From the sentence we can conclude that the subjects saw different 'breeds' or 'variants' of birds. Thus, the answer must have meaning close to these words.
Option A is incorrect. Although, types can mean 'variants', it is usually used to refer to variants of non living things and not birds. Thus, it is not the best fit.
Option B is incorrect. Branches means 'divisions'. It does not have the required meaning. Thus, it does not fit in the blank.
Option C is correct. Species means 'breeds'. It is generally used to refer to variants of birds and animals. Thus, it is the perfect fit.
Option D is incorrect. Kinds also means 'variants'. It fits in the blank but 'species' is a better fit because it is specifically used for birds and animals.