How does a bird know how to build its nest, without being shown by another bird?
Hard-wired, I guess. Kind of like walking vs talking. If a human was brought up by animals, it would automatically start walking, even if looked after by quadrapeds. However it wouldn't suddenly start rabbiting away in any language unless it had been taught.
Humans are incredible learners, which makes us very adaptable and puts us at the top of the food chain and resident in almost any part of the world. Hard-wiring makes an animal appear to be much more capable, but not adaptable. In the absence of twigs and moss, I guess most birds wouldn't be able to bring up youngsters.