The nest cycle
Pair an adult cock and an adult hen in a nest box (a bird is an adult at 50 days old). A pair raises one clutch and is then finished; you pair again for the next one.
| Stage | Days | What happens |
|---|---|---|
| Courting | 2 | The hen accepts or refuses (next section) |
| Bonded | 1 | The pair is together |
| Nest building | 3 | |
| Egg laying | 2 | 2 eggs are laid at the end; fertility is rolled |
| Incubating | 18 | At the end each fertile egg may hatch |
| Chick care | 28 | The parents raise the chicks. Hungry parents lose chicks. |
| Fledging | 0.2 | The young join your loft (if there is room) |
From pairing to the young leaving the nest is about 54 game days (roughly 1 hour 48 minutes of play). Nests keep running while the game is closed. Nest boxes: a loft starts with 1 and can open up to 4 (400G, 800G, 1,600G).
Source: scripts/breeding.gd.
Courtship
Drive and Affection are hidden traits of each bird (normal around 60, between 10 and 98), fixed by the bird. An average pair accepts 60% of the time. After a refusal the pair tries again; three refusals in a row end the pairing. The chance a normal pair bonds within three tries is 1 - 0.4^3 = 94%.
Auto pairing (a setting, on by default): each game day, if a nest box is free, there is a 30% chance that the best-matched free cock and hen that are not second cousins or closer claim it themselves.
Eggs and hatching
| Parents' Fertility | Fertile | x Hatch | = Chick per egg | Average chicks from 2 eggs |
|---|---|---|---|---|
| 38 + 38 (fancy rares) | 82.0% | 92% | 75.4% | 1.51 |
| 43 + 46 (mythic racers) | 85.3% | 92% | 78.5% | 1.57 |
| 55 + 55 | 90.5% | 92% | 83.3% | 1.67 |
| 62 + 62 (common flyers) | 94.0% | 92% | 86.5% | 1.73 |
- A clutch is always 2 eggs. If none hatch, the pair goes back to "bonded" and rests 4 days before the next cycle.
- Feed both parents on the day the eggs are laid: an unfed parent costs 20% fertility.
- During the 28 days of chick care, if neither parent is fed on a day, each chick has a 10% chance to die that night. One fed parent is enough.
- Fertility is the only stat that matters for eggs. The higher-rarity racing breeds are harder to breed (mythic base 43 against 62 for a common flyer).
Inbreeding
Every chick stores the ids of its ancestors for four generations (parents, grandparents, great-grandparents and one row further), so the game can tell how closely two birds are related. It counts every path to a shared ancestor: each path adds 1/2 to the power of (steps up from the cock + steps up from the hen + 1). That is the inbreeding coefficient of their chicks. The same ancestor on both sides more than once adds up, so a loft bred in a closed circle gets worse every generation. Birds with unknown parents (shop birds, strays) and ancestors further back than four generations count as unrelated. Old saves are filled in from the parents still in the save.
| Tier (shown in the pair screen) | Who | Coefficient | Strength | Accept | Fertile | Hatch | Chick stats | Chicks per clutch* |
|---|---|---|---|---|---|---|---|---|
| Close kin 25%: weak chicks | parent and child, full siblings | 25%+ | 2.0 | -20 | -40 | -20 | -8 | 0.73 |
| Near kin 12%: high risk | half siblings, uncle and niece, grandparent and grandchild | 12.5%+ | 1.0 | -10 | -20 | -10 | -4 | 1.15 |
| Cousins 6%: some risk | first cousins, half uncle and niece | 6.25%+ | 0.5 | -5 | -10 | -5 | -2 | 1.40 |
| 2nd cousins 1.6%: low risk | second cousins | 1.56%+ | 0.125 | -1.3 | -2.5 | -1.3 | -0.5 | 1.60 |
| Distant kin: tiny risk | third cousins and further (down to 4 generations) | under 1.56% | 0.03 or less | -0.3 | -0.6 | -0.3 | -0.1 | 1.65 |
| Unrelated | no shared ancestor | 0 | 0 | 0 | 0 | 0 | 0 | 1.66 |
Strength is the coefficient x 8 (at most 3.0) and the penalties are the old ones (accept 10 points, fertile 20 points, hatch 10 points, 4 on every chick stat) times strength; the points in the table are percentage points. A pair with three shared grandparents has coefficient 9.4%, strength 0.75, still "Cousins". *At FER 55 + 55, two eggs a clutch. The pair screen shows the tier in green (unrelated), amber (distant, second cousins), orange (cousins) and red (near and close kin). Auto pairing skips second cousins and closer.
