Posted here are the core documents related to the task undertaken by the Biodiversity Committee to implement the resolution approved at the 2018 Annual Meeting “For community support for an island initiative to reduce or eliminate deer populations on Obstruction Island.” These include, beginning with the most recent and following a chironology backwards,
1. Letter #3 from the Biodiversity Committee
2. Letter #2 via the Biodiversity Committee from Ruth Milner, state biologist from WDFW
3. Letter #1 from the Biodiversity Committee
4. Fall Newsletter 2018 text related to the work of Biodiversity Committee
5. The resolution with background circulated for the 2018 Annual Meeting
6. Report on the effects of deer overbrowsing circulated to the community with the 2017 Annual Meeting materials.
(Obstruction Island Biodiversity Committee
Mailing #3 - Ecological effects of overbrowsing, January 4, 2019)
The Ecological Effects of Overbrowsing
There have been concerns about deer overpopulation on Obstruction Island and the
impacts that deer have on Island biodiversity. Ruth Milner, wildlife biologist with the
Washington Department of Fish and Wildlife (WDFW) has expressed her concerns
about Obstruction Island’s plant diversity and the impact that overbrowsing has on birds and other species that require a diverse plant community. This letter discusses the ecology of Obstruction Island, black-tailed deer (Odocoileus hemionus), and the
balance between them.
Deer Ecology - Diet
In the San Juan Islands, black tail deer favor shrub, wildflower, and some tree species,including Pacific madrone (Arbutus menziesii), Indian paintbrush (Castilleje sp.), cowparsnip (Heracleum lanatum), American yellowrocket (Barbarea orthoceras), pinkpurslane (Claytonia sibirica), fingecup (Tellima grandiflora), salal (Gaultheria shallon),Oregon grape (Mahonia nervosa) and thimbleberry (Rubus parviflorus) (Gaston et al.
2006). They avoid bryophytes (moss species) because they cannot effectively digest
the lignin-like compounds within them (Prins 1982).
Photo 1 (left to right): Indian paintbrush, Pacific madrone, salal, thimbleberry.
Island Ecology - Plants
Plant diversity on Obstruction Island is poor. Our second-growth forests lack the shrub
species typical in healthy Pacific Northwest forest habitats. These species, such as
salal, elderberry, red-flowering currant, etc. are shade-tolerant and adapted to grow
under a mature forest’s canopy. Because deer selectively browse on these shrub
species and cannot digest mosses, the understory of Obstruction Island is dominated by
moss species. Tree regeneration has also been disrupted by deer overbrowsing. In dry
forest such as those found in the San Juan Islands, Douglas fir would be the main
species in the old-growth forests with some western red cedar and western hemlock.
No saplings or seedlings of the main tree species - Douglas fir, western red cedar,madrone, grand fir, big leaf maple, and alder exist on Obstruction. The only tree
seedling on Obstruction is western hemlock and there are many areas of the island
where hemlock seedlings exhibit stunted growth.
Photo 2: Overbrowsing of shrubs has selected for a moss-dominant ecosystem on
Deer Ecology – Feeding Strategy
Another factor affecting deer health, aside from diet, is their browsing and movement
pattern and predation. Historically, deer populations in the San Juan Islands were
controlled by predators, such as the gray wolf, cougar, and bear. Predators were hunted
to extinction within the islands, mainly by farmers trying to protect their livestock. The
last gray wolf in the islands was killed in the 1860’s. Without population control, deer
have well exceeded the carrying capacity of the islands they inhabit, including Obstruction.
Deer tend to browse in a particular area until the food source in that area is depleted.
Then they typically move to other areas and continue the process of depleting that
particular patch (Long et al. 2013). In a mature and diverse forest, this feeding strategy
is sustainable. Seed banks in the soil, coupled with the recruitment of native species,
replace the depleted vegetation. Once this vegetation becomes mature enough it can
reproduce and replenish the seed bank that allowed it to grow. The patch can then be
sustainably harvested by the deer once again. The cycle can continue for an eternity
without effect on the biodiversity of that ecosystem.
