Looking at the standard definitions of instinct reveals a deep conceptual confusion. Here is a simple example.
"An instinct is something you don't need to learn; it happens naturally, without you even thinking about it."
This definition is a good example of the mistaken idea that instinctive behavior does not require thinking. The many cases discussed here at Horse Cognition show that complex instinctive behaviors require a lot of decision making and that means thinking.
A complex instinct is a body of expert knowledge that is not learned. Nest building by birds, dam building by beavers and grazing by horses are examples of complex instinctive behaviors.
Part of the confusion is that there are also simple instinctive behaviors, which do not involve thinking. Fear of snakes may be an example.
Many definitions also include the notion of environmental stimulus. I imagine this stimulus-response model is the influence of behaviorism. But while the arrival of spring may stimulate a pair of phoebes to build a nest, it does not tell them where to build it, nor which specific materials to use, nor how to find them. These are all complex expert decision making processes. If anyone doubts this I invite them to try to build a nest.