Most certainly! As a matter of fact, thanks to new scientific techniques we know that the number of animals that ‘cheat’ (have extra sex with other partners) far outweighs those that remain faithful! FUnnily enough one of the last animals we think is monogamous (has one partner only) was the penguin, but new evidence is showing that they too are engaging in extra sexual exploits!
If a female swan does not produce viable eggs the male will leave her and find another mate! While they cheat is not the same as when humans cheat as animals don’t have the same demands made on them to be monogamous so they don’t feel guilty about it and their usual partner won’t leave them over it. So they are a bit more laid back than we are over cheating partners!