Eggs (Including Clear Eggs & Egg Repair)
Introductory InformationMost of the time, a hen is stimulated to lay her eggs because she mated with a male. Sometimes, however, a hen may be stimulated to lay eggs even if no successful mating took place. Occasionally, a hen will even lay eggs if no male is present in her enclosure: she may pair off with another hen, or simply lay eggs without any stimulation from any mate at all. Of course fertile eggs will only result from a successful mating with a male, but the point is that sometimes hens will lay eggs even without the possibility of any of them being fertile.
That being stated, if you have a male-female pair of finches who has completed their nest and mated, you will most likely be seeing eggs arrive in the nest soon. Once a pair has copulated, a small percentage of sperm from the male's ejaculate is stored in special "sperm storage tubules" in the female's reproductive tract. She may store sperm there for up to about 16 days and release some of it as she ovulates. This helps to ensure that sperm is available to fertilize her ova when she is ready to lay her eggs. It also allows her to produce multiple fertile eggs days after the last mating took place. The important implication of this is realizing that a hen pulled from a cage with multiple males in it may be carrying the sperm of different cock birds for about two weeks (contrary to popular belief, even "monogamous" species will engage in extra-pair copulations). Therefore, if you have a specific mating pair in mind (Hen "X" with Cock "Y") and want to produce offspring from this pair alone, you will need to keep other cocks away from Hen "X" for at least a 16 days before introducing Cock "Y" to her for breeding purposes.
Once you have witnessed the pair mating, you should expect to see eggs in the nest within approximately 5-7 days. Finch eggs are laid once a day, usually daily and usually during the early morning hours, until a clutch anywhere from 3-8 eggs is produced (4-6 eggs most commonly).13 It would be wise to keep track of the date that each egg is laid (as well as the date on which incubation begins) for monitoring purposes, as explained later. Of course, make sure you are feeding an adequate diet and providing a constant source of calcium (such as a cuttle bone) to reduce the risk of complications such as egg binding. A video of a hen laying an egg can be found in the Video Documentation section.
Parental Care of EggsFertile eggs can survive for about one week before incubation commences. If incubation does not begin within a week of an egg being laid, its hatchability decreases significantly. Parent finches normally begin incubating their clutch after the 3rd-4th egg is laid,13 although some pairs will wait until the clutch is complete to begin incubation. You will know incubation has begun when at least one of the birds is sitting on the eggs, not only during the day, but also at night. Usually both parents share the responsibility of incubation during the day. At night the hen alone usually incubates, although the cock may sleep next to her.13 Remember to record the date at which incubation begins, so you will be able to monitor the progress of the eggs. Please note that many pairs will not incubate their eggs unless at least three eggs are present in their nest.
Once incubation has begun, it should not be ceased (or the embryos will die). Eggs may be left unattended for brief periods of time (up to about 15-30 minutes), however, while the parent birds stretch their wings, or take a break to eat and drink. Parents instinctively know to gently rotate the eggs beneath them periodically as they incubate, which allows the embryos to develop properly. In addition to warmth, eggs require a certain humidity to survive. This can be accomplished by providing the parents with a bath (a shallow dish or bowl of water) so that they may moisten the eggs with their damp bellies after bathing. Incubation generally takes 12-16 days, depending on the species.13 The Species section has incubation times for each species listed separately.
Unfortunately parents do not always care for their eggs correctly. Some birds will accidentally puncture an egg (see below for methods of egg repair), and if the damage is bad enough, consume the egg. This is why it is important to clip the birds' toenails before they breed, and one of the reasons to only provide them with safe nesting materials. Other pairs suffer from other parenting problems: overzealous nest building may result in a nest with such a shallow entrance that eggs are accidentally knocked out ("tossed") and fall to the floor as the parents exit the nest. If these eggs break, the parent birds may eat them. Other overzealous nest builders may build a nest on top of an existing clutch, burying the eggs. Both of these problems can be solved by limiting the amount of nesting material available to your birds (if they seem to be the type suffering from this problem). Zebras are notorious for overstuffing their nests with nesting material; the nest should not be filled any higher than a half inch below the entrance to the nest. If your pair seems to suffer from "disappearing eggs," one of the above-mentioned scenarios is a likely culprit. Clipping toenails and limiting access to nesting materials should help prevent the disappearance of eggs from the nest.
If the parents do not seem attentive to the eggs, it may be wise to place the eggs under the care of foster parents or to incubate them artificially, as described below.
