I have led a number of walks in my time and the question I get asked most is than 'What was that?' and it is usually followed by 'How do you know?'. New people to nature watching often place their entire emphasis on plumage colouring and forget all the other factors. For example, we handed over our RSPB credit card with a picture of a kingfisher on it in a local shop recently and the shop assistant said 'My wife saw a kingfisher in our garden recently'. I asked him whether they lived by a river or the coast and the answer was 'No, near Wareham Forest.' I suggested it was a nuthatch rather than a kingfisher and the response was 'How do you know?'
This is obviously a picture of a kestrel, but how do you know? Chestnut brown colouring; mottled plumage underneath; black bars in the tail; but there is something far more obvious, what is it doing? It is hovering; it is hunting; therefore it is a bird of prey and, as the only one that hovers is a kestrel then you do not even need to lift your binoculars to see the plumage markings (by the way buzzards do hover of sorts too).
It is not just about plumage it is about size, shape, posture, movement, activity, location, time of year, time of day, population numbers, instinct, experience, a whole bundle of things. This is not just true for birds but for every facet of wildlife, including flowers and other plants.