Old trees must be protected to save the homes of more than 1,000
different bird and mammal species who nest, says a new study from the
University of British Columbia. Most animals can't carve out their own
tree holes and rely on holes already formed. The study found that
outside of North America, most animals nest in tree holes formed by
damage and decay, a process that can take several centuries.
The study, published this month in the journal Frontiers in Ecology and the Environment,
examined the holes birds and mammals were using for nesting around the
world. The research team, led by Kathy Martin, a professor in the
Faculty of Forestry at UBC, wanted to find out how the holes were
created and which species were using them.
In forests, tree holes are created either quickly by woodpeckers or
more slowly as trees age and begin to decay. Birds like owls, songbirds
and parrots, and mammals like flying squirrels and opossums, make homes
in the holes of trees because they offer safe environments for sleeping,
reproduction and raising young. Insects, snakes and amphibians will
also make use of tree cavities.
Martin and her research team found that on most continents -- South
America, Europe, Asia and Australia -- more than 75 per cent of the
holes used by birds and mammals were created by damage and decay.
"When wildlife depends on decay-formed cavities, they are relying on
large living trees," says Martin, also a senior research scientist with
Environment Canada. "Most trees have to be more than 100 years old
before decay cavities begin to form and often several centuries old
before large cavities or many cavities develop in one tree."
In North America, the team found very different results --
woodpeckers make up to 99 per cent of the cavities used by birds and
mammals.
Worldwide, tree holes are in short supply and many efforts to protect
the animals living in these holes have been focused on protecting
woodpeckers because it was presumed that they make most of the holes.
"Most forest policies help protect younger trees but promote the
harvest of older, larger, living trees -- the very trees needed by
cavity-nesting animals," says Martin.
The researchers monitored 2,805 tree holes in Canada, Poland and
Argentina between 1995 and 2010. They identified how the holes were
formed and every year checked to see if they were still usable.
"Some of the tree cavities in Canada were used 17 times in 13 years
by up to five different species," says Martin. "One tree cavity can
sustain a lot of wildlife over its lifetime."
Martin and her research team found that although woodpeckers live in
Argentina and Poland and make good quality holes, holes formed from
decay were used more extensively outside of North America because they
last much longer.
In Argentina, woodpecker holes would last only about two years, while
those made by decay could be used as homes for 25 years. In Poland, the
differences were less dramatic: the woodpecker-formed holes survived
for six years and decay-formed holes for 13 years. In Canada, where
animals nest in woodpecker holes, all holes last the same length of
time, about 14 years after they are created.
"The value of these large living trees needs to be recognized and we
need to ensure that a supply of these trees is retained especially in
tropical forest systems where decay-formed tree holes last for many
years and support a lot of wildlife."