Definition of Fostering
Fostering is a rearing technique where eggs or chicks are taken away from their biological parents and placed under the care of another pair of the same or a different species.2
Reasons to Foster
Fostering may be used to establish an exotic species,1 to rescue chicks or eggs in the event that the biological parents cannot adequately care for them, or to increase productivity of the parent birds by stimulating them to start another clutch once their eggs/chicks are removed.1,2 If you are going to use fostering as a means to increase production, you should still limit your egg-laying hens to three clutches per breeding season so that the demand on the hen's body does not become too great. Likewise, you should limit your foster pairs to three clutches per season since chick rearing is such a demanding job.
Potential Disadvantages of Fostering
Several problems may result from fostering (or attempting to foster) gouldians. First, foster parents might not accept the eggs and chicks which are placed in their care.2 Second, if you are fostering chicks because their biological parents lack the requisite rearing skills to care for them, you may be inadvertently placing a selection pressure on that undesirable trait. A gouldian's ability to raise its own young is a skill which may not be solely a learned behavior, but have a genetic basis. By fostering the young from an unreliable pair, you are artificially selecting for what nature is attempting to select against: poor parenting skills.
Two other problems may arise due to fostering, but these issues are typically only caused by fostering gouldian chicks to a different species (such as society finches). First, certain infectious agents may be passed from society finch foster parents to the gouldian chicks that they are raising.2 These diseases can be fatal to fledging gouldians, as is the case with cochlosomosis and Campylobacter spp. infections.3
Society finches may be asymptomatic carriers of both of the pathogens responsible for those diseases.3 (On the other hand, society finches can prevent the spread of air sac mites when fostering gouldians because they are not susceptible to those parasites.3)
The second problem caused by fostering gouldians to a different species is an increased risk of imprinting.1 Once a chick has imprinted upon its foster parents, it may prefer to associate more with the species which raised it than it would with other gouldians. This can lead to problems later on, because the imprinted gouldian may refuse to breed with members of its own species.3
In order for a gouldian chick to imprint upon its own species, it must be exposed to other gouldian finches from the 15th to the 40th days of life.3
How to Foster
Step 1: Select an appropriate pair of foster parents.
Society (aka Bengalese) finches are the most commonly used (and will breed year-round), but zebra finches or even another pair of lady gouldians may also work. The foster parents should be chosen based on their parenting skills and not their color mutation.1 If time permits, allow unproven pairs to raise a clutch of their own chicks; doing so will allow you to evaluate their potential as foster parents.1 Using a second pair of gouldians as foster parents is ideal because imprinting no longer becomes an issue. Regardless of the species you select as foster parents, make sure that the birds you choose are healthy and free of protozoa, bacteria, and other pathogens that may cause illness or death in the chicks.
Step 2: Synchronize the breeding of the foster pair with the breeding of the parent birds.
In order for most potential foster parents to accept eggs or chicks from another pair, they need to be on the same page as the birds they are accepting eggs/chicks from. The foster pair must be set up for breeding to stimulate nesting behavior at or around the same time that the parent birds begin to breed. For best results, house each foster pair in their own enclosure. This is especially important for society finches who often prefer socializing with other munias (when given the option) over breeding. Note that in some cases, a trio of male society finches may successfully foster chicks, but the greatest success is usually gained by using a male-female pair of societies. You may need to set up multiple pairs for fostering1 to increase your chances for success. Be sure to feed your foster pairs an adequate diet for breeding just as you are feeding your gouldians for breeding.
Step 3: Transfer the eggs/chicks from the biological parents to the foster pair.
If transferring eggs, allow the biological parents to finish the clutch before you move the eggs into the foster pair's nest. This will improve the chances of the eggs hatching on the same day, which enhances the hatchlings' survival. Replace the foster pair's eggs with the eggs from the gouldian pair(s). Each foster pair should only have 4-6 eggs to care for at a time. Too few eggs in the nest may not be enough stimulation or encouragement for the foster pair to begin incubation, so use additional dummy eggs if necessary. On the other hand, too many eggs in the nest are cumbersome and will hinder successful incubation. If possible, only foster fertile eggs. You will need to candle the eggs after they have been incubated by the fosters for several days to make sure that they are still developing correctly. You may also wish to mark the fostered eggs in some way (with a nontoxic marker or dull #2 pencil) to indicate which biological pair they came from. Society or zebra finch eggs can be left in the nest to be incubated along with the fostered gouldian eggs (as long as no more than six eggs are present in total), however the parents may preferentially care for their own chicks over the fostered chicks, so it is generally advised to avoid fostering multiple species to a given pair at a time.