This cycle has been broken on Obstruction Island. Because of the Island’s size and the number of deer on the island, patches of native vegetation are depleted before they are
able to replace their seed bank. The seed bank keeps producing plants, but the plants
are not able to mature long enough to reproduce and replenish the seed bank. Once a
seed bank is depleted, the vegetation that once occupied that area will no longer grow
there without intervention. Invasive, noxious, species like tansy ragwort (Jacobaeavulgaris) tend to move into these overbrowsed areas because they have evolved to
produce many times more seeds/spores and outcompete the native species that belong
there. Overbrowsing causes a cascade of negative impacts that are hard, and
sometimes impossible, to reverse. However, deer exclusion fences set up by some
islanders indicate that Obstruction Island still has the opportunity and seed bank to
support a rich plant community once again, but the clock is ticking.
Affected Birds, Mammals, and Insects
Overbrowsing of vegetation also has a cascading effect on species of birds, small
mammals, and insects that have historically occupied the Island. Obstruction Island is
approximately 218 acres in size and is able support a variety of habitats, including
mature coniferous forests, rocky shorelines and intertidal zones, bluffs, and outcrops.
Despite the variety of available habitat, O.I. supports less diversity of vegetation than
islands without deer (Milner Letter 2018). Obstruction Island lacks many songbird
species that are abundant on other islands without deer. Some species include the
rufous hummingbird, winter wrens, American goldfinches, sparrows, swallows, and
yellow warblers (Photo 3). Many of these species have similar habitat requirements -
plant diversity in the sub-canopy and shrub layers of their mature forests. These species
have been supported in part by feeders from many islanders, but are rarely if ever
spotted in the interior of the island. The island currently lacks the habitat to support
Photo 3: Left to right: Rufous hummingbird, yellow warbler, American goldfinch.
Pollinators rely heavily on plant diversity as a source of food and some rely on a denseshrub layer for ground-nesting habitat (i.e. bumblebees). Because Obstruction Island’s shrub layer is overbrowsed by deer, less pollinators are able to occupy the island and
pollinate plants (an important step in a plants reproduction cycle), further compounding
the problem. This is another cascading effect that overbrowsing has on wildlife.
Mammals that historically occupied the San Juan Islands include Douglas squirrel,
raccoon, black bear, cougar, foxes, bobcats, and badgers. Without the ability to
reintroduce predators on Obstruction Island, we must find another way to control our
Black-tailed deer are a serious threat to Obstruction Island biodiversity. Without
predation, deer have reached their carrying capacity on the island and created a
cascading effect of habitat loss that influences plant, bird, insect, amphibian, reptile, and
mammal species. There is indication that if deer populations can be controlled on the
island, native vegetation can be restored and species that have been affected by deer
habitat degradation can once again inhabit the island. If deer populations are not
controlled, Obstruction Island may lose the opportunity to replenish its historic
Gaston, Anthony J., et al. “Species-Area Relationships and the Impact of Deer-Browse
in the Complex Phytogeography of the Haida Gwaii Archipelago (Queen Charlotte
Islands), British Columbia.” Ecoscience, vol. 13, no. 4, 2006, pp. 511–522.,
Long, E.s., et al. “Conditional Daily and Seasonal Movement Strategies of MaleColumbia Black-Tailed Deer (Odocoileus Hemionus Columbianus).” Canadian Journal ofZoology, vol. 91, no. 10, 2013, pp. 679–688., doi:10.1139/cjz-2013-0034.
Department of Fish and Wildlife
PO Box 1100- 111 Sherman Street • La Conner, Washington 98257 • (360) 466-4345 FAX (360) 466-0515
November 19, 2018
Ms. Tracie Kempton
Obstruction Island Community (OIC)
You have asked for a biologically based opinion about the impacts of black-tailed deer on
Obstruction Island habitat. I visited Obstruction Island last summer to see how deer might be
affecting that site. Thus, my opinion is based on a site review of the habitat conditions on
Obstruction, versus simply extracting information from other islands.
