This question received some downvotes and has a negative score. How can I improve this?
You asked a question that would have been easy to find after a cursory internet search. To some people your question shows a lack of research effort and implies you are attempting to push the question towards a particular answer. If you know one date, you do not explain why you could not find the other birthdates, or at least what is preventing you from doing your own research to find them.
To some users it may seem like you are ask a question for the sake of asking a question, instead of asking a question because because you have an legitimate problem you are unable to figure out yourself.
If an answer is easily searchable with a cursory internet search, it is regarded as an "low-effort" question and maybe put off users from answering, because you could have done it yourself if you made the effort.