For the cowbird this is normal. Cowbirds are brood parasites, it’s snuck in whilst the robin was away and laid it’s egg for the robin to raise. If the robin is smart enough to notice what’s happened they will often still raise it anyway, as the adult cowbird will be keeping an eye on the host nest and will destroy the other eggs if the robin rejects it.

If you’re doing a holiday in the USA and renting a car via enterprise, Alamo or national book with Rentalcars.com, unless you’re flying with doing a Virgin package holiday, in Which case do it with them. They have the best rates in the market due to special agreements. If you want the best customer service experience for rental cars book with Virgin as they will put a lot of pressure on Alamo/national/enterprise who will bend over backwards for you.