Does observational data need further proof? Within fields like animal behavior, data is often collected through observation of the subjects, either in the wild or captivity. 


Can a paper be published purely based on observational data, with no evidence in video or audio to support it? 
If so, could one (in theory) generate an entirely fictional dataset of observations as basis for a publication? Or do other mechanisms exist to prevent this kind of fraude from happening?
Are there examples of publications, in animal behavior or other fields, being exposed for generating completely fictional datasets? If so, which?
In many experimental fields, it is possible to "generate" a plausible amount of data and get away with it (i.e. publish the data and the conclusions in a peer reviewed journal).

Experiments need to be repeated independently. Otherwise, all sorts of things happen. Real fraud is probably the lowest number. Much more important are cases in which experiments are done without enough care or statistical methods are used in a questionable way.