Luck roll: (DM rolls 1d20: 15!) There's a war banner above the desk. You snip a string and it flutters down over the cage. Bird Int check: (DM rolls 1d20: 6!) The bird's squawks of "Hey! Maid! Come back and clear this away!" are nearly inaudible. The papers, bookshelf, desk, and wooden chests are at your disposal.
First a quick scan through the papers and over the desk - anything unusual?
1 plus bookself. Search any desk drawers , and examine the chests without opening them yet.
You step out, cast Invisibility, and step back in. The bird (which seems to be made of glass) ignores you. Without moving any papers around, you can see that the top sheet is a scrawled troop list. It adds up to 400 infantry and 200 cavalry in various places in Arthana; 80 elves; 200 infantry and 7 ships from the Sea Cities; and, in different ink, "Hartwin and 5 golems."
Cast magic missile on the bird. It's made of glass, so it can't be too tough.
Is there a way to let something like a tapestry fall on the cage to cover it?
Make notes of all of the troop numbers and locations and keep searching without disturbing anything.