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 coming back to the site. One of the first invertebrates to be protected under the Endangered Species Act, this small butterfly is an important component of area grasslands. Though they are in the area year-round, they're most noticeable for only 6-8 weeks of the year when the adults can be seen flying about. Amazingly, these butterflies emerge from a 51-week hibernation and metamorphosis to travel to locate their food plants, mate, and die within a single week.
Mission blue numbers took a plummet in the mid-90s after a fungal pathogen attacked their host lupines. But in the last decade the park has undertaken a number of grassland restoration projects and butterflies appear to be rebounding in some places and spreading into other, recently restored areas.
Mission blues lay their eggs on three species of lupine that are the sole food source for their caterpillars. These lupines grow scattered among fields of coastal prairie and scrub, but because they thrive at recently disturbed sites, good lupine habitat is continuously shifting. Mission blue butterflies need to be able to follow this natural host plant movement, 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.