Sex link

Sex-links are cross-bred chickens whose color at hatching is differentiated by sex, thus making chick sexing an easier process. Sex-links come in several varieties. As hybrids of laying or dual-purpose breeds infused with extra vigor via heterosis, sex-links can be extremely good egg-layers which often produce 300 eggs a year or more depending on the quality of care and feed. The color of their eggs vary according to the mix of breeds, and blue-green eggs are possible.

Many common varieties are known as the black sex-link (also called Black Stars) and the red sex-link (also called Red Stars). More specific variety names are common as well. Black rocks are a cross between unique specially bred hybrid strains of Rhode Island Red rooster and a Barred Rock hen. Red sex-links are a cross between a Rhode Island Red or New Hampshire rooster and a White Rock (This variety pair is known as a Golden Comet), Silver Laced Wyandotte, Rhode Island White or Delaware hen. One example of a red linked breed is the Red Shaver. Europe has the Cream Legbar (an actual true-breeding pure breed) in Spain this variety is "soniquetera"and ISA Brown sex-links, which also are found in Canada.

Chicks of a single breed that are similarly sex-linked are called autosex chickens, a term developed to differentiate between sex-linkage in purebred chickens versus sex-linkage in hybrids.

A Red Sexlink rooster "Freckles"

A Black Rock hen

A red sex-link pullet

A black sex-link rooster "Harry"

Shipped pullets

Red sex-link hen "Linda Lee"

Black Sex-Link rooster

...
Wikipedia