I had a thought earlier today. If I manage to hatch Icelandics but not any Tomarus, so that got me thinking big time. I came up to this reason, and you guys can shoot it down if I am wrong.
My reasoning-
Icelandic chickens- Country of origin- Iceland
The country of Iceland is very far north with limited amount of daylight, and cold most of the year.
The Icelanders must have bred/selected, or even the birds themselves produced roosters that can be fertile year around in order for the breed to survive in a tough country. And egg production was a must. They were used as a necessary livestock.
Tomaru Longcrowers- Country of origin- Japan
The country of Japan is further south and has more daylight and warmer.
Longcrowers is an ornamental breed, so they were bred for longcrowing, and egg production was not valued as much as the crowing, but still important. They are just for looks or rather for hearing.
Was not used as necessary livestock.
Quite a different between the two breeds, huh?