All I can say is that it happens to every birder and sometimes the difference is sooooo obvious, I want to smack myself in the head. But I am in good company. We joke at Wild Bird Rescue about our shapeshifting birds on occasion. Sometimes a bird comes in and during intake we identify it as one bird. Later you walk by the cage and it's like you're looking at an entirely new bird, and we end up changing the ID. Of course babies are harder to identify--they sometimes change into a different bird as they grow up and more adult features show up. There just isn't much in the way of baby bird ID guides out there. But that's more understandable than some of the blatant field errors.
Why do we make mistakes? It could be a number of reasons.
- Some birds just look a lot alike. Telling a western meadowlark from an eastern is iffy business if the bird is not singing.
- Sometimes there just isn't a lot of time to make the identification. Trying to identify a sparrow in the nanosecond you see it go from one place to another is a challenge.
- The lighting could be bad and you cannot see colors or identifying marks.
- No bird looks exactly like the field guide shows. That's why many show different views of the bird and most birders have more than one field guide--they all show the bird a little differently.
- Sometimes you "want" a bird and can pick out the field marks you want to see and not see the rest.
- Plumages change throughout the year and sometimes from one year to another.
- Some species have a lot of variation. Red-tailed hawks for example are notorious for the variation in their plumages.
- We're human. We just get it wrong.
So I confess to being human, but I don't have to like it.