Chickadee, Nuthatch Presence In Conifers Increases Tree Growth,
Says CU-Boulder
  Kirk Johnson
  Sep 13, 2007 13:34 PDT 

Thought this might be of interest.

Chickadee, Nuthatch Presence In Conifers Increases Tree Growth, Says
CU-Boulder Study

Chickadees, nuthatches and warblers foraging their way through forests have
been shown to spur the growth of pine trees in the West by as much as
one-third, according to a new University of Colorado at Boulder study.

The study showed birds removed various species of beetles, caterpillars,
ants and aphids from tree branches, increasing the vigor of the trees, said
study author Kailen Mooney. Mooney, who conducted the study as part of his
doctoral research in CU-Boulder's ecology and evolutionary biology
department, said it is the first study to demonstrate that birds can affect
the growth of conifers.

"In a nutshell, the study shows that the presence of these birds in pine
forests increased the growth of the trees by helping to rid them of damaging
insects," said Mooney. "From the standpoint of the trees, it appears that
the old adage, 'the enemy of my enemy is my friend,' holds true."

A paper on the subject by Mooney was published in the August issue of
Ecology, a monthly science journal. Mooney, who received his doctorate from
CU-Boulder in 2004, will become a biology department faculty member at the
University of California, Irvine, in fall 2007.

In the study, Mooney used mesh netting to exclude birds from ponderosa pine
limbs in the U.S. Forest Service-managed Manitou Springs Experimental Forest
northwest of Colorado Springs for three years. The results showed that
branches on 42 trees rigged to exclude birds had 18 percent less foliage and
34 percent less wood growth by the end of the study.

Mooney collected about 150,000 insect specimens from the mountain study
area, identifying more than 300 separate spider and insect species
collectively known as arthropods. The trees used in the study were set up to
exclude birds, ants, or both, since ants also can have significant impacts
on other arthropods, he said.

"The study indicates that pine canopies are very complex systems with an
unexpected level of biodiversity," said Mooney. "Forest managers really need
to look at the big picture of ecosystems and not just focus on trees when
implementing regulations aimed at encouraging the growth of healthy

The study also has implications for large areas of the West ravaged by
forest fires in recent years, he said. A number of once formidable stands of
mature ponderosa have been burned and logged and subsequently replaced by
smaller pines that offer limited breeding opportunities for cavity-nesting
birds like chickadees and nuthatches, which nest and lay their eggs in the
holes of large trees and dead snags.

"This is a very rigorous study that essentially shows that even modest
little birds like chickadees and nuthatches can help improve the heath of
the trees, which are the monarchs of the forest," said CU-Boulder biology
Professor Yan Linhart. Linhart was Mooney's doctoral adviser at CU-Boulder
and also co-authored a study with Mooney in 2006 in the journal Animal
Ecology. The study compared the effects of birds on pine with their effects
on dwarf mistletoe, a parasitic plant on ponderosas throughout the West.

Mooney said the activity of the birds also was shown to change the chemical
"flavor" of the trees, which may have implications for infestations by
damaging insects like bark beetles that have ravaged pine forests in the
West. Chemicals in trees known as terpenes, which give vegetation
distinctive odors, have been implicated in the resistance of trees to
parasites and plant-eating insects, he said.

By removing insects, the birds indirectly altered the terpene composition of
pine tissues, said Linhart. The alteration of terpene "flavor" can have wide
ranging effects, since terpenes influence decisions that creatures like bark
beetles, porcupines and squirrels make when deciding which trees to eat,
said Linhart.

"Terpenes act a bit like an immune system by essentially fending off attacks
by birds and mammals," said Linhart. "One of the fascinating results of this
study is that birds affect how this immune system functions."

The study also showed that chickadees and nuthatches disrupt a mutually
beneficial relationship ants have with aphids, which feed on plant tissue
known as phloem sap that carries nutrients through the tree, Mooney said.
While some ant species "tend" aphid colonies -- protecting them from
predators in exchange for their carbohydrate-high "honeydew" secretions -
feeding activity by birds can disrupt this relationship, triggering aphid
population decreases and increases in tree growth.

"These ponderosa forests have very complex food chains," Linhart said. "In
essence the nuthatches and chickadees act as tree protectors, keeping check
the insects that can have deleterious effects on forest vigor."

The birds in the study included the mountain chickadee, the red-breasted
nuthatch, the pygmy nuthatch and the yellow-rumped warbler. All but the
warbler are year-round residents of ponderosa pine forests in Colorado.

"More than anything, this study underscores the importance of preserving the
ecological communities in the forest, and not just the trees," Mooney said.

The study was funded by the USFS Rocky Mountain Research Station
headquartered in Fort Collins and by CU-Boulder. Mooney was a postdoctoral
researcher at Cornell University in 2006-07.

Contact: Kailen Mooney, 

Yan Linhart,

Jim Scott, 
RE: Chickadee, Nuthatch Presence In Conifers Increases Tree Growth,   Andrew Joslin
  Sep 14, 2007 09:18 PDT 

What a great study. Confirms what many of us who have observed the small
gleaning bird species have suspected was true. The part about bird
foraging changing the terpene composition of the pine tissue is also
very interesting.

I had the good fortune to be up in the top of a ponderosa in the
foothills of the Rockies northwest of Boulder a couple of weeks ago. And
better yet to have Mountain Chickadee and Pygmy Nuthatch dancing around
in the surrounding branches.

Speaking of terpene composition and "tree flavor" it was very
interesting to see that specific ponderosa were heavily targeted by
Yellow-bellied Sapsuckers year after year while nearby ponderosa were

Andrew Joslin
Jamaica Plain, MA