Hmm. It's not often I disagree with SuKi, but here, since you have a sentence related to behavioral science, I think "behaviors" is quite common. The subject exhibited many different behaviors: yelling, jumping up and down, etc. The different "behaviors" relate to different types of "behavior": physical, verbal, emotional, etc. So, in your sentence, the correct word may well be "behaviors".

Normally 'behavior' / 'behaviour' is an uncountable noun with no plural form. Occasionally you come across a very specific use of the word in the plural form in some academic fields such as psychology. In most other cases, it"s best to use it as an uncountable noun. In your example, the singular form is fine.

Yes, but I think the meaning is slightly different when using "behavior" as an uncountable mass noun and using it in the plural. For example, I feel sure that "behaviors" is correct in this sentence: "Potato washing in macaques, and milk bottle opening in British birds, are two behaviors for which there is strong evidence of cultural transmission."