Performing Nest ChecksFinches, especially breeding finches, should not be disturbed unnecessarily. Hovering about and tampering with their nest makes most finches very nervous and my cause them to abandon their nest and eggs. Some finches, however, will tolerate occasional nest inspections, with some pairs tolerating nest checks better than others. Generally, the more domesticated the species, the more tolerant they tend to be. Zebras and society finches, for instance, usually allow nest inspections, while other more nervous species are better off left alone. If you have had a pair abandon their nest and eggs in the past, you should probably not risk nest inspections with that pair in the future.
That stated, occasional nest checks, when done correctly, can help you gain information about the status of the eggs. If you have set up the breeding cage with an external nest box that has a hinged top, you will be able to perform the easiest and least intrusive nest checks. Nests placed inside of the enclosure are more difficult to get to, so use your best judgment about whether or not inspecting those nests is worth risking the pair abandoning their eggs.
Ideally, you should only inspect a nest when both of the birds are outside of it. Hopefully the nest is eye level to you so that you can simply peer inside to see if eggs have been laid yet, and if so, how many have been laid. Try to avoid the temptation of hovering about a breeding pair's cage. The more privacy you can give your birds, the better. I recommend glancing into the nest from a distance (if possible) once per day while you are providing the birds with fresh food and water. Record the dates that you see each egg laid, and record the date that you notice the pair begin incubation.
If you need to reach into the nest for any reason (such as candling eggs for fertility as described below), make sure to wash your hands first, to be very gentle with the eggs, and to make the nest check as short as possible.
Candling EggsTo accurately tell if an egg is fertile or not, you must candle it. This is a somewhat delicate procedure in which a small light source (such as a small flash light or an "egg candler" like the one pictured to the right) is held up to an egg on or after the fifth day of incubation to see if any growth is evident. This is part of the reason why keeping track of the incubation start date is important. Do not attempt to candle eggs if this is your birds' first clutch or if your birds have a tendency to abandon their eggs upon being disturbed.
If you are going to candle, make sure you wash your hands thoroughly. You should also make sure the light source you are using is clean; good hygiene is a must when handling eggs. The candler should have a low-wattage (<< 40) bulb; too high a wattage can damage or kill an embryo.16 Candling is not easy to do in a well-lit room; if you can, dim the lights in the bird room or bring the nest into a room where you can set the lighting to low. Next, if you can, very carefully place your light source up to the side of one egg at a time while they are still within the nest. If you cannot easily maneuver your light source within the nest, you will need to CAREFULLY remove the eggs from the nest (without crushing or cracking them) and hold the light up to each egg outside of the nest. After you have evaluated the eggs, return them to the nest (and replace the nest in the enclosure if you had to remove it).
If an egg is viable, you will be able to see a network of small red blood vessels, and possibly see the developing embryo. The large end of the egg should contain an air pocket. On the fifth day of incubation, you may be able to witness the embryo's heart beating. Candling eggs which have been incubated longer than 5 days will show increased development: the blood vessels may appear larger and cover a larger area, and eventually the chick will fill up most of the space within the egg. You may be able to see the chick moving about inside of the egg as it grows larger. You should candle all of the eggs on day 5 and again on day 10 of incubation, to see if the eggs have developed further or if any embryos have died within the egg. If the eggs are still viable on day 10, you should see darkness (the chick) covering most of the inside of the egg.
Infertile egg Fertile egg Fertile egg
Infertile or "clear" eggs will appear empty except for a yellow yolk and the air pocket. Occasionally, an embryo will die at an early stage of life and nothing but a thin blood ring will be visible within the egg. Wait a few days and re-candle these eggs to be sure that they are not developing. Some breeders chose to eliminate these eggs, but doing so may run the risk of causing the parents to abandon the nest. Leaving at least 3-4 eggs in the clutch will encourage the pair to return to incubation, but there is usually no harm in leaving infertile eggs in the nest. You may wish to remove them a few days after any fertile eggs have hatched. If all of the eggs are clear, and remain clear when they are re-candled a few days later, they may be discarded. The pair will probably want to start a new clutch, but you should first address the reason that their eggs are clear before you let them attempt another clutch (see below).
