It is not unusual for beginner and novice cockatiel breeders to misunderstand the topic of
linebreeding and inbreeding.  Often times I’m asked, “What is the closest a cockatiel could be
related to another cockatiel without producing genetic defects or lethal factors?

To answer that question we must first define inbreeding.  Among the stricter proponents,
Copyright © 2003 Linda S. Rubin
All Rights Reserved


A paper presented at the 2004 Bird Clubs of Virginia convention &
The 2004 American Federation of Aviculture convention.

It is not unusual for beginner and novice parrot and cockatiel breeders to misunderstand the
topic of linebreeding and inbreeding. Often times I’m asked, “What is the closest a cockatiel
could be related to another cockatiel without producing genetic defects or lethal factors?

To answer that question we must first define inbreeding. Among the stricter proponents,
inbreeding includes pairings such as parent to offspring, sibling to sibling, and half-sibling to
half-sibling.  A less strict definition confines inbreeding to brother-sister pairings only. This
article will refer to inbreeding as the breeding of brother to sister pairings.

Some readers may be surprised to learn that the closest genetic breeding is to mate brother
to sister.  Genetically, brother to sister pairings are the most identical to one another, closer
even than to their own parents.  Because each sibling inherits half its biological genome (all its
genes) from its sire, and the other half from its dam, each chick shares nearly the same
identical genes as its sibblings.

By comparison, a son paired to its own mother would share only half its genes with its dam;
similarly, a daughter paired to its own father would share only half its genes with its sire.  
Because full siblings carry genes from both their parents, brothers and sisters would share the
greatest number of genes in common.

Now, with that being said, it is best understood that most hobbyists should never breed brother
to sister pairings, most of the time, in the majority of circumstances.  Although special
conditions do exist where inbreeding may be permitted, they are better intended for the
advanced champion breeder and never for the inexperienced to experiment with.

Unfortunately, it is often the beginner or novice breeder who unwittingly or unknowingly
dabbles the most in inbreeding! For example, siblings bred from one pair may take advantage
of breeding with one another; or, the hobbyist may allow full or half siblings to breed, not fully
understanding the dangers and consequences of such unions.

Inbreeding should only be undertaken in a well-established linebreeding program where the
aviculturist has many years - often more than a decade - of background knowledge and
experience or fully understands exactly what is to be accomplished by the union. Ideally, a
planned inbreeding trial is carried out with the express purpose of introducing a new
characteristic into an existing, established line.  The goal of the inbreeding trial is to set an
identifiable characteristic (e.g., a new color or superior show trait) into a line in order to create
a new strain, embedding this characteristic within an already developed aviary stud.

However, in inbreeding practices, not only will all the superior, (positive), recessive traits rise
to the surface; inbreeding will also force all the inferior, (bad), recessive traits to the surface.  
By trait, I am referring to any inherited gene for color, shape, size, personality, fertility,
parenting skills, immune system, health, or any other visible or invisible characteristic.  There
are countless traits that are inherited through the genes of an individual bird. Although this
process also applies to linebreeding, it is even more intense in inbreeding practices.

So why breed brother to sister?  Brother to sister matings can be attempted under very special
circumstances such as setting a particular trait into proven, pedigreed champion or grand
champion stock where the seasoned aviculturist fully understands the benefits and risks
taken.  However, serious culling of the stock is necessary, usually by selling off as pets any
undesirable birds produced.

In informed inbreeding practices among seasoned breeders - contrary to horror stories - not
all young produced are hideous, monster chicks!  Unfortunately, frightening stories about
inbreeding among humans, or inappropriate pairs of animals that are not suitable candidates
are what abound.  The taboo is necessary among humans, but not among all animal pairings.  
Livestock husbandry is based upon linebreeding and occasional inbreeding practices.
In fact, if superior champion birds are used it is possible to produce a highly valued trait.  
However, simply pairing a brother-sister combination merely because they are “champion
stock” does not guarantee this result!  One must know precisely what the goal of a union is
and which trait is sought.

There can also be special exceptions necessitating inbreeding such as when there are no
other relatives available, or when attempting to quickly prove a new color mutation.  However,
even then it would be safer, and more preferable, to breed back to a parent because parent
and offspring share only half the genes as compared to full siblings.

An emphasized word of caution, however.  There is usually little need to breed this closely if a
more patient, planned breeding program is used and other family members are substituted.  
Even in the case of a new color mutation, the inpatient frenzy to dive in headfirst without
understanding the repercussions of lethal factors and complications (such as the loss of size,
vigor and vitality and other health issues) can create serious problems.  In the long run, a
healthy, robust line can be formed over several generations if a responsible, carefully crafted,
linebreeding plan is adopted.

So, what can happen when breeding brother to sister pairings?  For the majority, inbreeding
can result in lethal factors such as producing a preponderance of dead in shell babies, chicks
failing to thrive or that may die prior to weaning, inherited health problems, weakened immune
systems, and any number of outward physical maladies, conditions, or show “faults” we wish to
avoid.  Yes, there can be a time for inbreeding, but it is usually reserved for superior quality
birds raised by well-educated and experienced aviculturists.

Fortunately, however, there are other methods to use in order to establish an aviary stud.  
Linebreeding techniques, the use of less closely related relatives, are both useful and
necessary whenever building or maintaining breeding studs. In fact, without linebreeding
related birds, you won’t develop a strain or stud of your own!

Why use linebreeding programs?  Because the improvement of our birds is based on livestock
husbandry principles that outline planned, linebreeding techniques, and sometimes even the
sporadic use of inbreeding IF it is advantageous to the line.  If you are at all interested in
establishing your own aviary stud that perpetuates valued characteristics from generation to
generation, then linebreeding is absolutely necessary.  In order to create family lines and
develop different strains of birds that excel in specific characteristics, be it show qualities,
health, personality, parenting skills, or anything else, linebreeding is essential.

