Grazie Marziotta, it is pretty clear to me now, gatte is pronounced more lightly than gatti, as if it was gatteh, while gatti I have to emphasize on the ending like gatty, again thanks a lot and have a wonderful day :-)
Not quite. L'acqua can mean 'water' in general (as it has been used reguarly up to this point in the Italian lessons) whereas 'acqua' alone means an unspecified amount of water. Both can be translated simply to 'water' in English.
A dictionary is useful for finding out if there is a féminine form. According to mine, there is no feminine form of "uccello". Other animals do have a féminine form but if you don't know the sex of a particular animal(s) it is more normal to use the masculine form.
Because the sentence starts "le gatte". If the speaker did not know the gender of the cats he/she would most probably use the masculine plural, "i gatti". Female plural is normally only used if you know they are all female.
Referring to a known female cat in the masculine form is generally because the person thinks of the animal as an object, a bit like saying "it" for the family cat in English. Someone who cares for an animal will refer to it in the correct form.
From what I understand if the sex of a group of cats is unknown or mixed, it would be I gatti and masculine is predominately used if in doubt. Cats and dogs can be referred to as masculine or feminine. In this case they are female.