RANGE 



The historical breeding range of the California 

 least tern extended along the California coast 

 from Moss Landing, Monterey County, to San 

 Jose del Cabo in southern Baja California (Daw- 

 son 1924, Grinnell 1928, Grinnell and Miller 

 1944, A.O.U. 1957). Some least terns have nested 

 in a number of locations farther north; between 

 1939 and 1954, they nested at the mouth of the 

 Pajaro River, Santa Cruz County (Pray 1954, 

 Wilbur 1974), and nesting near San Francisco Bay 

 in Alameda, Alameda County, was confirmed in 

 1967 (Chandik and Baldridge 1967). There are 

 numerous spring and summer records for this area 

 (Grinnell and Wythe 1927, Allen 1934, Sibley 

 1952, DeBenedictis and Chase 1963, Chase and 

 Paxton 1965). Wilbur (1974) suggests that 

 nestmg may have occurred here previously. In 

 south San Francisco Bay, 60 were counted on 1 

 Sept 1968, and a breeding colony of 30 pairs was 

 established on Bay Farm Island, Alameda County, 

 in 1969 (Gill 1977). A colony of 15 pairs was also 

 reported in 1969 from Bair Island, San Mateo 

 County (Anderson 1970). The nesting range has 

 apparently always been widely discontinuous, 

 with the majority of birds nesting in southern 

 California from southern Santa Barbara County 

 south through San Diego County (Wilbur 1974). 

 Known nesting sites in Baja California are Scam- 

 mons Lagoon (Bancroft 1927, Grinnell 1928), 

 San Jose del Cabo (Lamb 1927, Grinnell 1928), 

 Ensenada (Bahia Todos Santos), and Baliia de San 

 Quintin (Massey 1977). 



The California least tern is migratory, usually 

 arriving at its breeding area during the last week 

 of April and departing again in August (Davis 

 1968, 1974; Massey 1971; Swickard 1971, 1973), 

 although terns have been recorded as early as 1 3 

 March and as late as 31 October (Sibley 1952, 

 Wilbur 1974). 



There are six records north of San Francisco 

 Bay and four records of single birds seen at Hum- 

 boldt Bay, Humboldt County; two specimens 

 were collected at Fort Steven, Clatsop County, 

 Oregon (DeSante et al. 1972, CLTRT, in prep.) 

 Migrating least terns have also been recorded from 

 the Colorado River valley (Grater 1939, Phillips 

 et al. 1964) and at the Salton Sea, Imperial Coun- 

 ty (McCaskie and Cardiff 1965, McCaskie 1971). 



The winter distribution of the California least 

 tern is unknown. Least terns in Guatemala 



(Griscom 1932) and Veracruz (Warner and Mengel 

 1951) have been identified as members of the 

 subspecies browni. California least terns are 

 thought to migrate to Peru, but Murphy (1936) 

 doubts this. Recent efforts to find them in Peru 

 have been unsuccessful. 



RANGE MAP 



Known nesting locations for the California 

 least tern are shown on the accompanying map 

 (from Wilbur 1974). 



STATES/COUNTIES: 



California: Alameda, Imperial, Los Angeles, 

 Monterey, Orange, San Diego, San 

 Mateo, Santa Barbara, Santa Cruz, 

 Ventura. 



Mexico: Locations of breeding colonies in Baja 

 California south of Bahia de San 

 Quintin are unknown. 



HABITAT 



Nesting colonies require undisturbed flat areas 

 with loose substrate, such as sandy upper sea 

 beaches or open expanses of fill-dirt or dried mud 

 characterized by little or no vegetation. For forag- 

 ing, they need adjacent open ocean, surf-line, 

 estuary or lagoon with a good supply of small fish 

 (Grinnell and Miller 1944; Craig 1971; Massey 

 1971; Swickard 1971, 1973; Wilbur 1974). 



FOOD AND FORAGING BEHAVIOR 



Least terns often feed in small loose groups of 

 2 to 10 birds. While fishing, they hover above the 

 water. If prey is sighted, the bird quickly plunges 

 to the surface, usually breaking its fall just before 

 reaching the water so it is only partially sub- 

 merged instead of diving beneath the surface. 

 Often, a series of short plunges and repeated hov- 

 erings will occur before the actual dive, which is 

 then usually made from only a few centimeters 

 above the water (Bent 1921, Hardy 1957). 



They have not been seen eating anything but 

 fish, including northern anchovy {Engraulis mor- 

 dax), shiner perch {Cymanogaster aggregata), 

 anchovy [Anchoa compressa), topsmelt (Athertn- 

 ops affinis), killifish {Fundulus parvtpinnts) , ']a.ck- 

 smelt [Atherinopsis calif orniensis) , California 

 grunion [Leuresthes tenuis) and mosquito fish 