To see what the inside of a fertile finch egg looks like at 5 days of incubation, place your mouse cursor over the image below:
Fertile Eggs: from Formation to HatchingA cock and hen copulate and the cock passes his ejaculate to the hen who stores some of his sperm in her reproductive tract. When the hen ovulates, some sperm is released. A spermatozoa only has a very short window of time to fertilize the ova, as albumen ("egg white") will be deposited soon, which blocks entry of the sperm. The fertilized ova (which has already begun its development into an embryo) travels through the reproductive tract of the hen, first receiving the added albumen, then the inner and outer shell membrane, followed by water and electrolytes, and finally the shell. The shell is created by calcium deposition around the forming egg within the uterus. The fertilized ova takes approximately 4 hours to travel to the uterus. Once in the uterus, calcification of the egg's shell takes approximately 20 hours. This is why a hen can only lay one egg per 24 hour period. About 15 minutes after the first egg is laid, the hen ovulates again and the process is repeated. This is why the hen lays a single egg at about the same time each morning until her clutch is complete.
Finches are never considered "pregnant," nor do they "carry eggs." Once the ova is fertilized and the egg is formed, it is laid (video) and the embryo's development is paused until incubation begins. Complications can occur at the time of egg laying, such as "egg binding," a condition where the hen has formed the egg but can not pass it. Egg binding is a serious condition which should be addressed immediately to save the life of the egg bound hen (see Complications & Troubleshooting). If the hen lays all of her eggs successfully, the pair will begin to incubate them (some pairs begin incubation after the third or fourth egg is laid while others wait until the clutch is complete). Assuming that the embryo is genetically fit, that the egg it is growing within contains adequate nutrition, that the egg is being incubated properly with the proper humidity, and that no bacteria, fungi, or viruses have infiltrated the egg, the embryo will resume development. At about day 5 it should be just large enough to be visualized during candling. By day 12-16 (depending on the species) the chick will be ready to hatch. If the chick has positioned itself correctly within the egg, it will use its small egg tooth to pip a tiny hole near the larger end of the egg (where the air sac is). The chick will slowly rotate its way around, pipping as it goes, until the "top" of the egg is freed and the chick emerges. Normally chicks need no assistance in doing this, and it is usually in the chick's best interest that you do not interfere with a normal hatching process. The chick may take from a half hour to well over 24 hours to complete the hatching process, depending on the species.16 The parents usually discard of the egg shell by consuming it. To learn more about the further development of hatched chicks, refer to Young (Hatchlings to Maturity).
Clear & Unhatched EggsIf an egg fails to hatch, one of two things must have happened: either the egg was never fertilized in the first place, or the egg was fertilized, but the embryo died before it was able to hatch. Each of these scenarios has many possible causes.
First consider the case of the unfertilized ("clear") egg. One suggested cause of unfertilized eggs is sexual inexperience.2,16 If birds are young or simply new to breeding, it may be possible that they do not yet understand all of the necessary motions that must occur for copulation to be successful. Another possible cause is inappropriate pairing of birds.2,16 If you accidentally paired two hens together, or if you paired incompatible birds of the opposite sex (which did not bond), they will not mate nor produce fertile eggs. Other poor husbandry practices may also inhibit a pair from successfully copulating, including: not supplying a proper nest, not providing stable perches (for those birds which mate on a perch), not furnishing the enclosure with adequate visual barriers between pairs, disturbing the birds or aviary excessively, pairing birds which are too young or too old to breed, incorrect photoperiod (for birds housed indoors), poor nutrition, and improper temperature, humidity, and so forth (correct environmental cues are important for stimulating many species to breed).2,16 Most of these problems can be overcome by improving one's husbandry practices. Unfortunately, however, other causes of infertile eggs still remain which may not be as easy (or even possible) to fix, as they are due to defects in the birds themselves. Although rare, sterility or infertility is a problem for some birds, both male and female, and may be due to genetic causes (as is the case with heavily inbred birds and most hybrids or "mules"), environmental causes (excessive heat, for instance), age, or disorders (such as infection or tumors of the reproductive organs).2,16 Additionally, any physical handicap which impairs a bird's ability to copulate will prevent successful fertilization of eggs.16 Examples of such disadvantages include lameness, obesity, and loss of toes.2
Sometimes eggs are mistaken for infertile when in fact they were fertilized but suffered from early embryonic death. The most common causes of early embryonic death are incorrect temperature, jarring of the egg, and lethal genetic traits.16 In most cases, early embryonic death cannot be visualized by candling of the egg. Instead, an egg necropsy should be performed to determine if the egg was infertile or if it in fact suffered from early embryonic death. The presence of a white blastodisc is indicative of an infertile egg, whereas the presence of a blastoderm and/or a blood ring (as pictured to the right) is indicative of early embryonic death. Your avian veterinarian should be able to perform the necropsy at your request. Breeding birds in a temperate environment and refraining from shaking the nest and eggs will help to ensure that early embryonic death does not occur. If you suspect that genetics are at fault, you might try to pair your birds with new (unrelated) mates.
