being reduced by erosion from the bay waters, and also by the encroachment of invasive plants such as ice plant and marguerite daisies. The terns face strong competition at Brooks Island from a growing population of California gulls. The gulls "compete with the terns for nesting sites, steal fish from them, take their eggs, even chicks if they're small enough". Other bird species Many other species of birds, both common and rare, use Brooks Island. The north-east shore hosts a large seasonal colony of herons and egrets. To the immediate west, Bird Island is a nesting site for Canada geese (Branta canadensis), for which it was the first breeding location in the Bay Area, black oystercatchers (Haematopus bachmani), and western gulls (Larus occidentalis). Insects The persistence of many of the East Bay's native plants on Brooks Island provides rich habitat for insects. Ten percent of the 220 moth and butterfly species recorded on Brooks Island by UC Berkeley entomologist Jerry Powell and colleagues during the period 1993–1997 were either unknown in the San Francisco Bay region or unrecorded for 50 to 100 years. These included the Mexican tiger moth, not previously thought to occur in the Bay Area. Flora Because of its limited history of human exploitation, plant communities that are rare elsewhere in the East Bay remain on Brooks Island. While Brooks Island has a variety of plant communities, the most common are coastal grassland and northern coastal scrub. It has been described as a "showcase for coastal grassland, which occurs on the island in a relatively undisturbed state", covering about of mostly flatter terrain. These grassland areas are relatively free of exotic Mediterranean grasses and instead are dominated by needlegrasses (purple needlegrass (Nassella pulchra) and otherNassella spp.), ryegrasses (Lolium spp.) and fescues (Festuca spp.). Among the grasses are native wildflowers such as blue dicks (Dipterostemon capitatus), soap plant (Chlorogalum parviflorum) and checker mallow (Sidalcea malviflora). Another notable relict population is the seaside woolly sunflower which is present in only a few other East Bay locations. Overall, the diverse flora includes about 150 species of flowering plants, of which 92 are native species. There are very few trees on the island: on the northeast side of the island near the shell middens are two clusters of old California buckeyes (Aesculus californica), a single red willow (Salix laevigata) and some blue elderberry (Sambucus mexicana). Around the two ponds in the