Scientists say a newly developed family tree for hummingbirds shows the tiny creatures originated in Europe but the evolution of the bird's many species exploded when they arrived in South America.

From Europe they spread through Asia and North America, but found an evolutionary "Garden of Eden" when they moved into South America around 20 million years ago, researchers at the University of California, Berkeley, say.

"Our study provides a much clearer picture regarding how and when hummingbirds came to be distributed where they are today," study lead author and integrative biology Professor Jimmy McGuire says.

Once they arrived in South America, hummingbirds quickly spread across the continent, evolving the many sizes, shapes and dazzling iridescent colors seen today, he says.

That diversification led to around 140 new hummingbird species, and new species are still evolving.

"We are not close to being at the maximum number of hummingbird species," McGuire says. "If humans weren't around, they would just continue on their merry way, evolving new species over time."

The evolutionary branch that leads to today's hummingbirds started around 42 million years ago, splitting off from a similar group of birds, the treeswifts and swifts.

The split likely occurred in Europe or Asia, before hummingbirds spread to South America, most probably by way of Asia and across the land bridge connecting Siberia with Alaska and then south.

Upon reaching South America they experienced an evolutionary explosion, the researchers say, into nine distinct types known as brilliants, topazes, mountain gems, hermits, bees, mangoes, coquettes and a single group containing just Patagona gigas, the Giant Hummingbird.

Genetic analysis confirms hummingbird diversity is still rising today, as new species are evolving at a faster pace than extinction rates, McGuire says.

"When it comes to vertebrate animals, hummingbirds are about as diverse as they come," he says.

One puzzle still unsolved is how hummingbirds managed to achieve a toehold in South America since they are dependent on plants that evolved along with them to offer unique feeding adaptations.

"It is really difficult to imagine how it started, since hummingbirds are involved in this coevolutionary process with plants that has led to specializations we typically associate with hummingbird plants, such as tubular, often red flowers, with dilute nectar," McGuire says. "They drive the evolution of their own ecosystem."