How David Beats Goliath: Why Some Tiny Birds Win Out Over Larger Species

When it comes to body size, larger species usually win out over smaller ones. Yet occasionally, there's a case of David beating Goliath. Now one biologist has found that sometimes small species of birds can dominate larger species during aggressive interactions, especially when they interact with distantly related species.

"We want to understand why species live where they do, and how different species partition resources, like food, in nature," said Paul Martin, the lead researcher, in a news release. "This research feeds into that. 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."

In order to get a better view of species interactions, Martin examined the outcome of 23,362 aggressive interactions among 246 bird species pairs. These interactions included vultures at carcasses, hummingbirds at nectar sources and antbirds and woodcreepers at army ant swarms. In particular, Martin looked at the outcome of aggressive contests for food.

In the end, Martin found that the advantages of large size actually declined with increased evolutionary distance between species. This is probably due to the fact that there was evolution of certain traits in smaller birds that enhanced their abilities in aggressive contests, such as well-developed leg musculature and talons, enhanced flight acceleration and maneuverability.

"This study examines broad patterns across many species, and now we would like to understand the details of these interactions by studying specific groups," said Martin. "We really want to understand why some species can overcome the disadvantages of small size, while other species cannot."

The findings reveal that when it comes to bird species interactions, bigger isn't always better. Instead, some traits allow smaller species to triumph. This, in particular, is important to note when examining interactions within ecosystems.

The findings are published in the journal PLOS One.