First off, I was replying to CHARLESTON 1979 and trying to help him with my opinions. I've never seen, or don't really remember seeing any of your images or examined any of the EXIF data of your images so I can't really comment on which ones are or are NOT keepers. Using a 1/10 shutter is extremely difficult to do at the long zooms such at 400mm and up. I don't know what your focal length was for your Night Heron or how the lighting conditions were. If you were happy with that image, and you used a 1/10 shutter then that's great. I've got some shot at 1/6 shutter that I've kept. But if you read what I was saying, I said "most" are not keepers at such slow shutters. I didn't say all. When I have really low lighting conditions like I've talked about, I try to steady my camera on something, and use burst mode. Maybe one in 20 will be sharp. Or I use a tripod. But hand held will not be very easy to get ANY keepers. Although, you can get lucky and get some that are. It also depends on your experience, skill and technique. Not likely that a beginner that is asking this question that the OP is asking is going to net great results for some time using a really slow shutter speed like 1/10th.

To answer your question about flash at 1/200 or 1/250th (sync speed of Nikon and most other cameras for that matter) will NOT give you a double exposure. You should give it a try. I'm not saying that using flash on birds in low light conditions is the best thing to do under all circumstances, it's just another tool you can try. I've used it many times, and try to avoid it unless I just can't get anything else to work. I recently used a flash on a hummingbird nest and each time the mother hummer came back to feed the babies I used flash because the nest was under the canopy of a large tree with no direct sun on the nest. It was in the darkness of the tree shade and the tree was large that ambient light was very low. I did try ISO 3200 and a shutter of 1/200th but that was not cutting it. So I put my flash on the hot shoe and the flash was freezing the wings for the most part. I'll see if I can find some of those images now and post one here.

As I said, flash isn't always the answer. Experience, technique, and skill attained over a period of time is the answer. Knowing what will and what doesn't work is always helpful. Some people I know use shutter priority most of the time. I'm not a fan of that so I use aperture priority most of the time except when using flash. One other thing about flash is that some birds eyes are greatly affected by the flash. Owls especially. I think Night Herons might also have the kind of eyes that will not tolerate flash well. Flash does weird things to the eyes. Also, flash can make some images appear very flat. Sometimes with a little post processing you can bring back some of the contrast to undo what the flash does to make them appear flat.