In life, bigger is usually better, and the same typically applies to the animal kingdom as well. But a new study has found that occasionally, just like when David beat Goliath, small species of birds can dominate larger species during aggressive interactions, especially when they spar with distantly related species.

Body size has long been recognized as a key ingredient in shaping species interactions, with larger species usually winning conflicts with their smaller counterparts. But Queen's University biologist Paul Martin, who published his findings in the journal PLOS ONE, provides evidence that though a species may be small, the evolution of certain traits can allow them to overcome their disadvantage in size and prove that sometimes brain is better than brawn.

"The 'larger animal wins' rule that usually governs species interactions, and often influences where smaller species can live, is more likely to break down when the interacting species are distantly related," Martin explained in a statement.

"We want to understand why species live where they do, and how different species partition resources, like food, in nature," he added. "This research feeds into that."

In the study, Martin observed the outcome of 23,362 aggressive interactions among 246 bird species pairs, including vultures at carcasses, hummingbirds at nectar sources, and antbirds and woodcreepers at army ant swarms.

It turns out that the advantage of being large in size diminished as the evolutionary distance between the combating species enlarged - a pattern explained by the evolution of certain traits in smaller birds that enhanced their abilities in aggressive contests. Specific traits that make smaller birds ones to be reckoned with include well-developed leg muscles and talons, quick speed, flight acceleration and maneuverability, as well as traits associated with aggression such as testosterone and muscle development.

Unfortunately for some size-challenged species, this kind of advantageous evolution is not displayed.

"We really want to understand why some species can overcome the disadvantages of small size, while other species cannot," Martin said.