Linebreeding enables the aviculturist to create individual family lines, develop different strains
and bring them together to form a unique aviary stud.  The purpose of linebreeding is to set
selected, desirable traits into a breeding stud so that all birds will inherit these traits as part of
their genotype.  In turn, these traits will be passed down to future offspring because they are
inherited within the line(s).  In well-worked studs, these traits can even become recognizable
as originating from a specific aviary, e.g., from "John Doe’s line of birds."  Some cockatiel
studs are known for producing outstanding traits or characteristics, such as very large size,
“steam-boat” crests, super-sized cheek patches, creative whistling ability, high fertility, devoted
parenting skills, and so on.

Because a unique, individual breeding stud cannot be created or maintained without the
practice of breeding related birds, top breeders and exhibitors routinely practice linebreeding.  
By only working with unrelated birds (known as “outcrosses”), you simply cannot establish or
set inherited traits into your lines. Such traits may be inherited in the short term but will be lost
if not bred back into the line.  Linebreeding is the only way to accomplish the setting of
desirable traits among a flock from generation to generation.

If you are truly dedicated to starting your own aviary stud, it is wise to keep only the very best
birds that you own - provided they outwardly show the qualities you wish to set in a future
stud.  Either keep your other stock separate to produce pets, or keep those dearest to you as
your own special pets but do not include them in your breeding program.

If none of your birds are of high quality, you may instead wish to start from scratch.  Most of
the time this is the easier route to undertake, because by buying only a few top quality pairs of
birds you will have the traits you need to work with right away.

Also, it is best not to purchase stock from more than two or three breeders to start.  The goal
is not to buy birds from everywhere and everyone, because you will end up losing the very
traits you purchased once you breed many unrelated birds together.  Unrelated birds act as
outcrosses and you will need a written plan as to why one bird is partnered to another, just as
you do with linebred birds.

It is imperative that the cockatiels you purchase are linebred from a top stud if you wish to
retain the genotypes (full genetic makeup) you are purchasing. Linebred birds will have
identifiable visual traits, (and invisible traits such as health, etc.), that have been bred into the
lines that are dominant from generation to generation.  These traits, when correctly paired,
should also work for you.  When selecting future stock, ask the breeder whether the birds are
linebred, then ask which traits are set into the line (e.g., head width, crest density, round
cheek patch, extended mask, high wing carriage, healthy immune system, high fertility rate,
etc.).  Any “set” or physically dominant trait should be visible to you or proven in offspring.

The best advice for any livestock breeder is to purchase the best birds you can afford to buy.  
This may mean starting with only two pairs of birds if they are all you can afford.  Or, if using
your own birds as foundation stock, you may have to breed several generations to produce
superior birds before crossing them back to relatives or ancestors in order to set the trait(s).

There are many different linebreeding programs from which to choose.  Some of the most
common are breeding the best opposite sex offspring back to its parent or grandparent.  This
type of breeding will establish a line based upon the best cock (father or grandfather), and/or
the best hen (mother or grandmother). Some breeding programs advocate pairing the best
cock to the best hen, then the second best cock to the second best hen, and so on. Because
it is taxing to allow hens to produce many eggs, it is also common to breed more than one hen
to the best cock in the aviary.  Depending upon the results, the best half-siblings produced
can then be bred back to either their parents, to one another, or used in more distant unions.

Once each line has been developed with set traits, the lines may be merged together so that
you create your own strain or collection of inherited, recognizable traits. If each strain is kept
separate, they can even act as your own outcrosses whenever necessary.  Eventually, over
time, you will have several strains from which to form your entire breeding stud.  There are
entire volumes published on livestock husbandry techniques that apply equally well to
aviculture and raising birds, and aviculturists will do well to consult them.

1) Do not buy from too many breeders.  Limit yourself to two or three seasoned breeders - you
may want to go to advanced breeders or judges who are continually successful on the show
bench.  Buying from too many sources is like trying to finish a jigsaw puzzle that has too many
pieces.  You will ultimately lose the picture because not all the pieces will fit the puzzle and
there will be far too many pieces left over.

2) Buy linebred birds. It is better to buy good quality, linebred birds that you know have set
characteristics and a detailed pedigree illustrating the success of its family line, than to buy
unrelated outcrosses, no matter how lovely the birds may appear.  First, you can only guess
about the history of an outcross and whether any good qualities are set as dominant traits.  
Second, you won’t know whether the outcross has any lethal factors set as recessive traits.  
Once your breeding program is at a certain point, you will need to bring in an unrelated
outcross.  However, you can buy a bird from another linebreeding program so that it acts both
as an outcross, yet still guarantees (as a linebred bird) to set the necessary missing traits
back into your line while invigorating your stock!

3) Recognize that you get what you pay for!  Understandably, accomplished breeders who
have carefully linebred birds for generations, providing top nutrition and selectively breeding
for health, visual, and other qualities, are going to set higher prices than what you may find at
most pet stores or from a less knowledgeable breeder.  Supply and demand - it's purely the
economics of the situation. If a beginning breeder doesn't wish to pay top dollar for linebred
birds, then they may prefer to take the much more patient path and create their own.
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Dr. Rainer R.
"Well, there is help on
the horizon and
anyone seriously
interested in color
genetics should take
a look at Linda
Rubin's book:

Though this book is
primarily directed to
breeders of cockatiel
mutations, there is
enough information in
this volume to teach
anyone the secrets of
dealing with
recessive, sex-linked,
and dominant
ACBM, Vol. 65, No.12
112 pages, 15 chapters,
glossary & more!
Copyright 2006 Linda S. Rubin