He knew that there would be no time nor library references in Africa, and so he had prepared them in Washington before leaving America.
In regard to his future movements he seemed sorry that he was obliged to take the Nile trip, and that he was only doing it as a matter of business--that he had to get a white rhino, which is found only along certain parts of the Nile.
"Going back by the Nile is a long and hard trip.

For the first twelve days we will not fire a shot, probably.

It will mean getting started every morning at three o'clock, marching until ten, then sweating under mosquito bars during the heat of the day, with spirillum ticks, sleeping-sickness flies, and all sorts of pests to bother one; then long days on the Nile, with nothing to see but papyrus reeds on each side." And speaking of "rhinos" suggests a little incident that the colonel told and which he considers amusing.
"One day one of the party was stalking a buffalo, when a rhino suddenly appeared some distance away and threatened to charge or do something that would alarm the buffalo and scare it away.

So they told me to hurry down and shoo the rhino off while they finished their stalk and got the buffalo.

So, you see, there's an occupation.