In Longman's advanced grammar book the rule says 'The form of the present simple verb only changes after he, she or it, when we add -s to the base form (-es after o, s, sh, ch and x; -ies when the base form ends in -y)
In an example : A colony of Antarctic penguins lives in Marwell Zoo.
My understanding : add 's' only if he, she or it is present
My question: is 'A colony of Antarctic penguins' considered as 'it'? Or am i missing something else?
Yes, "A colony of Antarctic penguins" is considered as "it". Indeed, the subject of this sentence is "A colony". The penguins just represent the composition of the colony. You could replace the sentence by "A colony lives in the city." Therefore, the subject is singular and at the 3rd person. You have to use the -s rule.
So you would write:
A colony of Arctic penguins lives in the city.
Or if the penguins were the subject, you would write:
Some Arctic penguins live in the city.
