I was going to say that as you mentioned working in the field that a good compact camera or phone would likely cover you for darted animals since you'd be working and, in my experience, a big camera just gets in the way or ends up sitting in the bag the whole time when you're focused on work (esp in something time sensitive like that where you've a limited window to perform all your tasks within). Though sometimes experience and a larger team can give you time to shoot, even if its just documenting the surveying method and the animal and any notable features worth keeping an eye on. Otherwise you've had solid advice already with working within your budget. Canon or Nikon would suit you well, though Nikon has the lions share in terms of backlog of second hand lenses to choose from at cheaper prices provided you don't mind manual focusing on some. Both have the same range of modern 3rd party lenses to pick from. That said at present Nikon is ahead in sensor technology (broadly speaking). So the current trend is toward them.