To get more sourced material acceptable to the mods, you will probably need to narrow your question down to WHICH birds you were interested in (there are very few papers published that just talk about generic “birds”!) but the short answer is: a lot of bird behavior is a bit of both. They will inherit instinctive behaviors they can perform with no experience when they find themselves in the right conditions to trigger or “release” the behavior, but over their lifetime they will also practice and learn to get better at performing them, or figure out ways to modify them if something about their first instinctive attempts don’t work.

Here is an article that cites sources but is written for a non scientific audience, about one of the coolest examples of this. Different types of lovebirds will carry nesting material (strips of bark and leaves in the wild, often strips of paper in captivity) using different methods: peach-faced lovebirds will tuck multiple strips into their feathers and carry them that way, while Fischer’s lovebirds will carry one strip at a time in their beak. These species can also be hybridized. What method do the babies use?

> Dilger found that the hybrid lovebirds demonstrated a confused combination of the two nest material carrying strategies: initially, the young birds tucked the nest material (strips that they had chewed from a larger piece of paper) into their flank and rump feathers but failed to let go, so they pulled them out again and again, repeating this pattern many times. As the birds matured and gained experience over a period of three years, they eventually settled on carrying nest materials in their beaks, like their Fischer's lovebird parent. However, they still maintained a peculiar ritual associated with the tucking of nest materials, like that of their peach-faced lovebird parent, prior to flying off with the paper in their beaks.

It must have been so frustrating for them to have an urge to tuck those strips in but not be able to get it to work right!

If you’re interested in other instinctive bird behavior, look up “Fixed Action Patterns.” We are starting to learn they’re not always quite as “fixed” as they used to believe, but it’s still incredible how many surprisingly complex behaviors can be inherited and performed without any trial and error learning beforehand. Hope this somewhat answers your question!

Edit to add the link I forgot: https://scienceblogs.com/grrlscientist/2007/12/06/lovebird-behavior-nature-or-nu