BYM or purebred?

Rathornis

In the Brooder
May 31, 2025
3
15
26
Short version: Is there a way to determine the breed of these chicks (Pure Australorp vs Australorp/BYM, photos below) other than letting them grow out?

Long version…
I mostly keep my birds for household egg production, and this year was hoping to turn 3 laying Australorps into several more. I planned to hatch a surplus, sell half the chicks in the first week (selecting for friendliness) and whatever cockerels I was left with as soon as I could pick them out. By way of chicken math I also have a small bantam flock, mostly as pets.

“Surely,” thought I, who until now has only ever had standard birds, “that genetic grab-bag of a bantam rooster won’t have the determination to successfully breed hens three times his size.”

I hatch out a dozen good healthy chicks, all of which look perfect at first glance. “But hang on a second!” I cry as I’m putting them in the brooder. “Some of these are pretty small, and two of them have downy legs!” I go out to check the chicks I caved in and let the broody bird hatch—bantams all, and two with feathered legs.

Seems I was wrong about that 4-piece Chicken McReprobate.

So my question is, after having fiddled with kippenjungle’s genetics calculator to no satisfaction, is there ANY way to tell the purebred birds from the less-obvious crosses at this age (3 weeks)? Or am I on the hook to put months of time, space, and feed into a dozen birds before I can be sure?

On the genetics of the adult ‘lorps: I got the eggs from a local small farmer rather than a hatchery, but have no reason to doubt they’re anything but Australorps—heavy-bodied, clean-legged, soft-feathered birds in blue, black, and splash, laying brown and tinted eggs. Not show quality but definitely of the breed. (The roo’s comb was more impressive, but we had frostbite issues last winter).

On the genetics of the white bantam: Absolute mongrel. I cannot speak to the genetics going on here, except that he is clean-legged and must have something masking a mild feathered-leg trait. I got him an a batch of random chicks from a fellow who has mixed flocks that free-range and breed at will, and only kept him because my MIL liked him. He has a date with the slow cooker if the guy won’t take him back.

On the appearance of the chicks: I know some white feathering is normal on black chicks, but I feel it’s more extensive on a few of these than when I raised their parents—is this a tell? I banded the ones (amber bands, blue bands are for the friendliest ones) that were clearly smaller at hatch just to keep tabs on them, but I'm seeing less difference at the 3 week mark.
IMG_4261.jpg IMG_4284.jpg IMG_4659.jpg
Any help appreciated!
 
I'd pick the larger chicks you like best and sell the rest, regardless of other qualities.

I don't see any way to safely tell the parentage of these, especially since you have a blue and a splash hen in the mix. There may be hidden color genetics in any of them, and it's possible the feathered legs come from one of the hens and not the rooster. Just no way of knowing.

Unfortunately in this case, Australorps have the dominant traits of white skin and black or black dilute coloring. Comb type isn't a factor here, either.
 

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