they may be encouraged to return. They should be off no more than five to ten minutes initially, although up to half an hour may be acceptable late in incubation if the weather is warm. Care must be taken if a broody must be placed back on her eggs that she does not damage eggs, for example by "pedaling" with her feet
• Each broody box may lead out into its own small run, or several boxes may be placed in a yard or barn. Broodies will usually go back to their own box; it has sometimes been suggested that each should be tied by the leg to their box, although birds may be irritated by this and not sit properly.
• Records should be kept indicating for each broody box indicating which hen is sitting, when she began sitting, when the present set of eggs was introduced and when they are due to hatch or to be moved, for example into an incubator.
• The amount of moisture required may vary depending on the eggs. Eggs which would normally be laid and sat on in a damp marshy situation may require a higher humidity than eggs which are normally sat on in a dry tree hole.
• Best results are obtained if the eggs under any one broody are all of the same species and stage of incubation: a whole clutch should be set under the broody together.. Results may be much poorer if a mixture of eggs of varying ages and mixed parentage are placed under the broody.
• Ducks, for example mallard (Anas platyrhynchos - Mallard), may also be used to sit difficult eggs, e.g. Hooded merganser - (Lophodytes cucullatus - Hooded merganser). Mallard ducks, once sitting, make very reliable broodies. Domestic waterfowl may also be used, particularly Call ducks, and ringed teal (Callonetta leucophrys - Ringed teal) may be used for example to sit eggs from Smew (Mergellus albellus - Smew) or Bufflehead (Bucephala albeola - Bufflehead), which lay very similar eggs (B29, B41).

(B7, B29, B40, B41, B95, B97, B106, B108, B139).

• Artificial incubation is commonly used in aviculture. Eggs incubated in this way are safe from predation and are not at risk of being deserted by the bird sitting on them, for example due to disturbance. Eggs in incubators are at risk if the power supply to the incubator fails, for example if there is an electrical power cut.
• Artificial incubation allows many more eggs to be incubated than parent incubation and with less effort than maintaining broodies. However, very precise control and attention to the progress of individual eggs is required for the best results.
• Accurate control of temperature and humidity are vitally important in artificial incubation. Cleanliness is also very important; the ease with which an incubator may be cleaned and disinfected is an important consideration when choosing an incubator.

Incubation Facilities:

• The area in which incubators are kept should be easily cleaned and well ventilated, and should also be maintained at a constant temperature.
• Most modern incubators are electric, although paraffin and gas powered incubators do still exist. Incubators vary greatly in size, may be still air (in which air moves by convection) or forced air (in which air is moved using a fan) and may or may not include automatic egg turning.
• All incubators also require added water to maintain the correct humidity. This is usually provided in the form of one or more water trays.
• Still air incubators, which have a temperature gradient from the top (higher temperature) to the bottom of the incubator may approximate the natural conditions in a nest (in which the incubating parent is providing heat from above), but they may easily be overloaded and the eggs then poorly ventilated. Forced air incubators have a much more uniform temperature throughout, and better ventilation, and may be used for many more eggs.
• N.B. Individual preference plays a large part in choosing an incubator. In general, better results are likely to be obtained if the operator is familiar with, and comfortable using, the incubator.
• Incubators should be cleaned and disinfected (and fumigated if required - see: Formaldehyde Fumigation of Incubators) before the breeding season. A disinfectant suitable for incubators should be chosen and care is needed in cleaning the Once clean, they should be set up without any eggs and switched on.
• After the incubator has warmed up and appears to be at the correct operating temperature, it may be tested by incubating some bantam eggs. The temperature should be monitored and recorded several times daily, but adjusted on the basis of average daily readings rather than by micro-correction every few hours.
• Wet-bulb readings should also be monitored to indicate humidity levels. A pattern of a slight rise in readings on the wet-bulb thermometer may indicate a soiled wick and this should be changed (B42).
• For ideal results, all the eggs inside one incubator should be of the same age (stage of incubation) and size. In practice, eggs of different sizes and ages are commonly incubated in the same machine.
• Eggs close to the end of incubation produce a considerable amount of heat and therefore contribute locally to the air temperature, particularly in a still-air incubator.
• Large late-incubation eggs should not be placed near to small, newly-set eggs as they may affect their incubation temperature.

