{Gambusia affinis) (Swickard 1971;Massey 1972, 

 1974; CLTRT in prep). Other subspecies occa- 

 sionally feed on Crustacea, molluscs, sand eels 

 (Ammodytes), annelid worms, and insects 

 (Tompkins 1959). 



SHELTER REQUIREMENTS 



At first the young are weak and helpless. 

 Adults brood chicks continuously the first day. 

 By the second day, chicks make short walking 

 trips from the nest. From the third day on, they 

 become more active and are increasingly mobile 

 (CLTRT in prep.) 



NESTING OR BEDDING: 



Nests are simple, shallow depressions in sand, 

 dirt or gravel, usually without twigs or other 

 materials. Bent (1921) states that on beaches 

 where there are shells, the birds may encircle their 

 scrapes with them. Likewise, Swickard (1971, 

 1973) reported finding one nest, located on flat 

 ground, that was completely lined with small 

 twigs; Massey (1974) reported that nearly 20% of 

 the nests she studied were partly or completely 

 shell-lined. 



In sand, the bird scoops out the nest depres- 

 sion (Davis 1968, 1974; Massey 1971, 1974;Swi- 

 ckad 1971). But in hard soil, such as dried mud or 

 fill, the nest can be any kind of natural or artifi- 

 cial depression, including a dried boot track (Swi- 

 ckard 1971). 



Scrapes are circular, about 20 mm deep and 

 120 mm in diameter (Hardy 1957). Temporary 

 scrapes are used for brooding when chicks begin 

 to wander (Hardy 1957). 



Least terns are colonial, but usually do not 

 form dense concentrations (Wilbur 1974). The 

 distance between nests is 3 to 5 m or more (Wolk 

 1954; Hardy 1957; Massey 1971, 1974). Nesting 

 densities may be as low as 3 to 7 per ha (Swickard 

 1971, 1973), although they are often greater; 145 

 pairs nested on about 0.75 ha at FAA Island in 

 Mission Bay, San Diego County, California. 



RITUAL REQUIREMENTS 



Nesting beaches are usually used as a parading 

 ground during courtship (Hardy 1957, Wilbur 

 1974). 



OTHER CRITICAL ENVIRONMENTAL 

 REQUIREMENTS 



Open expanses free from human disturbance 

 are necessary for courtship, resting, and nesting; 

 adjacent unpolluted lagoons or estuaries are 

 needed for feeding (Longhurst 1969, Craig 1971, 

 Wilbur 1974). 



POPULATION NUMBERS AND TRENDS 



Thousands of terns once nested on the beaches 

 and near the estuaries of the Pacific Coast of 

 North America from Monterey Bay south to cen- 

 tral Baja California. These flocks have dwindled 

 rapidly in the last century. In 1970, the popula- 

 tion in California was estimated at less than 300 

 pairs, scattered over 15 nesting colonies (Craig 

 1971), but this study was not made in the nesting 

 season and did not attempt to obtain precise 

 population data. The California Department of 

 Fish and Game has since conducted annual cen- 

 suses. In 1973, initial surveys estimated a popula- 

 tion size of 624 pairs, with nesting activity at 19 

 sites (Bender 1973). The 1974 surveys estimated 

 the breeding population at 582 pairs. Breeding 

 activity was recorded at 20 sites, but nesting 

 occurred at only 16 of them (Bender 1974). The 

 estimated breeding population was 600 pairs in 

 1975 and 664 pairs in 1976 (Atwood et al. 1977). 

 In 1977, 775 breeding pairs were located at 

 29 colony sites, but 9 colonies were abandoned or 

 had poor nesting success because of human distur- 

 bance, predation, or flooding (Atwood et al. 

 1977). This was the largest breeding population 

 since the surveys began, but the greater numbers 

 found are due in part to increased survey staff 

 and more accurate survey methods (Atwood et al. 

 1977). 



The breeding population of the California 

 least tern is difficult to assess for several reasons. 

 Birds may shift breeding sites from year to year, 

 breeding dates may not be uniform, and age at 

 first reproduction and longevity are unknown. 

 Less standardized and concentrated censusing in 

 the past no doubt missed nesting birds at some 

 locations, and some censuses were too late or too 

 early to find breeding birds. 



Local perturbations compound the difficul- 

 ty in estimating population trends. A colony at 

 Huntington Beach (Sunset Aquatic Regional 



