Charlie, a lot of lenses can do the job. What matters is your technique, patience and the birds' acceptance of your presence. If you are not using cabled remote and focus trap it requires a bit more patience. I cheaper/slower lens can do the job, but it's harder to focus quickly in dimmer light. I have included a link to the EXIF below each image.
Sample DA 50-200 "kit lens" shot, at only 1/125 sec.:
EXIF
Now with a much more expensive lens - the FA* 300/2.8 @ 1/500 sec.:
EXIF
The above images are a personal preference I have to photograph hummers: tack sharp on the eye, but motion blur on the wing to demonstrate activity/motion in the subject. I also posted 4 images in 2 posts on how to shoot hummingbirds in low light and a low shutter speed. I would encourage you to look at the images to see "how low can you go" with successful results...
https://www.pentaxforums.com/forums/post-your-photos/58528-reflections-their-...rd-images.html https://www.pentaxforums.com/forums/post-your-photos/58779-more-reflections-s...s-part-ii.html
In the above posts, long lens technique is critical. I'd be more than happy to cover some of it if needed. However, I am using a much, much heavier lens than you are considering - it's 5.5 pounds, just for the lens! you can do a good job with your choices, but knowing your lighting options (how bright is it when you can photograph, etc.). I have to contend with trees filtering the light if I shoot at the end of the day.
Regards,
Marc