The upside
Kin pairs also give steadier chicks that lean toward the better parent, scaled by the same strength: the random spread shrinks by 1.5 per strength (close kin: -3 to +3, near kin: -4.5 to +4.5), the weight on the parents' stats rises from 0.25 by 0.2 per strength, and the parents' value used moves toward the better parent by 50% per strength (fully at strength 2). Simulated (1,200 pairs, 6 chicks each, average of all stats, tools/sim_kin.gd): with ordinary parents the average chick is 63.6 unrelated, 61.9 for cousins, 60.3 for near kin and 57.5 for close kin, so it is a loss; with parents 20 points above a typical bird it is 68.6, 68.8, 69.2 and 70.4, a small gain for the closest kin, and the spread between chicks of one pair falls from 1.03 to 0.89, 0.78 and 0.52. Together with the lower fertile and hatch chances it is a gamble that only pays when both parents are strong. A big line of cousins is only a mild risk.
Show chicks suffer more: a bird whose grandparents repeat on both sides loses up to 10 symmetry points in the Fancy Show.
What chicks inherit
Breed mix
The chick's breed mix is the average of the parents' mixes, for each breed, with a random shift of 0 to 5 points between two of its breeds. Percentages are rounded and the biggest share takes the leftover so they add to 100. The breed with the biggest share is the chick's main breed; it decides the trait and the look the chick is judged on.
Stats
This is the most important breeding rule: a chick inherits only a quarter of how far its parents are above (or below) the breed's normal level. Two Janssens with speed 90 (breed base 76) give chicks around 76 + (90 - 76) x 0.25 = 79.5 (between 73.5 and 85.5). Chicks drift back toward their breed, so to get better birds you mostly need a better breed, and a lucky chick. The stats a chick can train in life are limited by potential, which also comes from the breed mix.
Look
- Colour and pattern: each is copied from the cock or hen with equal chance (50 / 50).
- Mutation: 6% for the colour and 6% for the pattern to be replaced by a random one of the 8 colours or 6 patterns (so any specific colour mutation is under 1%, and about 11.6% of chicks have at least one mutation roll).
- Sex is 50 / 50. The chick starts with bond 0 and clipped, and needs to bond to 100% before it flies.
Rarity and where breeds come from
| Rarity | Shop price | Sell multiplier | Vitamin dose | Breeds |
|---|---|---|---|---|
| Common | 80G | x1 | 40G | Slenderbill |
| Uncommon | 220G | x1.5 | 70G | Janssen, Van Loon, Tippler, Birmingham Roller, Modena |
| Rare | 600G | x2.5 | 100G | Houben, Meulemans, Budapest Highflyer, Oriental Roller, Serbian Highflyer, Classic Frill, African Owl, Turbit |
| Epic | 1,500G | x4 | 135G | Vandenabeele, Jan Aarden, Pakistani Highflyer, Satinette Frill, Fantail, English Pouter, Archangel |
| Legendary | 4,000G | x7 | 165G | Leo Heremans, Van Den Bulck, Budapest Tumbler, Blondinette Frill, Jacobin |
| Mythic | 10,000G | x12 | 200G | Jan Hooymans, Best Kittel Line |
| Rarity | Shop (per slot) | Stray (no lure) |
|---|---|---|
| Common | 45% | 55% |
| Uncommon | 28% | 25% |
| Rare | 15% | 12% |
| Epic | 7% | 5% |
| Legendary | 4% | 2.5% |
| Mythic | 1% | 0.5% |
- Shop: 4 birds a week (every 7 game days), each slot rolls a rarity and then a breed of it, and the same breed is not offered twice. The stock is the same for everyone who is on the same day number.
- Strays: after the rarity, a breed is picked; racing breeds count 0.35 (see what kind of stray arrives). Common is only Slenderbill, so over half of all plain strays are Slenderbills. The lure improves the odds.
- Breeding: a chick has the average of its parents' breeds, so crossing a rare breed with a common one gives a chick whose rarity is in between (it is sold and judged on the mix, see selling price).
Worked examples
Example 1: a clean clutch
A Janssen cock and a Van Loon hen (unrelated, Fertility 55 and 55), both fed. Courtship works 60% of the time per try. The 2 eggs are each fertile 90.5% and hatch 92%, so the chances are: 0 chicks 2.8%, 1 chick 27.8%, 2 chicks 69.4%. Chicks are 50% Janssen, 50% Van Loon (plus a drift of up to 5 points), and each stat is the average of the two breeds' base, plus a quarter of how far the parents are from that, plus or minus 6.
Example 2: siblings
A brother and sister from one clutch. Courtship drops from 60% to 40% (so 78% to bond in 3 tries); eggs are fertile 50.5% of the time, hatch 72% (36.4% a chick per egg); every chick stat is -8. The clutch gives 0.73 chicks on average and a 41% chance of nothing. Pair unrelated birds.
Example 3: Breeder mix
For a Fertility 55 + 55 pair, Breeder mix raises the chance of a chick per egg from 83.3% to 95.5% (fertile 95.5%, and every fertile egg hatches), the average clutch from 1.67 to 1.91 chicks, and gives each chick +1 on every stat. It costs 40G to 200G a dose, depending on the rarity of the bird it is given to. It is used up at hatching.