It’s helpful to understand a little of the islands’ natural history prior to settlement by non-
indigenous peoples. The larger islands were populated by deer, wolves and cougars. On smaller
islands like Obstruction, deer would have colonized, a population would have developed, and
then predators would have moved in and either eliminated them or greatly reduced their
numbers. Thus, deer would come and go, giving plants a chance to recover from browsing. The
native vegetation was comprised of a large variety of plant species. The forest understory was
composed of low growing plants and layers of shrubs and young trees, all of which would have
provided multiple places for birds and insects to nest and thrive.
Settlers brought livestock and guns to the islands. Predators were deliberately wiped out because
they preyed on domestic stock and frightened settlers. The last wolf was reportedly shot on
Lopez around 1865. This left humans as the remaining predators available for deer control. In
the early days, they may have been somewhat effective at reducing deer numbers –taking as
many deer as needed to feed the family because hunting was a way of life for people living in
this rural setting.
However, as the human population has grown in the islands, so has the deer population. Dr.
Peter Arcese, an ecologist at University of British Columbia, estimates the population is at least
10 times higher than it was when predators existed in the islands. The results are highly evident
on Obstruction: the layering of plants that support an array of forest birds and insects does not
exist; the variety of native plants (or plant species in general) is greatly reduced, restricting the
number and variety of insects and birds that occur there. Conifer tree regeneration is not
occurring because deer have heavily browsed the young trees, making it impossible for them to
survive and grow to replace the older trees as they die out. In short, the natural habitat on
Obstruction Island is highly simplified and in poor condition. This is a result of heavy browsing
by lots of deer over many years.
This problem is not unique to Obstruction, but is common in the islands. I have several scientific
papers that I can provide on the impacts of too many deer on the islands, if your members are
interested. You can view a talk by Dr. Arcese here: https://www.seadocsociety.org/blog/video-
Frankly, the tools available to reduce deer numbers are limited. Sharp-shooters, trapping and
relocating, or various sterilization techniques are not viable options. Hunting will not instantly
solve the problem; it will take time if adopted.
Clearly, deer damage to island habitats is a complex problem. Adding the human dimension of
deeply held values increases that complexity enormously. I understand that values and attitudes
around killing deer, through hunting or other means are strongly held beliefs, and I respect those
perspectives. If the Obstruction Island homeowners would like to meet and discuss the issue in
depth I am available.
District 13 Wildlife Biologist
Washington Department of Fish and Wildlife
(Letter #1 from the Biodiversity Committee, September)
As you know from the Annual Meeting
and the recent newsletter, a committee has formed and convened to explore ways
to manage the deer population – for the health of the island, other wildlife
and the deer population.
As with any complex issue, it’s
challenging to present all the information at once and in one form. As a
committee, we have decided to provide you with information in a number of ways,
over a number of months – including emails such as this, access to the committee
to voice your questions and concerns and – if desirable – conference calls.
Our goal is to provide the community
with a plan to vote on at the Annual Meeting 2019. This first email provides
you with some key information, and we will dive deeper in subsequent emails.
Why we should manage the deer population
Controlling deer numbers on
Obstruction Island and elsewhere in the San Juan and Gulf Islands has
exceedingly important ecological merit. An indirect effect of
exterminating predators (mountain lions and wolves) in the islands has been a
significant loss of plant and animal species variety and abundance. Peter
Arcese (UBC) and colleagues have a plethora of studies that show the negative
and far-reaching effects of too many deer on island flora and fauna.
· A drastic decline in the number and
variety of birds, pollinators, and invertebrates is found on islands with high
deer populations and the resultant little or no shrub layer.
· Too many deer are causing or have
caused iconic island species and communities to go extinct.
o The large islands do not have
wildflower meadows that once were so common.
o Mature madrone still exist, but they will
die out within the next 50+ because there is no regeneration or
recruitment. Madrone are a favorite food of deer.
How and why have we gotten to this point?
Removal of apex predators in the
islands allowed black tail deer to multiply beyond the carrying capacity of the
islands. In the back to earth movement in the 1960s, many people moved to
the islands with an environmentally friendly ethos that shunned hunting.
