I overheard a couple of photographers talking in the parking lot of a State Park. They both brought their "big Tamrons", but opted to leave it in the car instead of bringing it along. They went on to justify the decision with, "If I need it, I'll mozy on back".
This is a problem for several reasons.
1) To prevent theft, long lenses and expensive camera gear should NEVER be left in your car, VW Bus, Hybrid, etc.
2) The need for a super telephoto lens does not announce itself, it just happens! A bird could land nearby, a bear may appear in the distance, etc. These animals don't usually hang around, so you need to be ready. By time you "mozy on back" with your Bigma lens, your subject will likely be long gone.
3) If you can't carry it, what's the point of having the lens at all? Telephoto lenses are awesome tools, but you should be able to hike with it. Instead of a hefty 500mm f4, consider these 400mm prime and zoom options. They are all very sharp and powerful without weighing a ton. In addition, they'll fit in a photo backpack so you can stroll deep into the woods, well off the beaten path.
Later that same morning, this Red-tailed Hawk landed a few hundred feet away from me. I used the Canon 400mm to photograph it with the flowering trees in the distance. It was a glorious sign that Spring truly has arrived here in New York. While I never did see those two photographers again, I hope they're story will prevent others from making the same mistake.