Park), Orange County, had 51 nests in 1968 

 (Davis 1968), 25 in 1969 (Massey 1971), 12 in 

 1970 (Massev 1971) and only 1 or 2 in 1972 

 (Bender 1973, 1974). At this site, fencing was in- 

 stalled and vegetation removed to improve nesting 

 success, but the birds gradually stopped nesting 

 there for unknown reasons, and had not returned 

 as of 1978. In 1969, a colony of 15 pairs was 

 reported from Bair Island, San Mateo County 

 (Anderson 1970). The birds did not use this area 

 in 1971, but were present again from 1972 to 

 1975; 14 active scrapes were located in July 1975 

 (Gill 1977). 



REPRODUCTION 



California least terns are sociable and colonial 

 nesters (Davis 1974). They are easily disturbed on 

 the nest and will take flight for aerial territorial 

 defense. If repeatedly disturbed, they abandon 

 their nests (Hardy 1957, Davis 1974, Wilbur 

 1974). Eggs are small, measuring about 31 by 24 

 mm, and are buff-colored with various brown and 

 purple streaks and specks. One to four are laid, 

 with two to three the most common clutch size 

 (Davis 1968, 1974; Anderson 1970; Swickard 

 1971, 1973; Massey 1972). Eggs are laid late in 

 the morning on consecutive days (Davis 1968, 

 Massey 1971, 1974). 



Nesting starts in mid-May, with most of the 

 nests completed by mid-June (Bent 1921, Davis 

 1968, Swickard 1971, Massey 1974). Late season 

 (July and August) nests may be renests (Wilbur 

 1974). Chambers (1908) believed that terns often 

 reared more than one brood per season, but other 

 authorities do not consider the least tern a multi- 

 ple-nesting species (Wilbur 1974). 



Incubation, which begins with the laying of 

 the first egg, is irregular at first, but become regu- 

 lar once the clutch is completed (Davis 1968, 

 Swickard 1971, Massey 1972). The female does 

 most of the incubating, but both parents partici- 

 pate (Davis 1968, 1974). 



The incubation period varies from 17 to 28 

 days; the normal length is 20 to 25 days (Hagar 

 1937; Hardy 1957; Davis 1968, 1974; Swickard 

 1971; Massey 1972). An incubation period of 14 

 to 16 days given by Bent (1921) apparently is in 

 error. Eggs hatch on consecutive days. Chicks are 

 initially weak, but become strong and mobile by 

 the third day (Davis 1968, 1974). 



In two colonies, hatching success was 80% to 



90%, and fledging rates varied betwen 1 1% and 

 50% (Swickard 1971, Massey 1972). Infertility 

 appears to be a minor cause of egg failure (Wilbur 

 1974). Predation pressures appear to be high on 

 both eggs and fledgings. Domestic predators 

 (house cats and dogs) and Norway rats {Rattus 

 norvegicus) are often implicated (Chambers 1908; 

 Edward 1919; Craig 1971; Swickard 1971, 1973; 

 Pentis 1972; Atwood et al. 1977). 



In the past, high tides caused heavy losses of 

 California least tern eggs (Shepardson 1909, 

 Sechrist 1915). Now few colonies are found in 

 areas where tides are a problem. However, in areas 

 with soil less permeable than beach sands, sum- 

 mer rains can cause serious nest losses. Swickard 

 (1971) noted that birds nesting on salt flats had 

 only 43% hatching success after flooding from 

 heavy rains, while on adjacent beach sands, rain 

 water percolated through the nests and there was 

 a 90% hatching success. 



MANAGEMENT AND CONSERVATION 



The least tern can tolerate some kinds of 

 human activities; they have nested successfully 

 between runways on military air fields (Atwood 

 et al. 1977), in a small fenced enclosure on a pub- 

 lic beach (Anon 1970, Massey 1972), beside a 

 shopping center parking lot (Atwood et al. 1977), 

 and on man-made fill alongside coastal lagoons 

 and estuaries (Massey 1972, Pentis 1972). How- 

 ever, use of any site depends on a nearby body of 

 water containing abundant small fishes and on 

 protection from harassment and predation (Wil- 

 bur 1974). Fencing, posting and educational 

 displays, and limited predator control provide 

 protection for nesting birds (Craig 1971; Massey 

 1972; Bender 1973, 1974; Atwood et al. 1977). 

 Suitable feeding areas appear to be in critically 

 short supply. Protecting those few that remain 

 and restoring others that no longer support ade- 

 quate fish populations because of reduced tidal 

 flow or pollution may be the most significant 

 management plan for the tern (Wilbur 1974). 



Since least terns require open nesting areas, 

 natural succession tends to eliminate suitable 

 nesting areas, particularly on man-made sites. 

 Vegetation removal is advocated to encourage the 

 continued use of those nesting beaches under- 

 going succession. 



At Bair Island, the substrate is sandy loam 

 which, when wet, sticks to tern eggs. In 1977, 



