NESTING SUCCESS OF CALIFORNIA LEAST TERNS 
ravens). At other colonies predators often include introduced fauna (Burger 
1984, Martinez 2006). The Black-crowned Night-Heron ( Nycticorax nyc- 
ticorax) is a major predator of Least Tern eggs and chicks at some colonies 
(Brunton 1999). Though the herons breed at Guerrero Negro (Gutierrez- 
Aguilar pers. obs.). the tern colony is away from areas they frequent. 
That clutch size remained constant through the season suggests that at 
Guerrero Negro egg laying was not limited by food, at least in the single 
year of our study. Clutch size is known to be affected by food availability in 
various species of Laridae (Harris and Plumb 1965). 
Hatching success at Guerrero Negro fell between the values of 57% and 
90% reported for protected colonies of this species (Swickard 1974, Massey 
and Atwood 1981, respectively). Even the much lower hatching success 
later in the season (16%) was higher than values reported for some unpro- 
tected colonies (between 4% and 12%, Zuria and Mellink 2002, Ibarra and 
Carmona 1998, respectively). An exception to the lower values found in 
colonies without active protection is at Punta Banda, where hatching success 
values of almost 60% (Palacios 1992, Zuria and Mellink 2002) are linked to 
a minimal effect of the tides. 
As at many colonies, the principal problem for the Least Tern at Guerrero 
Negro was predation, in this case by coyotes. Coyote predation could be 
avoided by fencing the colony to prevent access. 
The Guerrero Negro saltworks, although carefully managed for salt 
production, is as undisturbed as any segment of the Baja California coast. 
The colony’s high success rates is an example of human development not 
conflicting with conservation. The Least Tern colony at Guerrero Negro 
having success similarly to that of actively protected colonies elsewhere on 
the peninsula indicates that with minimal effort the saltworks can contribute 
to the conservation of these birds. 
ACKNOWLEDGMENTS 
We acknowledge A. M. Cisneros and N. Atkins for their invaluable help in the writ- 
ing of the manuscript and to the authorities of Exportadora de Sal for their support, 
including unrestricted access to their installation. 
LITERATURE CITED 
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Brunton, D. H. 1999. “Optimal” colony size for Least Terns: An intercolony study of 
opposing selective pressures by predators. Condor 101:607-615. 
Burger, J. 1984. Colony stability in Least Terns. Condor 86:61-67. 
Carmona, R., and Danemann, G. D. 1998. Distribution espaciotemporal de aves 
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