This non-hunting attitude greatly
reduced or eliminated any control on island deer populations. Ironically,
letting deer multiply has had a devastating ecological toll on native plant and
animal communities. Until recently, we didn’t realize what’s missing on Obstruction
Island because we couldn’t see or hear it. However, on Jack &
Dianne’s place (lot 48 at the southern end of the island) is fenced to keep the
deer out. The growth of native vegetation—wildflowers, shrubs, tree
seedings and madrone re-sprouting—in less than a decade is phenomenal.
Are there other methods to control
the deer population?
There are 3 other approaches, all of
which are costly, ineffective or out of our control:
· Sterilization. It’s costly; It is only effective if every female on island
is sterilized, and not practical.
· Catch and Transplant. It’s costly, and there is no government program or staff
available to implement
· Predator Reintroduction. WDFW would need to be the lead on this program.
How many deer can live on ObstructionIsland without causing damage?
Ultimately, 7 deer or fewer on
Obstruction Island – as an intermittent population. Rather than counting
the number of deer, which local wildlife biologists find is difficult and not
accurate, we could measure ecological success in deer stewardship through plant
species diversity and tree species regeneration metrics.
Consider a pilot program to decrease deer through hunting
For the pilot deer
hunting project measures of success could be:
· Is hunting an effective stewardship
· How does hunting impact the
· Are some islanders more negatively affected
than others? Is there a way to mitigate or eliminate this negative impact?
· Is hunting logistically do-able on
· Do hunters like this form of
The time to act is NOW.
Small private islands, such as Obstruction, have the best chance of controlling
deer populations and restoring native flora and fauna. We are proposing
that our small island community attempt to show other island communities that
something can be done to stave off extinction our iconic island ecosystems.
We want Obstruction to be a vibrant
island, one full of life rather than slowly dying. Seeing a Nootka rose
in bloom, bright green spring leaves, a flower along a trail; hearing song
birds in the spring…would bring us (and many other islanders) great joy.
As we said, we will be reaching out
to the community over the coming months with information, and we welcome your
questions and reflections in order to craft the best proposal we can to bring
to the community.
Please don’t hesitate to contact any
of us. Your questions will help us provide you with the most relevant information
Tracie Kempton - [email protected]
Catherine Houck - [email protected]
Sue Clement - [email protected]
Carsten Stinn - [email protected]
Kellen Maloney - [email protected]
If you’re interested in viewing a talk about deer in the islands, check out
Ruth Milner’s talk.
(Selection from the September Fall Newsletter 2018, a preliminary report on developments over the summer as a aftermath to resolution approved at the May Annual Meeting)
Annual Meeting Deer Resolution, Follow-up activities
At the Annual Meeting 2018 the community voted
to research ways to reduce the number of deer as a way to support reforestation
and regenerate woodland habitat. This
is an area that has generated considerable research and experimentation across the country since
exploding deer populations and their attendant effects—over-browsing and
habitat destruction, tick infestation and tick-borne disease—has become a
national problem. A variety of solutions
have been explored such as birth-control and transportation but with little
success. The consensus is that the only
way to limit the damaging impact of too many deer on habitat is to reduce or
eliminate the deer. The research especially supports this solution for
black-tailed deer, our local species, since they are territorial, live within a
very limited range, and are slow to recolonize an area once cleared.
Reduction of the black-tailed deer population would
involve opening a portion of the island to a hunt. The island’s common lands
(the 60 acre center) and/or individual lots with the owner’s written
permission, could be open to controlled hunting. In order for us to do that would require
amending the covenant #12 that prohibits hunting and the discharge of firearms
on Obstruction Island. A possibility
would be to treat this initiative as a temporary exception, which would still require
the 75% approval by the island community necessary to amend a covenant. A resolution to enable such an exception to
covenant #12 might look something like this:
“Hunting and the discharge of firearms is not permitted on
for the purpose of reducing deer over-browsing and fostering woodland
and habitat regeneration, reservation-based and time-specific hunts to be
scheduled and regulated under the auspices of the state Department of Fish and
Wildlife. This exception shall only be
in effect between [specific dates], unless renewed by a 75% vote of the
This is just a sample and not the specific
wording of a resolution anyone has agreed upon, but it exemplifies key elements
that could be applicable such as terms that would be negotiated with the state
Department of Fish and Wildlife (WDFW} and a specific time within which this
exception would be permitted.
