Ring-billed Gull Larus delawarensis Ord       Field Guide IDs: NG- 198; G-146; PE-86; PW-pl 33; AE-pl 38; AW-pl 24; AM(II)-54 Nest Location Nest Type Eggs & Mating System Dev. & Parental Care Primary & 2ndary Diet.. Foraging Strategy MF I: 21 DAYS SEMIPRECOCIAL MF 2-4 (1-7) MONOG (POLYGYN) F: ? DAYS MF HIGH DIVES SURFACE DIPS BREEDING: Rocky islets or isolated coasts, occ marshes. 1 brood. DISPLAYS: Courting pair face each other, one lowers head, flattens crown, elongates; pair then alternately circle several times, raise heads and call. Female oft assumes "submissive" hunched posture. NEST: Open or concealed among rocks on matted veg; of grass, forbs, rubbish, etc., lined with fine grass, feathers. Occ simple lined scrape. EGGS: Buffy white, marked with browns. 2.3" (59 mm). DIET: Fish, insects, worms, rodents, bird eggs, offal; in winter, much garbage. Chicks' diet parallels adults' diet. CONSERVATION: Winters s to s Mexico, Bahamas, and Greater Antilles. Increased in response to food provided by garbage dumps. NOTES: Colonial, occ assoc with California Gulls, terns, ducks, cormorants. Polygyny and females associating without males are rare (less than 1% of nests in large colonies) and account for all nests with >4 eggs. Mate change oft with neighbor of previous year, result of esp strong nest site tenacity. Young remain in nest on day of hatching. Frequent pirate. Adult plumage attained in third year. STANFORD. NOTES: Generally an uncommon visitor to campus from fall through spring. Usually seen foraging on playfields or at the Oval, where it may be locally common at times (especially when feeding on earthworms after rains). Also forages and bathes at Lagunita ESSAYS: Parent-Chick Recognition; Vocal Development; Gull Development; Site Tenacity; Coloniality; Gulls and Predators. REFERENCES: Boersma and Ryder, 1983; Conover, 1984; Southern et al., 1985.