The Ecology of Tick Parasitism on Densely Nesting Peruvian Seabirds

Densely nesting Guanay Cormorants (Phalacrocorax bougainvillii), Peruvian Booby (Sula variegata), and Peruvian Brown Pelican (Pelecanus occidentalis thagus) deserted eggs and young in response to high densities of argasid ticks (Ornithodoros amblus). Alternative causes of desertion such as human disturbance, predation, disease, heat, and food shortage did not fit the evidence. Tick predators were less effective at controlling ticks than were frequent human harvestings of guano. A review of the avian and medical entomological literature indicates that ticks and other ectoparasites may be strong determinants of nesting success and of nest structure and duration of use.