I work in the tourist industry, on a cruise ship. I never expect tips, though I do appreciate them. Tips help me in more than just monetary ways, they help me emotionally and mentally. They feel like a thank you that is more than just a handshake (though those are appreciated too). It gives me a sense that my extra efforts, (which are unpaid and start months before the season), are recognized and appreciated. But mostly, tips help raise my spirits and keep my energy up. It is really easy to get burnt out, particularly when you have a job that requires travel and many new faces. Yes I am American, but I don't count on tipping for income, infact the company I work for does not require it. That said, I will always tip for good service (sliding scale), it is a gift that is both immediate, and carries on to the next guest.
I do have a non-monetary tipping idea... In many countries bird books are difficult to come by, or are cost prohibitive. I often carry extra bird books to give away. They are perfect to give to guides, schools, lodges, and other bird nerds. Giving them away makes room for return gifts or souvenirs, and lightens my load. Even older books are appreciated. I took a couple copies of Songbirds of South America (Ridgely and Tudor 2009) with me to Columbia and they went over great, in some cases, better than money. It is a gift that gets passed on from current to future generations of bird guides and from which their guests also benefit. With luck it will encourage some young person to become a local bird advocate.
Happy birding all!