Jack Kearney's, "Tracking: A Blueprint for Learning How", 1978, 150 pages. Very plainly written and quick to the point. Border Patrol man-tracking oriented but with clear photographs about tracks and signs applicable to animals.

This ultra-straightforward books covers many bases: awareness, sun angle, sign, slope and ground cover, aging, signcutting, track identification and description, and following non-visible trails, among others. Tracking gear is also discussed.

This book is on my short list. Highly recommended.