Activity patterns and effect of ticks on growth and survival of tropical Roseate Tern nestlings

Patterns of abundance of the seabird tick Amblyomna loculosum and their eff ects on Roseate Tern (Sterna dougallii) nestling growth, fledging age, and survival are described on Aride Island, Seychelles, in 1997-1999. Female ti cks attached to nestlings from 4 to 14 days (to engorge) whereas male ticks attached for 1-3 days. The linear growth rate of birds carrying female tic ks (0.24 g/day) was significantly different from that of nonparasitized nes tlings of the same age and similar (or even lower) hatching weight (4.07 g/ day). Parasitized nestlings that fledged did so 5.2 days later than nonpara sitized nestlings of Similar age. Only 37.5% of the nestlings infested with female ticks fledged compared with 83.3% of the noninfested nestlings. Dur ing the successful 1998 breeding season, around 100 nestlings died from tic k infestation (24.3% of the nestling deaths). Ticks appeared to accelerate nestling mortality during periods of food shortage. Despite an annual diffe rence of two weeks in the timing of breeding of the Roseate Terns between 1 997 and 1998, adult ticks parasitized nestlings in July, with an infestatio n peak occurring between 8-12 July in both years. However, in 1997, nestlin gs were parasitized at a younger age, suggesting that ticks (nymph stage) m ust attach to Roseate Tern adults as soon as they make a nest scrape (usual ly in May). Ironically, the frequent breeding failures of the Roseate Terns will result in lower infestation levels in subsequent years, which will be nefit the birds.