Embryos do not always die during the early stage of their development. They may also die during the middle of incubation, usually due to nutrient defficiencies.16 In fact, eggs which are laid by a hen experiencing vitamin deficiency (as is the case with hens fed only unsupplemented seed diets) are expected to die in the middle third of incubation.6 Minor nutritional deficiencies will become magnified as the breeding season continues and the hen's body stores become even more depleted. Although bacterial or fungal infections may also cause an embryo to perish at this stage of development, they are more often responsible for late embryonic death.16
In addition to infection, late embryonic death may also be due to improper incubation (lack of proper temperature and/or humidity) or a genetic abnormality (mainly malpositioning at the time of hatch).16 Providing the parents with a clean nest, a clean cage, and only fresh, clean nesting material will help to prevent the introduction of pathogens to the eggs.16 It is also important that the parents be healthy at the time of breeding, and that no sick birds or fomites are allowed to come into contact with the parents or eggs. Hygiene and proper quarantine procedures are essential to successful breeding. Additionally, birds should be bred in an area which is free of toxins: nicotine, carbon monoxide, herbicides, insecticides and even some antibiotics given to parent birds can all lead to embryo fatality.16 If pairs are being treated with medication, wait until they are finished with the regimen to breed them.
In cases where eggs were fertilized but failed to hatch, an egg necropsy and culture of the contents should be performed by an experienced avian veterinarian to determine the probable cause, enabling you to make any needed adjustments to your breeding program to prevent further unhatched eggs. If a pattern of embryonic death is witnessed (e.g. 1/4 or 1/16 of the eggs die) and no other cause is found, suspect lethal genetic combiations.16 Also be aware that fertility and hatchability of the eggs varies with the age of the parents.16
Egg RepairFertile eggs with small puncture holes or thin cracks may be candidates for egg repair. The sooner you repair the egg after it has been damaged, the better. Before handling any egg, always wash and dry your hands. Eggs which have had their shell compromised are very susceptible to entry by pathogens which can kill a developing embryo. Good hygiene, therefore, is a must. Apply a very small amount of nontoxic elmer's white glue to a clean Q-tip and spread it gently and thinly over the crack or hole. (Surgical glue may be substituted for Elmer's). If the hole is too large to cover in this way, you may use a combination of elmer's glue and non-dyed tissue paper to patch the hole. Be very careful to only cover the smallest area possible with the glue, so that the rest of the egg shell can still breathe. If you clog too many of the tiny pores within the eggshell, the chick will suffocate. Allow the thin layer of glue covering the crack or hole to dry between coats, as several coats may be needed. Once the crack or hole is sealed sufficiently, allow the glue to dry and replace the egg in the nest. Hot dripped beeswax or paraffin wax may be used in place of glue16 (multiple coats are not needed, and it "dries" [cools] more quickly than Elmer's glue). If possible, try to complete the egg repair procedure within a half hour's time so that the egg may be returned to incubation quickly. In a few days, candle the egg to see if the chick is still developing or if it appears to have died. Please be aware that chicks which survive egg repair may need assistance during the hatching process, depending on the location of the glue or wax seal. If the seal is in the way of the pipping area, you may need to help the chick pip through it.
Artificial Incubation of EggsFirst and foremost, please understand that incubation of an egg is a very delicate and precise process. Embryos will only develop within a very narrow temperature range: at higher temperatures within this range, they develop more quickly, and at lower temperatures within this range, they develop more slowly. Temperatures outside of the range (by as little as a single degree Celsius) will result in embryo death.16 If an embryo develops too quickly, it may be too weak to hatch. If it does hatch, it will probably die because embryos which develop too quickly tend to suffer from a greater incidence of physical deformities (such as curled toes and scissor bills) and still have exposed yolk sacs at the time of hatch16 (under normal circumstances, the remainder of the yolk sac is drawn into the body prior to hatch and serves as an energy source for the first hours of life). If an embryo develops too slowly, on the other hand, it may suffer from a delayed hatch and an abnormal physical appearance.16 Therefore an embryo must be incubated at just the right temperature in order to develop correctly.
