Because I keep many birds, I've read many books on the topic by Matthew Vriends. Vriends raises several kinds of tropical birds, visits their natural habitats, is involved in the preservation of wild birds and their habitats, and writes extensively on these topics. He is also a PhD (Dutch born biologist and ornithologist). I bought THE PARROTLET HANDBOOK in spite of the fact one reviewer said there was not much of interest about Parrotlets in this book, mainly because I have read so many of Vriends other books on other birds and found them helpful.
THE PARROTLET BOOK is very interesting, but it is also geared to the breeder of this type of bird. As the owner of two brother Parrotlets, I don't foresee joining the breeder group any time soon, even though Vriends makes a compelling case for becoming a breeder of Parrotlets who are under threat from the deforestation of the Amazon jungle.
In spite of the book's bias - which I truly appreciate, it does include many helpful tips and a good deal of information about the various types of Parrotlets who are companions of people like me. For one thing the book helps one understand the origins the little birds whose ancestors come from South America and who seem be thought of by some as the little brother of the larger Macaw.
My Parrotlet brothers have been hand raised from the egg stage and they are Soooo sweet. However, I am told the Parrotlet can administer a nasty bite should he be "wild" or displeased. My birds perch on my finger (two at a time) and are a lot less messy than my Cockatiels and Love Birds. Maintenance-wise, keeping Parrotlets is a bit like keeping Canaries. However, they are as playful as my Senegal parrot.
I found a really great article on Parrotlets entitled "True Confession-Parrotlet owners bring down the house with tales of pin-sized adventures" in the January 2004 issue of Bird Talk Magazine (if you keep birds or are thinking of doing so, subscribe to this magazine). I recommend both Vriends book and Bird-Talk magazine for the serious bird owner.