Two birds that look very similar to each other have always been considered two distinct species based on differences in their body size and in where they live. a group of ornithologists studying the two species begins to think they might not be separate species based on observed behavior. what would be the best next step regarding this new hypothesis?

run dna tests on the two species to see how genetically similar they are.
publish their conclusions in a scientific journal to officially change their classification.
trace the birds' ancestry in the fossil record to see if they diverged into two species.
compare embryos of the two birds to see if they differ during development.