In early June as a follow-up to the Annual
Meeting resolution, Tracie Kempton hosted a delegation of WDFW personnel,
including Ruth Milner, the regional biologist, and Rob Wingard, the private
lands biologist, for WDFW. Also included
in the group were two enforcement officers and four islanders. During the visit, several key pieces of
information became clear:
--the terms of any hunt (who would participate,
how many days, and where) would be negotiable between WDFW and the island, and
WDFW would tailor the conditions to our demands. For any such plan to go forward would require community approval
through a vote at the Annual Meeting or a mail-in ballot.
--a hunt would be by reservation only. Only licensed hunters would be allowed on the
island who had applied for access, had a reserve time granted and been approved
by WDFW, and would be readily identifiable.
Hunters would be assigned to a specific area within which they would be
required to remain and hunt. Any
activity would be supervised by a huntmaster who would track hunters and keep a
tally of any game taken.
--the island could require that specific days
be set aside for islanders and friends only, though for this also hunters would
have to be licensed, the times reserved, and the hunt supervised by a
--a hunt could be limited in area ( i.e. to the
common lands in the island’s center, and/or private lots with the owner’s
--in accord with San Juan County restrictions: 1)
the hunt would be shotgun only or bow hunt; that is projectiles with a limited
range, and 2) no hunting can occur on private land without written permission
of the owner.
The commentary above and the visit from WDFW
biologist is in the vein of the research called for by the community
resolution, a scan on what would be feasible and its parameters. Any subsequent
action is yet to be determined and will require community approval. At the Annual Meeting several islanders
volunteered to pursue this issue and we will be hearing from them as their
(Proposal circulated with materials for the Annual Meeting 2018, moved, seconded, and approved ““For community support for an island initiative
to reduce or eliminate deer populations on Obstruction Island.” As a result, the Biodiversity Committee was formed
of island volunteers to research the issue and develop further initiatives.)
Wildlife management: Deer
We were first alerted to the effects of over-browsing about a decade ago by
Caroline Buchanan’s article, “The Ecology of a Small Island”. Caroline noted that virtually no seedlings
survived for forest regeneration.
Madronas, maples, firs, cedars, alders were browsed back at first
leafing. In more recent years we have
benefited from our resident conservation biologist Catherine Houck’s
presentations. These have dramatically
underscored over-browsing’s devastating effects on habitat for
birds—particularly ground nesters and those that depend on underbrush or low and
middle canopy—and reptiles, amphibians, and insects. The relative desertification radically
disrupts the regenerative plant and forest cycles while also diminishing the
biological diversity that a small island like Obstruction could support.
Exploding deer populations are a problem
nationwide and over the past few decades significant research has been
accomplished on deer numbers, behavior, and environmental impact. Population numbers on black tailed deer, the
local species, have been harder than most to pin down since it keeps to its
forest habitat more exclusively than white tailed deer or elk. The forest habitat makes spotting and
counting the deer more difficult. There
have been detailed studies, however, on our neighboring island Blakely by
researchers associated with their Seattle Pacific University biological station. Blakely at seven square miles supports
650-700 deer. Given our area, one-third
of a square mile, that would indicate around thirty deer on Obstruction.
Two salient points in this recent research
argue for the benefit and viability of an effort to reduce a population like
Obstruction’s. First, island
overcrowding is not good for the species itself, the result of nutritional
deprivation. This is indicated by:
· the small size and slow
growth rates of island deer
· the strikingly low incidence
of fawn survival and
· the rarity of twin births
compared to fawn survival and twin birth figures in healthy populations.