If transferring chicks, try to place the chicks in another nest which already has chicks of the same species and of a similar age in it. This is especially true for cases in which only a single chick needs to be fostered; adding a single chick to a nest with other chicks of a similar age will yield the best results (parent birds may not feel stimulated to feed just one lone chick). You may also be able to transfer newly hatched chicks to a foster pair which is "sitting tight" on eggs; this tends to occur when a pair is late in incubation and expecting the eggs to hatch soon. Replace some of the foster eggs with the newly hatched chicks. Transferring older chicks to a nest which only has eggs in it may not work (although it is worth a shot if no other options are available). If the fosters refuse to accept the older chicks, you may have to hand feed them. Once again, each foster pair should be limited to raising six or fewer chicks at a time. Any more than six chicks in the nest may be too much demand for the foster pair to keep up with.
Step 4: Monitor the foster pair.
Keep an eye on the foster pair and the eggs/chicks they are caring for. If necessary, intervene and hand feed chicks or try switching eggs/chicks from an unreliable foster pair to another pair. Remember to feed your foster pair for breeding just as you would the biological pair; the higher plane of nutrition will allow the parents to provide the chicks with an adequate diet for growth.
Avoiding Problems with Fostering
Problem: Not enough eggs are present to stimulate incubation.
Solution: Try adding dummy eggs to the clutch to increase the number of eggs present under the birds. Birds may not incubate if less than four eggs are present, or may have trouble incubating if more than 6 eggs are present.
Problem: Trying to foster gouldians to a trio of male society finches.
Solution: Because male society finches do not lay eggs, you may have to stimulate them to incubate by tricking them into thinking a clutch of eggs is being laid in their nest. Try adding a dummy egg to their nest each morning until a full clutch of 4-6 eggs is present. If they have begun incubating the clutch, you can swap the dummy eggs out for the fostered eggs.
Problem: Only one baby needs to be fostered.
Solution: One baby alone in a nest may not be a strong enough stimulus to get the parents (biological or foster) to care for it. Ideally, you should try to place this lone baby in a nest which has other babies of the same age and preferably of the same species. If this option is not available, you will probably have to attempt to hand feed the chick.
Problem: Fostering newly hatched babies.
Solution: If possible, transfer newly hatched chicks to a nest with other babies of the same species and age. If this option is not available, try adding newly hatched babies to a foster pair's nest with eggs that are being incubated "tightly." Remove all but one or two of the eggs and add the newly hatched chicks in their place.
Problem: Mixing species in a nest.
Solution: Although it is possible to transfer the eggs or chicks of various finch species to a pair of society (or zebra) parents,1 mixing species is generally not recommended if it can be avoided. Mixing species can be problematic because some species will grow faster than others, beg louder, and may outcompete the smaller, more quiet chicks. If, however, you need to mix species, just be sure to transfer eggs or chicks of the same 'age' to the foster pair. For example, if all eggs were laid around the same time, they will hatch at about the same time and reduce the risk of complications. Again, limit each foster pair to six eggs at a time.
Problem: Mixing chicks at different stages of development.
Solution: The best solution for this problem is to avoid it. Older babies may squish or outcompete younger chicks; they also fledge and wean sooner, which typically causes the parents to stop feeding the younger babies (at which point they will need to be hand fed). This is why timing is key: chicks must be of same age/size/etc. to be transferred to and raised successfully by the fosters.
Problem: The increased risk of imprinting.
Solution: In order for a gouldian chick to imprint upon its own species, it must be exposed to other gouldian finches from the 15th to the 40th days of life.3 This is not a problem for gouldian chicks which have been fostered under their same species, but may be a problem for gouldians which are fostered by societies (or zebras). Therefore if you are fostering to a different species, try keeping a cage of adult gouldians near the foster pair's cage, and place all newly weaned gouldian chicks in the same cage with the adult gouldians. In addition to this, keep all society (or zebra) finches out of sight and ear shot of the weaned chicks.1
1. Alderton, D. (1988). A birdkeeper's guide to finches. Blacksburg, VA: Tetra Press.
2. Olsen, G. H., & Orosz, S. E. (2000). Manual of avian medicine. St. Louis, MO: Mosby, Inc.
3. Tully, T. N., Lawton, M. P. C., & Dorrestein, G. M. (Eds.). (2000). Avian medicine. Oxford: Butterworth Heinemann.