Greer Loc: SOUTH GEORGIA

Suggestions please?

Architect1776 Loc: In my mind

Budget?
Start with the Nikon 80-400, 200-500 or the Tamron 150-600 G2.
These are generally in most peoples budgets if somewhat serious about photography and they can put some aside monthly to get the lenses.

Retired CPO Loc: Travel full time in an RV

Nikon 200-500mm. I had a Tamron, replaced it with the Nikon and never looked back.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Budget is important.

This may help, though it is a little dated and does not include the Tamron 150-600 G2, which is a very sharp and crisp.

https://photographylife.com/reviews/nikon-200-500mm-f5-6e-vr

The 200-500 is an ok choice but the Sigma Sport and Tamron G2 are visibly sharper. Before I became aware of this review in 2016, I borrowed the 80-400, 200-500, and all three available 150-600s (not the G2) and pretty much came to the same conclusions as the review.

If looking at build and image quality and you aren't a strict Nikon adherent, the G2 and Sport provide longer "reach" excellent image quality (my basis for comparison is my 600mmF4) and good to excellent build quality. For me, the 200-500 came very close, and if I needed to use Nikon-only products, I might have made the decision to give up a little image quality (picking nits, actually) focal length, and dust and moisture sealing. But I wanted a lens that was more than a fair-weather lens, and ended up with the Sigma Sport. Had the G2 been available, I most certainly would have purchased it instead - since it provides similar image quality at 600mm, and better image quality at shorter focal lengths, has a greater magnification at minimum focus distance, and the big feature - it is 2 lbs lighter. To me the compromises in the 200-500 were enough to take it off my short list. I used the one I borrowed from Nikon NPS for 2 weeks so I had a good idea of what I could expect from it.

Architect1776 Loc: In my mind

Pistnbroke Loc: UK

Don't even think of the tamron or sigma had both ..junk Get the Nikon 200-500. set the AF fine tune and again after you used it a bit and all will be magic. Grey import at about £800 /$1000 . D750 wrong camera really not enough POI

rstipe Loc: S. Florida

Sigma 150-500 in the for sale section here in UHH.

Pistnbroke Loc: UK

Sigma 150-500 ..old lens forget it get the latest .

ekfelton Loc: Michigan

If you have the budget the Nikon 180 - 400 with built in 1.4 T/C is the one to purchase. It is unbeatable.
Just my 2cents

DavidPine Loc: Fredericksburg, TX

I like the Nikon 200-500 f/5.6 coupled with the D500 (dx). The D750 is a really good camera. I have one and I like it a lot. It isn't the best birding camera like the D500 or D850.

jmw44 Loc: Princeton, NJ USA

The same for me. The 200-500 is heavy, but it's an incredible lens.

rstipe Loc: S. Florida

There's not much to be gained from negative remarks about different brands, unless you've had personal experience with that particular item. I think it's swell that you fancy one specific brand, however the statements concerning Tamron & Sigma are way out of line. Please refrain from trashing other members' comments Or their attempts to sell their items. JMHO

Tommy II Loc: Northern Illinois

I have the Sigma 150-600 Contemporary, and love it. Supposedly the Sport is better, but the weight and extra $$$ we’re not attractive to me. Contemporary was quite enough Lense for me. Takes beautiful pictures, when teamed up with my Nikon D-500. I’m sure it would thrill you when attaching it to your D-750. Try one first if you can.

Tommy II Loc: Northern Illinois

“Junk”? But then again this is from someone who lives on that crappy island.

Pistnbroke Loc: UK

Tested the sigma and struggled with the T 150-600 on and off for 2 years. Maybe it was a bad one but the N200-500 is superb . With all the changes re mirrorless perhaps best to stick to Nikon.

Perhaps tommy your racist comment are not appropriate.

Signed out ..leave the OP to conclude