This is an Isa Brown.
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Not only is the bird in question a cockerel, but the other birds are not ISA browns. They are all either production reds or hatchery RIR. ISA browns would be more orangey brown with white underneath... do a search for photos of Red Sex Links which is a generic term for ISA Brown or any of the other "brand" names and hopefully you will be able to see the difference.
The birds in the photo are red with dark undertones suggesting probably RIR.