CHANNEL ISLANDS NATIONAL PARK

The Decline of the Island Fox

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<td colspan="7"><p><strong>Counting Foxes:</strong></p>
<p>Since 1993, the National Park Service has monitored the population of
Island Fox on San Miguel Island. Each summer, foxes were trapped and
tagged. When each fox is first captured, it is implanted with a device
about the size of a grain of rice called a passive integrated
transponder tag, or "PIT" tag. The tag gives each fox a permanent,
unique number that can be read with a special scanner and allows
scientists to monitor individual foxes over the years.</p></td>
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<td colspan="6"><strong>The Warning:</strong><br />
Park biologists estimated there to be over 400 foxes on San Miguel in
1994, but by 1995, an alarming decline had begun. With each passing
year, fewer foxes were trapped in the monitoring grids. At the same
time, rangers and visitors reported seeing fewer live foxes and more fox
skeletons and carcasses. By 1998, the San Miguel population was down to
a few dozen. Similar declines occurred simultaneously in the island fox
populations on neighboring Santa Rosa and Santa Cruz Islands.</td>
<td colspan="4" rowspan="4"><img src="media/image1.png"
style="width:3.75278in;height:2.8in" /></td>
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<td colspan="4"><p><strong>Looking for Answers:</strong></p>
<p>In fall 1998, National Park Service biologists initiated a
radiotelemetry study of island foxes on San Miguel Island to determine
causes of mortality. Of the 15 radiocollared foxes, 5 were believed to
be killed by golden eagles and 2 died of other causes. This confirmed
the results of an earlier study on Santa Cruz, where golden eagle
predation was identified as the cause of death in 21 of 29 fox
carcasses. This level of golden eagle predation is considered by
scientists to be unnatural because golden eagles are not native to the
Channel Islands.</p></td>
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<td colspan="6">Until recent years, the island fox occupied the top
position in the island food chain with no natural predators. Scientists
found the first <a href="../eaglepics.htm">golden eagle</a> nest ever
recorded on Santa Cruz Island in 1999 and believe they have taken up
residence to hunt introduced pigs and sheep. Most likely deterred in the
past by the native <a href="../baldeagle.htm">bald eagle</a>, golden
eagles did not begin their visits to the islands until their larger
fish-eating relatives were wiped out by DDT, hunting, and egg
collection. With sharp talons, swiftness of flight, and 4 times the body
mass of a fox, golden eagles can easily prey upon the unsuspecting fox.
Interestingly, the first documented decline on San Miguel in 1995
coincides with the first golden eagle sighting on the island.</td>
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<td colspan="6">However, aerial predators are not the only ones facing
the island fox. Internal threats like disease and parasites also pose
serious problems. Lab tests on island foxes have revealed harmful
parasites such as heartworm and hookworm. Canine diseases like
parvovirus and adenovirus have also been detected in some foxes. In just
one year, on privately-owned Santa Catalina Island, about 90% of the fox
population was recently lost due to canine distemper virus. Due to their
insular existence, island foxes have no built up immunity to parasites
and diseases brought in from the mainland and are especially vulnerable
to those a domestic dog might be carrying. In addition, it is extremely
difficult to vaccinate against or treat foxes for these parasites and
diseases in the wild. For this reason, pets are not permitted in Channel
Islands National Park [36CFR2.15(a)].</td>
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<td colspan="3"><a href="../history.htm"><strong>Natural
History</strong></a></td>
<td><a href="#LookingforAnwers"><strong>The Decline</strong></a></td>
<td colspan="2"><a href="../fox3.htm"><strong>Saving the
Fox</strong></a></td>
<td colspan="2"><a href="../Fox4.htm"><strong>How to
Help</strong></a></td>
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