Inbreeding in bird breeding: understanding the coefficient
The inbreeding coefficient measures the probability that both copies of a given gene in a bird are identical because they descend from one and the same ancestor, present on both sides of its pedigree.
A measure more than a century old
The formula used today in every breeding operation, whatever the species, was published by the geneticist Sewall Wright in 1922. It is not concerned with the number of common ancestors but with their position: an ancestor appearing on both the father’s and the mother’s side weighs more heavily the closer it sits to the parents.
A brother and sister paired together give a coefficient of 25 percent. Two first cousins, 6.25 percent. The same ancestor five generations back counts for almost nothing.
What the figure says, and what it does not
A high coefficient does not announce disease. It announces an increased probability that rare, recessive versions of a gene end up paired and are therefore expressed. That is the mechanism of inbreeding depression: declining vigour, reduced fertility, fewer hatchings, defects appearing without warning.
Conversely, controlled inbreeding remains a breeder’s tool. It fixes a trait, a mutation, a type. Many recognised bloodlines were built that way. The difference between the two comes down to one thing: knowing where you stand.
The short pedigree trap
This is the point breeders most often discover too late. A coefficient is only worth the depth of the pedigree it can see. Calculated over three generations, it cannot see the common ancestor sitting in the fourth: it therefore displays a reassuring 0 percent.
That zero does not mean “no relationship”. It means “no relationship visible in what I know”. Two birds shown at 0 percent over three generations may perfectly well be half-brother and half-sister one rank further back.
It is also why a coefficient calculated on a deeper pedigree often rises: the relatedness has not changed, only your view of it.
What this changes in AviarySoft
The application calculates the coefficient using Wright’s formula, from the parentage you have entered, and displays a five-level colour code before you form a pair.
The depth of the tree is therefore a setting that matters, not a display detail. It determines what the calculation can see. Parentage is also traced only through standard pairs, one identified male and one identified female: in a polygamous group, the application cannot determine which parent is which, and says so rather than guessing.
How does the Genealogy page work?
The Genealogy page offers four views of the same bird, which you pick from a dropdown: the interactive tree (zoom, pan and minimap), the ancestry table where each bird faces its two parents, the descendancy list showing which partner each youngster came from, and the half-circle fan revealing empty branches at a glance. All four are handled the same way: a click recentres the view on a bird, a double-click opens its sheet, and a right-click offers both of those plus opening the pair it came from. A breadcrumb reminds you where you came from and takes you back to the starting bird in one click.
What is the fan view for?
The fan shows ancestry as a half-circle, one generation per ring. Its strength is revealing empty branches at a glance: sectors with no bird immediately point to where your genealogy is incomplete, and therefore which records to complete first. You choose what appears in each sector, ring, birth year or plumage colour, depending on the room available.
How many generations can I view?
On the Free plan, the genealogy goes back up to 3 generations of ancestors. On the Premium and Pro plans, you reach the 4th generation (great-great-grandparents). The same limit applies both ways, towards ancestors as well as descendants. You adjust the displayed depth from the page toolbar, in each of the views.
How are parents linked in the tree?
Parental links go through breeding pairs. Only standard couples (1 identified male + 1 identified female) allow genealogy tracing. For polygamous or complex groups, the tree displays 'Not traceable' as the app cannot determine which parent is which.
How does inbreeding detection work?
AviarySoft automatically calculates the inbreeding coefficient (COI) using Wright's formula, the standard in animal genetics. The calculation analyzes common ancestors between the sire and dam across all visible generations, taking into account the inbreeding of the ancestors themselves. The result is displayed with a 5-level color code: negligible (0%, green), low (< 6.25%, green), moderate (6.25-12.5%, amber: first-cousin threshold), high (12.5-25%, orange: half-siblings) and critical (>= 25%, red: full siblings).
What is the inbreeding coefficient (COI)?
The COI (Coefficient of Inbreeding) measures the probability that two alleles of the same gene are identical by descent. A COI of 0% means no common ancestor was found between the parents. A COI of 25% corresponds to a sibling cross. The higher the coefficient, the greater the risk of inbreeding depression (reduced vitality, lower fertility, genetic defects).
What do the inbreeding risk levels mean?
AviarySoft uses 5 levels based on standard biological thresholds (Wright's formula): Negligible (0%, grey): no common ancestor detected. Low (< 6.25%, green): acceptable, no special precautions needed. Moderate (6.25-12.5%, amber): first-cousin threshold, monitoring recommended. High (12.5-25%, orange): half-siblings or grandparent/grandchild, not recommended. Critical (>= 25%, red): full siblings or parent/child, strongly discouraged.
Does the inbreeding coefficient appear outside the genealogy?
Yes, in three places. On the bird's sheet, where its own coefficient is shown. While you build a pair, where the app tells you in advance what the coefficient of the future youngsters would be. And on the Statistics page, which gives the average across your flock. When the known ancestry is too incomplete to conclude, the app says so explicitly instead of showing a reassuring zero.
Does the number of generations affect the inbreeding calculation?
Yes. The calculation analyzes common ancestors across the number of generations displayed in the tree. With 3 generations, the calculation is already reliable for detecting close crosses. With 4 generations (Premium and Pro plans), detection is even more accurate as it can identify more distant common ancestors.
Can I export the family tree?
Yes, Premium and Pro users get two vector PDF documents, therefore crisp in print: a landscape pedigree certificate and a portrait descendancy report by pair. They are generated from your data and not by capturing the screen, and are available from your phone as well as your computer. Exporting the view as a PNG image is still available. The export buttons are visible but disabled on the Free plan.
How do I get a printable pedigree certificate?
From the Genealogy page, the export offers a landscape pedigree certificate, generated from your data and not by capturing the screen. The document is vector, therefore crisp in print whatever the paper size. A portrait descendancy report by pair is available in the same place. Both are reachable from your phone, and reserved for the Premium and Pro plans.
What information appears on tree cards?
Each bird in the tree shows: ring number, name, species, breed, color, status, birth date, gender and photo if available. Exhibition results (scores) also appear on cards for the first generations. The further back the ancestor, the less information is displayed due to space constraints.
Can I customize the tree display?
Yes, and each view has its own settings, available from the page's settings panel. The tree lets you turn on or off the connection lines between generations, the inbreeding indicator, the legend, the information panel and the minimap. The descendancy list picks its columns, up to age and number of youngsters produced. The fan decides what fits in its sectors: ring, birth year or plumage colour. The displayed depth can be set in every view.
Can I see a bird's descendants?
Yes. The Descendancy view of the Genealogy page lists the children, grandchildren and great-grandchildren of the bird, showing which partner each youngster came from, with columns you choose, up to age and number of youngsters produced. The interactive tree can also extend to the right to show descendants next to ancestors.
How are descendants organized in the tree?
Descendants are grouped by breeding pair. A coloured banner shows which partner the youngsters came from (blue for a male, pink for a female), and clicking the union title opens the pair's sheet. If a bird has had youngsters with several partners, each group is clearly separated. For polygamous or complex pairs, the banner reads 'Multiple parents'.
How many generations of descendants can I display?
You can display 1 to 3 generations of descendants (children, grandchildren, great-grandchildren). The number of generations can be adjusted in the Genealogy page display settings. If a couple has more than 20 direct offspring, only the first 20 are shown with an indication of how many remain.
Are descendants included in PNG/PDF exports?
Yes. The descendancy report is a PDF document in its own right, organised pair by pair. In the PNG export of the tree, descendants are included as soon as their display is enabled: the generated image contains the complete tree, ancestors on the left and descendants on the right of the bird.