Secondly, the discovery that black tailed deer
cluster in small family groups and feed within relatively confined areas. Thus, once a territorial area is cleared,
recolonization by a successor population is very slow, if at all. In cases studied recolonization has been suspended
by as much as a decade or more.
These factors contribute to the viability of
Obstruction as a laboratory island which could support an effective reduction
campaign. The goals would be long-term relief from the
effects of overbrowsing and opportunity for sustained reforestation and habitat
Resolution For community support for an island
initiative to reduce or eliminate deer populations on Obstruction Island. This would first involve research to determine
feasibility: result and consequent actions recommended to be reported back to
the community by the Annual Meeting, 2019. The research would include at the
· exploring the need and
procedure for a vote to suspend or make an exception to the island’s covenant
against hunting. This may require consulting an attorney.
· To check with San Juan County
officials regarding ordinances etc that might impact or shape the initiative
· To consult with State Fish
and Wildlife to determine ways to proceed and any limitations posed by state
· To develop a budget for the
· To seek grant support
proposing Obstruction as a laboratory island for studying the most effective
practice for deer reduction in a confined area and also its long-term
consequences, both in terms of habitat recovery and recolonization.
Note: a very interesting discussion of this
issue occured on Orcas this Fall: Ruth Milner of WA Fish and Wildlife
presenting to the SeaDoc Society. Access
to the presentation, an hour and quarter video, is available at:
The talk and discussion is also available on
You-Tube by searching: “Ruth Miner Rising Deer Populations on the San Juan
Should the video length be discouraging, an
effective summary of Milner’s key points
was represented in an Island Sounder article:
We encourage you to check out one of these
resources as background for the Annual Meeting.
Report distributed with AnnualMeeting materials 2017
Deer Browsing on Obstruction Island
A State biologist estimates
that, on Obstruction Island, we have one deer for every 7 or 8 acres—a
population of 27-31 deer. Understory and
shrub layers are absent from the entire island. Seedlings and “saplings”
of western hemlock are heavily browsed. Seedlings or sapling of other
native tree species other than western hemlock and a few lodgepole pine (such
as western red cedar, Douglas fir, madrone, red alder, big leaf maple, and
rocky mountain maple) are absent. Based on research conducted in the Gulf
and San Juan Islands, the sustainable population of deer on our island is only eight
or nine. *
The Hart’s, Lot 48, erected
a deer excluding fence about 4 years ago; seedlings and saplings of Douglas fir,
western red cedar, and madrone are prolific, not to mention the remarkable
shrub growth and shoots from the base of madrone trees. The forbs and
grasses within this enclosure are a sight to behold, especially in comparison
to the vegetative void on the deer accessible side of the fence. These
observations have raised many questions for some folks on Obstruction Island.
Catherine Houck contacted Eric
S. Long, Professor of Biology of
Seattle Pacific University, who does research
on deer on Blakely Island. He has
provided us with these answers to the following questions:
1. Are we correct
in assuming that deer populations were much smaller in the past allowing trees
species to become established? When and how did the deer population on
Obstruction Island or the San Juan Islands in general get to the point where
their browsing is limiting tree regeneration?
Yes, deer populations
were likely smaller in the past, for a couple reasons. First, there
were probably predators in the San Juans, prior to us exterminating them.
There were likely coyotes, bears, and possibly cougars (though the smaller
islands couldn't have sustained cougar or bear populations). Also, prior
to timbering, the islands had mature trees with closed canopy. Very
little sun would have reached the ground, so forest regeneration would have
been very limited. Virgin forests have pretty restricted ground cover, so
deer populations are low in mature forests. So, before the forests were
cut for timber and housing, there just wouldn't have been much food for deer.
Once timbering opened the canopy, lots of regeneration occurred, causing
the deer population to explode in the absence of predators. Now, there's
nothing to knock the deer populations down (other than their own over-browsing)
to give trees and other vegetation relief from the browsing pressure.
2. How many other islands have
been or are in a similar vegetative state as Obstruction Island?
