eWestern BirdsThe Quarterly Journal of Western Field Ornithologists
Vol. 45, No. 3
Western Field Ornithologists
Reuse of Nest Sites by Pelagic Cormorants in Northern California
Ellen S. Martinsen and Joseph J. Schall
ABSTRACT: We photographed nests of Pelagic Cormorants (Phalacrocorax pelagicus) on cliff ledges at two colonies in Mendocino and Sonoma counties, California, from 1986 to 1996. In 135 comparisons of the positions of nests in different years, we found that 92% of the nests shifted by <25 cm (approximate diameter of a Pelagic Cormorant nest), and in 24% of comparisons the shift was <5 cm. Some nests were placed within a few centimeters of previous sites for as long as nine years. The rate of reuse of nest sites was high on both small ledges and on large shelves where the nest could have readily been shifted. At sites where substantial rock substrate sloughed off the cliff face in the previous year, nests were placed precisely at former sites. This high rate of nest reuse is striking because many apparently suitable sites on these cliffs remain unused.