Subject: Question about plants for birds
Date: Feb 6 20:29:53 2003
From: Kelly Cassidy - lostriver at completebbs.com


In gardening for wildlife, I think selection of specific plant species is
overemphasized, while the importance of detritus and vegetative structure is
virtually neglected.

The Hubbard Brook Experimental Forest, a deciduous forest in New Hampshire,
is probably the most exhaustively studied ecosystem in the world.

Most everyone has seen the food web models displayed in every basic biology
text. Plants use the energy from sunlight to make more plant biomass.
Herbivores eat plants. Carnivores eat herbivores. As an afterthought, such
diagrams have lines going from plants, herbivores, and carnivores to
detritus. (From air to dust, you might say.)

At Hubbard Brook, a very small amount of plant material gets eaten by
herbivores every year. The vast majority of the plant material created with
the energy of sunlight falls to the ground in fall as leaves. Fungus,
bacteria and soil invertebrates munch on the leaves. Other invertebrates
eat the detritus eaters. Vertebrates eat a combination of "live" plant
material, detritus eaters, and the eaters of detritus eaters.

Birds, as a group (obviously, proportions vary by species), eat 1.4
kilocalories per square meter per year (k/m2/y) of fruit and seeds. They
eat 6.0 k/m2/y of invertebrates, most of whom are eating detritus. In other
words, more that three times as much of the food birds eat comes from
invertebrates as fruits and seeds. Certain groups of animals, like shrews
and salamanders eat almost nothing but invertebrates, which are mostly
eating detritus or eating detritus eaters. Deer and rabbits are among the
few vertebrates living almost entirely on plant material before it becomes
detritus.

There are occasional years when most of the plant material is eaten before
it becomes detritus; about every decade, Hubbard Brook has outbreaks of
defoliating caterpillars such as Heterocampa guttivita (Saddled Prominent).
(Many birds have increased fledgling survival during these years.) In most
years, though MOST PLANT MATERIAL IS NOT EATEN UNTIL AFTER IT BECOMES
DETRITUS. Pardon me for shouting, but I think this is very important when
you are trying to create habitat in an urban yard, because raking leaves is
practically an urban obsession. Of course, if you live east of the
Cascades, and fire is an issue, you need to think very carefully about
whether you might be creating a fire hazard if you don't rake your leaves.

If it seems counterintuitive that most plant material falls to the ground
before it's eaten (why wouldn't critter prefer their food fresh?), consider
that plants are not as defenseless as they look. They cover their leaves
with unpalatable hairs, spines, and wax and make all sorts of bad-tasting or
downright poisonous chemicals to discourage chewers. They only make
palatable those things they want an animal to eat, like edible fruits and
nectar.

I don't know how ecosystems other than Hubbard Brook compare in terms of how
much energy flows through detritus before it gets to vertebrates. No
ecosystem has been more intensively studied over as long a period of time as
Hubbard Brook, but it is highly likely that detritus is just as critical in
most others.

So try to encourage those urban habitat makers to leave those leaves where
they fall, or at least to not rake them up and have them hauled off.

For those that are still reading, and care, the Hubbard Brook information is
from:

Gosz, J. R., R. T. Holmes, G. E. Likens, and F. H. Bormann. 1978. The flow
of energy in a forest ecosystem. Scientific American. 238:92-102. (A very
readable, classic paper in ecology.)

and

Holmes, R. T. and T. W. Sherry. Ecological factors influencing biodiversity
in northern hardwoods ecosystems: contributions of long-term studies of bird
populations at Hubbard Brook. Biodiversity at the HBR Long-term Ecological
Research Site. I couldn't figure out the year of this one, but it was post
1998 and is on the web at:
http://atlantic.evsc.virginia.edu/auto_docs/LTER_biod97352439.html

Structure is important, too. An isolated serviceberry (Amelanchier
alnifolia--a popular "wildlife" shrub) on a patch of lawn isn't much
habitat. A combination of grass, shrubs, mixed forbs, and trees growing
together in some manner that sort of mimics the structure of some local
wildlife community will be more attractive to wildlife than a random
collection of shrubs with berries that are favorites with wildlife habitat
book writers.

Kelly (long-winded) Cassidy
Pullman, WA


----- Original Message -----
From: "Jina Chan" <jina at u.washington.edu>
To: <tweeters at u.washington.edu>
Sent: Thursday, February 06, 2003 10:26 AM
Subject: Question about plants for birds


> I'm starting my graduate school research, and I'd like to quantify what
> plants are best for urban bird habitat in the Puget Sound area. I'm only a
> beginner birder myself, so I thought I'd ask: are there particular plants
> (ornamental plants are fine; doesn't have to be native) you've seen used a
> lot by birds in the city? And was there anything that surprised you or
> was unusual?
>
> -- Jina Chan <jina at u.washington.edu>
> Graduate Student, Center for Urban Horticulture
> University of Washington, Seattle, WA, USA