Pretty much any
island big enough to sustain a deer population (or regularly attract transient
deer) will suffer from over-browsing. Some small islands that have lacked
deer look totally different from the other islands with deer. (They look much more like the fenced
situation you described).
are some land managers in various locales in the San Juan and/or Gulf Islands
doing to control deer populations? Are they “successful”? What
measures do they use to control deer and how do they measure the changes?
There's currently no
good way to regulate deer populations in the San Juans. In the absence of
predators, hunting would be the most likely answer. We're nowhere close to reintroducing predators (though I keep joking about a"Rent-a-Wolf" program). That said, coyotes have started to
naturally recolonize some islands. This is good news for foresters and
bad news for deer. Since most of the San Juans are privately owned,
hunting access is really limited (and politically charged). Obstruction is probably too small maintain a
4. We don’t observe a lot for the deer to eat on
Obstruction Island, especially in
comparison to the vegetation on Orcas Island and
Blakely Is just across two small channels. Why do the deer stay on
Obstruction Island rather than swim to greener islands?
probably getting a lot of transient deer. (Deer swim.) So, if a
deer swims off Obstruction, there's probably one waiting to get on. (One
of my radio-collared bucks swam from Blakely to Decatur and back again twice.
He then did a round trip to James Island.) And, yes, Blakely looks
green - but there's actually very little for deer to eat on Blakely. The
green is mostly from salal, hemlock, tansy ragwort, foxglove, etc. None
of those are preferred food. Despite the great canopy cover of Douglas
fir, cedar and madrona, it's incredibly challenging to find saplings of these species, just as you note. We're basically just getting hemlock
Over-browsing by deer is a
primary cause of the decline we are witnessing in plant and animal diversity in
deer inhabited islands in the San Juans. As we learn more about our fragile environment
we are faced with decisions that will affect whether we can regenerate and
sustain our ecosystem, or allow biodiversity to continue to decline.
There is no easy solution,
but we hope to open the conversation. We
are proposing putting in two deer exclusion enclosures, perhaps 10 x 10’ each,
in the center of the island to quantify the effects of no browsing activity. Fish and Wildlife say that hunting is the only
effective way to limit populations
While we contemplate the
issues, we all can help by not feeding or providing a fresh water source for
deer and raccoons. While these small
measures will not reverse the degradation we are witnessing they are a first
step in preserving the beauty of our island.
*Declines in forest and
woodland birds have largely been attributed to habitat loss and fragmentation.
In the past decade, however, the potential for herbivores to influence bird
species abundance and community composition via their direct impact on vegetation
structure has also been recognized. We tested the hypothesis that deer
influence vegetation structure and bird assemblages in a large island
archipelago in western North America using surveys of 18 islands with deer
densities ranging from 0 to over 1 deer/ha. Amongst these islands, reduced
predation and hunting pressure has allowed deer populations to increase
above those likely to have
existed in pre-European times. Our results support a growing body of evidence
that deer regulate both the cover and architecture of understory vegetation
which in turn profoundly affects island bird assemblages. Deer-free islands supported
the most abundant and diverse bird fauna. Iconic songbirds such as the rufous
hummingbird, song and fox sparrow were abundant on islands with no deer but
substantially reduced on islands with high deer densities. Only one bird
species, the dark-eyed junco, preferred moderate and high density deer islands.
Our observations suggest that current cohorts of palatable shrubs on islands
with high deer densities are relatively old and potentially represent an
impending extinction debt, where the full effects of high deer density on
island biota may take decades to fully unfold. Our results suggest that deer
densities below a threshold of 0.1 deer/ha should allow native vegetation to
recover and a rich and diverse bird species assemblage to persist. We suggest
that adaptive management be used to test the validity of this threshold, and
that without active management of deer abundance, local extinctions of native
flora and fauna appear likely to accelerate.
Martin, T.G., et al.
Browsing down our natural heritage: Deer impacts on vegetation structure and
songbird populations across an island archipelago. Biol. Conserv. (2010All
Deer browsing impact on forest vegetation cover
No Deer, Patos Island Moderate Deer density, Wallace Island
High deer density (Sidney