MrBumps2U,
The lens I used is Nikon's 200 - 500. It is new to me as about 3 weeks ago! Previously I used Tamron 150-600. I think the plan would be to bring the longest lens you have and a tripod. Also a wide angle will be nice for the scenic shots. The main gear I'd encourage is the warmest set of long johns to parka that you have. It always seems much much colder than the numbers read. Probably because much of the time you'll be just standing and the only movement producing heat is your shutter finger. I envy you learning on such a group setting. You'll jump a couple years experience on your first run. Usually people arrive before it begins to get light, and set up by a pond where it has been determined the cranes and geese are roosting overnight. As soon as it begins to get light, you will see the birds and people will begin blazing away. Fact of the matter is - most folks will rip off several hundred before sun up. When the sun hits the water, all previous images will be dumped! You may see cranes or geese coming in, or just the departure of those roosting. The cranes will usually go first and begin taking off in ones, twos and small groups. It is very considerate of them. You will quickly read that those intending to take off will lean into the wind then start their run for take off into the wind. Most of the time there will be an hour long repeat until there is not one single one left. Somewhere in there, perhaps first, perhaps not, the snow geese will explode into the famous fly out. In the old days, when they roosted in a different spot, the numbers were larger, but it is still spectacular. Many times I forget the camera and just stand in awe... If conscious you just aim into the mass of birds and hold the shudder down and hope for the best, and hope no poop hits your lens...it happens. Then there is glorious silence and a line up of a hundred or so photographers stand around grinning and looking silly at each other. Pretty spectacular! With luck, the snows may circle around after awhile and land again and repeat... Then, when the ponds empty, you'll likely get into vehicles and start driving the loop. That's a slow crawl around a several mile figure 8 with many turnouts. The critters will be on the road or nearby and more birds on various flooded places, and probably massive numbers in the fields. It is rather comical to see a string of cars slowly going along, then a dozen folks spilling out with half a million bucks of gear in hand! I hope you have fun! It is really a very special place! If you want, take a look at my site https://ralphlind.smugmug.com/Nature It's not well organized, and probably best to start with the most recent galleries which will be at the bottom of the page.
Wishing you will!
Ralph