Temperature is not the only essential parameter in incubation, however. Humidity is also very important, and is most critical during the first third of incubation.16 If humidity is too low, an embryo will become dehydrated, possibly resulting in kidney failure and stunted growth.16 Likewise, if humidity is too high, the air cell in the egg will be small (if it becomes too small, the embryo will die late in incubation) and any chick which does hatch may have an exposed yolk sac among other physical abnormalities.16 Exposed yolk sacs at the time of hatch are problematic because they leave the chick more susceptible to infection; if a chick hatches with an exposed yolk sac, it should be rushed to your avian veterinarian for immediate correction.16
The third critical factor in incubating eggs is turning them. Doing this is necessary to prevent the contents of the egg from sticking to the inside of the shell. During natural incubation, parent birds will turn the eggs on average once every 35 minutes.16 For artificial incubation, turning the eggs an odd number of times between five and eight times a day should suffice.16 Not turning often enough may lead to embryo death (either early or late) among other complications.16 Additionally, eggs should not be rotated in the same direction each time, as this may lead to internal tearing of the membranes and embryonic death.2 Instead, alternate between rotating eggs 180 degrees, and then counter-rotating them 180 degrees during the next turning.2 Always be gentle and slow when turning eggs. Automatic egg turners may be purchased to fit most commercial incubators and egg sizes, and are preferable to manual turning of the eggs. If you are hand turning eggs, I find that it helps to use a nontoxic, fine-point marker to label one side of the egg with an "X" with an arrow pointing right and the other side with an "O" and an arrow pointing left.
Lastly, egg and incubator hygiene is a must. First, always wash your hands prior to handling eggs. Second, do not get eggs wet as this may remove the naturally protective cuticle which surrounds them.16 Third, clean and disinfect the incubator before and after each batch of eggs is placed within it.16 Lastly, clean and disinfect water trays (within incubators which have them) daily.16
With incubation requirements being so precise, it is impractical to attempt to build your own incubator at home. Simply stated, placing eggs under a lamp or attempting to hold them in the palm of your hand will not work. Instead, purchase a commercial incubator. Because such a purchase needs to be made well in advance (in order to purchase, receive, set up, and test that the incubator is functioning prior to using it), it may be advisable to invest in an incubator before you set your birds up to breed. This way, you will have a back up plan in case eggs need to be rescued or maintained until a foster pair can be acquired.
Commercial incubators should be purchased with temperature and humidity measuring devices (preferably two of each so that they may be standardized against each other2), an automatic egg turner, and humidity control (usually water pans located within the incubator). If you can find one, look for an incubator that is a "forced air incubator." Incubators of this type move hot air around, distributing it throughout the inside of the incubator, creating a more evenly heated environment.2 At least one finch enthusiast has had good success with the Turn-X incubator, as documented on eFinch.com.
Once you have received and set up your incubator, let it run for at least 30 days prior to placing any eggs inside of it.16 This will allow the temperature and humidity inside of the incubator to stabilize, as well as to allow you to make sure that it is functioning properly.2 You may wish to leave it running throughout the entire duration of the breeding season, so that it will be primed and ready in the event that eggs must be unexpectedly rescued or incubated for any other reason. Below you will find a table summarizing the parameters for incubating finch eggs, as well as a table for calculating relative humidity inside of an incubator using wet bulb readings (based on a dry bulb reading of 37.5° C [99.5° F]).
|Temperature||37.5° C (99.5° F)|
|Humidity||50-60% (wet bulb reading of 28.5° C [83° F] to 30.5° C [87° F])|
|# of Turns per Day (if manual)||5 or 7|
|Incubation Length||Varies per species (12-16 days on average, see Specific Species)|
|Calculating Humidity from Wet Bulb Readings (with Dry Bulb at 37.5° C [99.5° F])|
|Wet Bulb||Approximate % Humidity|
|28° C (82° F)||48|
|29° C (84° F)||53|
|30° C (86° F)||58|
|31° C (88° F)||63|
|32° C (90° F)||68|
|33° C (91° F)||73|
|34° C (93° F)||79|
|35° C (95° F)||85|
|36° C (97° F)||91|
|37° C (99° F)||97|
Once eggs are due to hatch (the egg has undergone drawdown or the chick has pipped), cease turning the eggs. This usually occurs 24-48 hours prior to the end of incubation (in other words, if a species is known to have a 16-day long incubation period, stop turning the eggs on day 14 or 15). The chick will rotate itself 360° within the egg, cutting as it goes until it opens the top of the egg and emerges. This may take many hours. Do not attempt to assist a hatch unless you repaired an egg and the site of repair is in the way of the chick's pip or cutting area. Several physiological changes are occurring as the chick hatches (see Anatomy), and assisting the hatch may interrupt these and lead to weakening of the chick. In most cases, assisting a hatch does more harm than good. If, however, you feel strongly that your chick is in need of assistance during hatching, call your avian veterinarian for advice.