Temperature:

• Incubators are most reliable if kept in a room with a constant temperature. Maintaining a steady incubator temperature inside a room which varies widely in temperature is practically impossible.
• The temperature inside an incubator should be measured with a thermometer. This may be either a traditional mercury thermometer or an electronic thermometer. The bulb of the thermometer may be placed inside a blob of Plasticine or similar to reduce changes in readings due to minor fluctuations and give an average reading. It is important to make sure that the readings on the thermometer are accurate or, if there is an error, that the error is known, stable and can be corrected for. New thermometers should be checked against one known to be accurate. Either traditional mercury thermometers or digital thermometers may be used.
• Even in a forced air incubator there will be differences in temperature within an incubator, which may be mapped by placing thermometers in different places within the incubator. In a still air incubator the temperature varies vertically within the incubator and there may be a difference of several degrees between the bottom and the top of the incubator. The temperature should be kept at that required by the eggs at the level at which the eggs are kept. In order to monitor this, a thermometer should be placed at the same level as the eggs.
• N.B. the temperature will fall when the door is opened to add, remove or manipulate eggs. These procedures should be carried out quickly but carefully.
• For normal development, eggs must be maintained within a narrow temperature range. Both too high and too low temperatures may be deleterious to eggs, although in general eggs are more tolerant of low than high temperatures:

• A temperature which is too high by a few degrees may be lethal and even a rise of just 1.0-1.5C (2-3F) may cause embryo death after perhaps four or five days.
• Temporary cooling (as may occur naturally when an incubating bird leaves the nest to eat etc.) does not appear to be deleterious.
• Constantly slightly low temperatures may result in slow development and late hatching, but if the temperature is maintained at a sufficiently low level, deaths may result.
• Incorrect temperatures also affect incubation time, with earlier hatching if the temperature has been slightly high, later hatching if the temperature has been slightly low.
• See: Early-Embryonic-Death, Mid-incubation Embryo Death, Dead-in-Shell, Hatching Problems, Congenital Abnormalities

Humidity:

• Humidity levels can be measured with a wet-bulb thermometer.
• A wet-bulb thermometer is an ordinary thermometer in which the bulb is kept damp by means of a "wick" of covering the bulb and dipped into a small container of water. Evaporation from the wick reduces the temperature of the thermometer bulb.
• Since evaporation is greater in a drier environment, a lower temperature reading indicates a lower humidity and a higher temperature reading indicates a higher humidity. A dirty wick gives a falsely high reading. The distance from the thermometer to the water reservoir for the wick should be about one inch (2.5cm).
• Relative humidity is proportional to the wet bulb reading if the dry bulb reading is constant. Tables indicating relative humidity for different wet bulb readings at different dry bulb temperatures are available in some incubation texts (e.g. B42, B115.4.w1, B139).
• All incubators contain some method of maintaining humidity. Humidity is usually manipulated by changing the surface area of water trays placed in the bottom of the incubator - a larger surface area will produce a higher humidity. For example, trays may have a sloping floor, in which case increasing the depth of water will increase the surface area. Alternatively, surface area may be increased by placing sponges into the water with part of their surface coming out of the water.
• N.B. humidity will drop when the incubator is opened and , particularly in a still air incubator, may take some time to return to the previous level. Spraying the floor of the incubator lightly with water before closing the incubator door may be used to increase the rate at which humidity is restored.

