`Big bird bills help with heat`

The evolution of bird bills is related to climate.

Updated: Jun 26, 2010, 13:19 PM IST

Washington: The evolution of bird bills
is related to climate, according to scientists who have found
that avians in hotter environments tend to have larger bills
while those found cooler environments have smaller bills.

An international team has examined bill sizes of a
diverse range of bird species around the world before coming
to the conclusion.

Their research, led by Dr Matt Symonds of University
of Melbourne, provides clear evidence that maintaining body
temperature in a bird`s natural environment may have shaped
the evolution of bird bills.

The size and shape of these distinctive structures
are usually explained by their role in feeding and mate
attraction. However, previous research shows bird bills have a
third, less appreciated function, as organs of heat exchange.

Co-scientist Dr Glenn Tattersall said: "We know, from
our thermal imaging studies that birds like toucans and geese
can lose a large amount of their body heat through their
bills. Unlike humans they don`t sweat but can use their bills
to help reduce their body temperature if they overheat.

"We then wondered whether this function had
evolutionary consequences, and sought to compare bill sizes
across a whole range of species."

The 214 species examined comprised diverse groups
including toucans, African barbets and tinkerbirds, Australian
parrots, grass finches, Canadian gamebirds, penguins, gulls
and terns.

"Across all species, there were strong links between
bill length and both latitude, altitude and environmental
temperature. Species that have to deal with colder
temperatures have smaller bills. This suggests that there is
an evolutionary connection between the size of the birds`
bills and their role in heat management," Dr Symonds said.

The findings have been published in the `American
Naturalist` journal.

PTI