A plump of moorhens
Like the community answer, it is correct that moorhen is the name of the species and not the gender. Within moorhens, there are cocks and hens like with other bird species, but moorhen is the name of the species itself.So the male here would be called a moorhen cock (or cockerel).
wwaqawqa
Because they are water birds.
owls and other dusky moorhens
Marion Petrie has written: 'Winter flocking in moorhens'
A group of Dolphins are called a Pod
A group of dolphins is called a pod. If that is your question.
A group of hens is called a brood.
a group of Blackbirds is called a murder
A group of martens is called a "richness."
A group of grouse is called a "pack".