Weight loss during incubation:

• Eggs normally lose a total of 18% of their weight during incubation, due to loss of water vapour which diffuses across the egg shell (J55.76.w1). Eggs should lose 15% of their weight from the start of incubation to the start of hatching (internal pipping). Monitoring and if necessary manipulation of their weight loss may be used to improve hatching success.
• For ideal results, each egg should be weighed individually on an accurate balance and the actual weight loss plotted on a graph and compared with the ideal weight loss for that egg. This may be done by hand or using an appropriate computer programme.
• Weight loss may be too fast due to thin shells or low incubator humidity. Weight loss may be too slow due to thick shells or high incubator humidity.
• If weight loss is too fast or too slow, it may be manipulated. N.B. Correcting the rate of weight loss after the first third of incubation is much more difficult.
• The correct rate of weight loss early in incubation appears particularly important for hatchability; incorrect early rates of weight loss may be fatal to the embryo despite later correction giving the required overall weight loss.
• If several incubators are kept at slightly different relative humidities, an egg may be moved into an incubator at higher humidity if it is losing weight too fast, or lower humidity if it is not losing weight sufficiently fast. Other methods involve altering the porosity of the egg shell:

• Porosity (and therefore water loss) may be increased by careful thinning of the eggshell using sandpaper.
• Conversely, part of the eggshell may be painted over with nail varnish to decrease water loss through the shell. 
• In extreme cases of excessive weight loss, rehydration may be used. This involves completely submerging the egg in cold (approximately 10°C, 50°F) sterile water for up to five minutes daily or even more frequently, with accurate weighing to monitor the uptake of water during the procedure. The cold temperature causes the egg contents to contract, drawing water into the egg. The frequency and duration of dipping should be varied according to the degree of weight loss and the stage of incubation. Care must be taken not to over stress the embryo by dipping for too long. Dipping in antibiotic solution has been described for the first dip (3mg tylosine tartrate (Tylan Soluble, Elanco Animal Health) in 1 litre sterile 09% saline giving 3000 parts per million tylosin solution). (B42, B115.4.w1, N1.92.w1).

• N.B. in general, eggs which are normally incubated in very damp conditions are likely to require a higher level of humidity during incubation than eggs which would be incubated in the wild in very dry conditions.
• See: Early-Embryonic-Death, Mid-incubation Embryo Death, Dead-in-Shell, Hatching Problems

Turning:

• Either automatic or hand turning may be used.
• If eggs are turned by hand they should be turned several times per day (minimum five times daily), and always turned an odd number of times so that the egg is on opposite sides for the longest internal (overnight) on alternate nights.
• Eggs should be marked with "O" on one side and "X" on the opposite side, and all turned so that the "O" is uppermost on all the eggs after one turning and the "X" is uppermost after the following turning.
• Eggs should be turned in one direction one day and the other direction the following day (i.e. rotated along their long axis clockwise and anticlockwise alternately). Continual rotation in the same direction may lead to problems such as twisting of the chalazae, rupture of the yolk sac or rupture of blood vessels in the embryo.
• Various means of automatic turning may be used. Eggs may be laid on their sides on rollers which move one way then the other alternately, or on a flat tray with movement provided by the movement of rods one way then the other (or the rods may stay still while the tray moves). An alternate method involves eggs being placed small end downwards in trays which are tilted to 45 degrees one way then 45 degrees the other way.
• N.B. if automatic turning is used, monitoring is required at different times of day to confirm that the eggs are being turned.
• See: Early-Embryonic-Death, Mid-incubation Embryo Death, Dead-in-Shell, Hatching Problems

Ventilation:

• Developing embryos require a flow of air to provide oxygen for respiration and to remove carbon dioxide.
• Rigid egg trays with an open mesh construction should be used to allow air to flow around the eggs and the addition of extra obstructions to air flow should be avoided.
• N.B. Air flow is lower in still air than in forced-air incubators and it is important not to overcrowd the eggs.
• The movement of air in an incubator containing eggs will be different from in the same incubator when empty, which is one reason why the incubator function should be checked with bantam eggs.
• Temperatures within the incubator may fluctuate if air flow is obstructed. If this cannot be rectified it is important to place eggs only in the most stable temperature areas of the incubator.
• See: Early-Embryonic-Death, Mid-incubation Embryo Death, Dead-in-Shell, Hatching Problems

