A naturalist's insights on birds - and life; Nature Through Tropical Windows, by Alexander F. Skutch. Illustrations by Dana Gardner. Berkeley: University of California Press. 374 pp. $19.95.

In these days of strife in Central America imagine finding wrens nesting in a bunch of bananas and immature birds helping their parents raise younger broods! ''Nature Through Tropical Windows'' is chock full of wonderful discoveries, related in a lucid style with a slight period flavor.

For over 50 years Alexander Skutch has been studying plants and animals in Central America, mainly Costa Rica, and reporting his findings. His latest book continues the pattern of ''A Naturalist on a Tropical Farm,'' alternating accounts culled from his observational notebooks and journals with reflections arising from them.

The chapters on bird behavior will tell some readers perhaps more than they ever wanted to know, but if they at least skim this information they will be able to better appreciate what Skutch has to say in the rest of the book. The author is a meticulous scientist who has made a big contribution to ornithology, filling in large gaps of knowledge about birds in the tropics.

Over the long haul, Skutch has seen enough evidence of harmony and cooperation in nature to make him wish to counteract the current fascination with violence, aggression, and disaster in the world. He has done so to a remarkable degree in his own life, which adds to the authority of his philosophical essays. He is also honest about inevitable ethical dilemmas.

In the preface he comments, ''Through intimate association with the living things around us, we reach out beyond the narrow human sphere into the larger natural world that surrounds and sustains us.'' He notes that we develop an attitude that may grow strong enough to influence our conduct. ''Perhaps to have developed such a comprehensive outlook, especially if it be hopeful and sustaining rather than gloomy or despairing, is the most important outcome of long association with nature.''

In the last chapter, ''Windows of the Mind,'' Skutch explores the limitations of the physical senses and resultant opacity of the mind and then wonders about what he calls the psychic aspect of being. He speaks of the need for cherishing ''whatever embellishes or elevates our lives . . . to fulfill the cosmic striving to make existence ever more precious and desirable.'' We must keep the windows of the spirit open, he says, and do our utmost to help others do the same.