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August 2011

The Sheep are Mightier than the Mauna Kea Silversword

Everyone loves a Cinderella story, one in which the underdog overcomes the endless odds stacked against him/her and ends up victorious.  Hollywood has made millions with movies depicting heroes that range from boxers making it big to sweet-hearted step-daughters overcoming evil step-mothers to live happily ever after.

There are so many situations ripe for a Cinderella story in the natural world of plants and animals.  One intriguing plant in particular, the Mauna Kea silversword, is a beautiful and unique plant struggling at the brink of extinction.  Recovery of this plant would make a very happy ending.

Mauna Kea silverswords are also called `āhinahina in Hawaiian, which loosely translates to “light blue, gray or slate”.  The `āhinahina are a type of endangered plant that grows only on Hawai’i’s Big Island on Mauna Kea, a  dormant volcano and the tallest mountain in the Hawaiian Chain.  The `āhinahina is a beautiful plant that inspires awe in the hearts of most that see it, much like its popular cousin, the sunflower, which has a similar effect on its viewers.  Sadly, the popular Mauna Kea silversword is struggling to exist.

Part of what makes the Mauna Kea silversword so unique is its biology.  The silversword gets its name from its leaves, which are shaped like daggers and are densely covered with layers of silvery hairs.

 

A Mauna Kea silversword
A Mauna Kea silversword.  Photo credit: Jack Jeffrey

Silversword on rocks
Mauna Kea silverswords are easy to identify as their silver color makes them pop out from their surroundings. This plant is found within a fenced enclosure protected from ungulate grazing.  Photo credit: Rob Robichaux

 

Most silverswords flower only once, after growing for 30 – 50 years.  At maturity the silversword can produce a 6-foot-tall flowering stalk with hundreds of flowers.  Since silverswords sometimes grow for many decades before flowering, it is relatively rare to see one in bloom.

Unfortunately, the Mauna Kea silversword is a favorite snack for introduced Mouflon and feral sheep and goats (collectively called ungulates) that roam around Mauna Kea.  When ungulates graze on silversword, the silversword will likely not survive. 

The ungulate population persists, which puts silversword survival in jeopardy (as well as palila and māmane mentioned here). In fact, many of the silverswords that have survived over the years have done so because they are hanging on cliff faces where the ungulates can’t reach them. 

Several agencies partnered up with a goal of propagating the Mauna Kea silversword. For more details, click here.

The efforts to propagate the Mauna Kea silverswords have had varying degrees of success.  In the 1960’s fences were placed around areas with budding silverswords in an effort to protect them;

    Click to play a video showing harmful ungulate grazing of endangered Mauna Kea silverswords. This area is unfenced and therefore not protected from ungulates, leaving the silverswords at risk.


however, the ungulates were able to jump the fences and consumed the plants.

Later silverswords were outplanted in 4 areas (near Pu’u Nanaha, Skyline jeep trail, Waipahoehoe gulch and Pohakuloa) but these populations were limited genetically and accessible to the ungulates, so the plants had a low survival rate of 34%.  More recently, in 1999, more than 2,500 silverswords were outplanted on Mauna Kea.  

Click to play a video of feral sheep on Hawai`i island.    

The reintroduced silversword populations must be hand-pollinated to ensure genetic diversity—a task that requires time, energy and oversight.

These conservation efforts have resulted in an increase in the total population of silverswords.  However, the remnant naturally occurring population has declined.  For more information, click here

It stands to reason that while we can help the overall silversword population by growing and planting them in secure environments and hand pollinating them, we won’t help the naturally occurring population grow unless we stop the ungulates from consuming them.  Silverswords require fencing to exclude the ungulates.

The Mauna Kea silverswords can be compared to the old growth forests in that they are beautiful and valued and lead impressively long lives but they are still vulnerable and once they are gone, there is no getting them back.  Future generations will feel the loss, similar to the loss we currently feel for old growth forests, if we lose the Mauna Kea silversword.  

To contact the U.S. Fish and Wildlife Service about this piece or to report a violation you have witnessed, please go to www.fws.gov/pacific/lawenforcement/ and click on the “contact us” link at the top of the page.

 

 

 

Mauna Kea silversword on cliff face.
A Mauna Kea silversword survives on a cliff face out of reach of grazing ungulates.  Photo credit:  U.S. Fish and Wildlife Service

Old Growth Forests in Oregon
Old growth forest.  Photo credit: Wikimedia Commons


Flowering Mauna Kea Silversword found in a fenced enclosure built in 1975.
Flowering Mauna Kea silverswords found in a fenced enclosure built in 1975 and protected from ungulate grazing.  Flowering stalks can grow up to 6 feet tall and produce hundreds of flowers.  Photo credit: Rob Robichaux

 


 

Last updated: December 3, 2013

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