Monitoring development:

• The development of the embryo within the egg is monitored most commonly by means of candling - shining a bright light through the egg (see: Candling). Candling is difficult if eggs have a very thick or patterned shell.
• Eggs may also be tested by Egg Floatation. The egg is placed in a bowl or bucket of water. Fresh eggs will sink, late-incubation eggs will float and live eggs close to incubation can be seen to move.

Hatching Facilities:

• A higher humidity is required for hatching and a separate incubator should be maintained for this purpose. High humidity is very important to avoid the shell membranes drying out, sticking to the chick and being unable to turn properly and push its way out of the shell. Either a still air of a moving air incubator may be used as a hatcher. N.B. frequent opening of the incubator , by lowering humidity, may result in hatching problems. A hatcher with a clear top or panel is useful to allow monitoring of hatching without constant opening of the hatcher.
• Hatchers tend to get dirty rapidly with bits of fluff, shell, etc. Frequent cleaning and sterilization is recommended, preferably after the hatching of each chick or batch of chicks. If chicks are hatching daily, two hatchers may be used, so that eggs may be in one hatcher while the other is being fumigated. If fumigation is not used, hatchers may be disinfected with a disinfectant of suitable efficacy and safety for use with eggs.
• Chicks may be hatched inside individual plastic boxes within the hatcher. This will reduce contamination of the hatcher with fluff, bits of eggshell etc. and also allows easy monitoring of which chick has hatched from which egg.
• See: Dead-in-Shell, Hatching Problems

Records:

• Accurate and detailed records are very important in incubation.
• In addition to records of individual eggs (see above: Introduction and General Information) it is important to keep records of the temperature (dry bulb) and the humidity (from wet bulb) of each incubator, so that increases or decreases in temperature or humidity are detected early and can be corrected.
• Trends in temperature and humidity may be most easily seen if plotted on a graph.

(J23.29.w1, B12.5.w10, B37.x.w1, B42, B106, B115.4.w1, B119.w1, B139, V.w5)

• Waterfowl eggs vary considerably in size (e.g. 25 grams for a teal egg, versus around 300g for a swan egg) and in the normal environmental and climatic conditions under which they would be incubated. Correctly controlling incubator conditions (temperature and humidity) for all the different eggs may be challenging (N1.89.w1)
• Hatching success may be improved by using parent or broody incubation for the first ten days. Conditions in the early stages of incubation are more critical than late in incubation.
• For waterfowl eggs, incubated at 99.5°F dry bulb temperature, with a wet bulb reading of 84°F, giving 55% relative humidity is suggested as a starting level (B42).
• Incubation conditions for waterfowl eggs of 37.2°C (99.0°F) dry bulb temperature and 31.1°C (88°F) wet bulb temperature, with a hatcher at 36.9°C (98.4°F) dry bulb, 31.1-32.2°C (88-90°F) wet bulb have been suggested (J23.29.w1).
• A separate hatching incubator should be used with a high (90-100%) relative humidity, preventing the eggshell membranes from drying. Downies should be left in the hatcher until they are dry.
• See: Early-Embryonic-Death, Mid-incubation Embryo Death, Dead-in-Shell, Hatching Problems, Congenital Abnormalities

(P3.1987.w1, V.w5)

• Hatching may need to be assisted, with care, checking the blood has been absorbed from the membranes and that the yolk has been absorbed, and keeping the membranes damp at all stages (see: Hatching Problems, Management of Hatching Bird Eggs) (B41, V.w5).

• Candling
• Egg Floatation
• Formaldehyde Fumigation of Incubators
• Management of Hatching Bird Eggs