When I ran canoe expeditions I had a 70-210 mm lens that I used on the water, and a 28 to 85 mm lens that I used most of the time in camp. The key was to have some overlap in the ranges. I think the optimum overlap is about 25-30% of either the shorter end of the longer range lens or vice versa. Right now I have a 10-24mm lens and a 18 to 140mm. The overlap reduces the number of lens swaps by about 3/4
More recently I have done trips with only an 18-200 lens on the camera. This is a winning combination, as the lens and my D7100 is moderately weather resistant. Having this around your neck all day on a hiking trip can be wearing. I have a case that fits the camera with this lens on, and modified a computer bag strap sewing a 4 layer fleece tube on the wide, but abrasive nylon.
When I was shooting canoe trips, I sold complete sets of pix. At that point I could get them printed dirt cheap if I did it at the time of developing. (It was interesting to see the look on clerk's face when I dropped 8 rolls of 36 on the counter and asked for 35 prints of every frame.) But this meant there was NO post production editing. Exposure had to be right, and cropping had to be right in the camera. It was much like shooting slides. Using zooms allowed me to fill the frame with a canoe and white water from the shore, and to get candids in camp without getting in their face.
My wife has a 35 mm f/1.8 prime, which I have borrowed, and I have a tamron 90 mm macro that I use for plant closeups. I keep catching myself trying to zoom, instead of walking forward or back. Drives me crazy.
Anyway, in your shoes I would sell both lenses. Get the 18-140 zoom, which is one of the best kit lenses out there, And pair it with the 70-300 zoom which is much lighter than any of the 50-300's that nikon has made according to this chart: http://www.photosynthesis.co.nz/nikon/specs.html
100-300 would be a better fit by my overlap rule. It doesn't look like 100-300mm is a common size. Nikon used to make one, but it's no longer in production, but you can find it on ebay for about $200. Manual focus lens. Sigma has one at f/4, also discontinued,but readily available. Sigma also has a 120-300mm at f/2.8
If you are deeply into wildlife, then consider a set with 10-24, 18-200, and the Tamron G2 150-600. This gives you reasonable overlaps.