Restoring Habitat for the Mission Blue at Hawk Hill

Mission blue larvae enter a hibernation state called diapause that lasts throughout the summer, fall, and winter months. Then, newly metamorphosed mission blue butterflies emerge and journey to find their required host plants. They mate and die within a single week.

Will Elder/NPS

The Mission Blue Butterfly's Story

Although Hawk Hill is primarily known for migrating raptors, the wings of a much smaller creature known as the mission blue butterfly are what keeps restoration ecologists returning to the site. One of the first invertebrates to be protected under the Endangered Species Act, this small butterfly is an important ecological player within Golden Gate’s grasslands. Though they are in our park year-round, they’re most noticeable for only six to eight weeks of the year when the adults can be seen flying about.

Mission blue numbers plummeted in the mid-90s after a fungal pathogen attacked their host lupines. Mission blues lay their eggs on three species of lupine that are the sole food source for their caterpillars. These lupines grow amongst fields of coastal prairie and scrub, but because lupines thrive at recently disturbed sites, good lupine habitat is continuously shifting. Mission blue butterflies need to be able to follow the movement of their host plant, but they typically only travel 50 meters (164 feet) from the patch of lupine where they first emerged. Because they are such weak fliers, roads, trails, and dense stands of trees can pose enough of a barrier to prevent them from finding additional lupines, nectar plants, and mates.

Because of these threats, the park has undertaken numerous grassland restoration projects in the last decade. Mission blues appear to be rebounding in some places and spreading into other, recently restored areas.

 

Volunteers helped revitalize the native coastal scrub habitat of Hawk Hill after trees were removed.

GGNPC

Habitat Restoration for Mission Blue Butterflies

Over a number of decades, non-native Monterey pine and cypress trees spread into the grasslands at Hawk Hill. These trees likely arrived as hitchhikers, inadvertently brought in during the construction of military fortifications. The trees became so abundant and dense that they acted as a barrier between areas of lupine on either side of the ridgeline between the Rifle Range and Conzelman Road.

Restoration for mission blue butterflies first began in winter 2011-2012, when six acres of the trees were removed and many areas were replanted with native vegetation. These efforts will allow butterfly populations on either side of the ridge to interact and follow natural shifts in lupines across the landscape. Tree removal also protected the historic military structures from damage caused by root growth.

Restoration continues today, and includes an ongoing focus on native plant reinstatement as well as non-native invasive species control. These invasive species include French broom (Genista monspessulana), jubata grass (Cortaderia jubata), blackwood acacia (Acacia melanoxylon), Australian tea trees (Leptospermum laevigatum), cotoneaster sp., and panic veldt grass (Ehrharta erecta). By eliminating these invasive plants that outcompete the plants that host and feed mission blue butteries, restoration ecologists and volunteers ensure the continued survival of these tiny-but-important pollinators.