Gene51 wrote:
When I am birding I am walking around, and my walk around lens is a Sigma Sport 150-600 - but I wouldn't mind losing 2 lbs and getting a Tamron G2 - Walk around lens is a silly concept. You take the lens you think you will need to get the job done, or if you have no clue what you are going to encounter, then bring a walk around camera - like a bridge camera. I'd rather use a bridge with a good lens than a dslr or mirrorless with an average lens.
To me, a walk around lens is what I use on a casual stroll if I am not particularly interested in longer shots, but rather anything opportunistic that strikes my fancy. A 35 or 24-70 is usually my choice, but some, like my wife, prefer a more versatile 18-140 to 18-400...relatively light weight and covers most anything of interest. If I wish to be prepared more for birds, depending on the cover I will carry a 70-200, 200-500 or 150-600 G2 if light is decent. I use a shoulder strap attached to the lens foot or L-bracket for smaller lenses and have the length adjusted so my hand guides or holds my set up near my hip. It is comfortable and the bigger lenses are not a big chore. I use an arca-swiss quick release clamp and deployment to a mono, tripod or body-pod is quick and easy. I have thought about the bridge camera scenario you mention and its many advantages, but I'm too used to my dslrs and my simple mind would have difficulty with the transition!