The breeding biology of the peruvian tern (Sternula lorata) in Peru

The Peruvian Tern (Sternula lorata) is one of the rarest seabirds that breed on the barren desert plains of Peru and Chile. Unlike the majority of seabirds breeding in this region, Peruvian Terns nest in open areas on the mainland, where they are exposed to attacks by predators, mainly foxes (Pseudalopex spp.). Here, we describe the Peruvian Tern's breeding biology and examine its ecological adaptations to counteract high predation rates from data collected during the 1970s and 1990s at four localities in central-southern Peru: Puerto Viejo (12°34'S), Pampa Lechuzas (13°53'S), Yanyarina (15°26'S) and Mollendo (17°04'S). Egg-laying was asynchronous both within and among breeding groups, spreading from mid October to late January. Modal clutch size was two eggs, which were incubated for 22 d. Weight increment for two chicks during the linear section of the growth curve was 2.27 and 2.54 g/d. A complete body weight growth curve for one chick was fitted to the logistic equation with KL = 0.193 d^-1, A = 50.66 g and ti = 9.9 d. The proportion of nests that hatched at least one chick at Puerto Viejo varied from complete failure in 1971-72 to 80% (N = 6 nests) in 1973-74. Birds did not attempt to breed during El Niño 1972-73. Low nest density (five to seven nests/km²), absence of nest material, camouflage of eggs and chicks, and high mobility of chicks few days after hatching are traits that may decrease nest detection by predators. Conversely, presence of landmarks such as clusters of stones, shell chips, tire tracks and broken glass close to the nest probably enhance nest location by parents in the featureless environment of the desert. Prey remains found in the nests were seven to eight cm Peruvian Silversides (Odonthestes regia regia) and Mote Sculpins (Normanichthys crockeri). The breeding biology and nesting strategies of Peruvian Terns are very similar to the closely-related Damara Tern (Sternula balaenarum) from the coast of South-western Africa and may have evolved to reduce high rates of mammalian predation.