A comparitive study of the ischnoceran Mallophaga of Wilson's Petrel Oceanites oceanicus and British Storm Petrel Hydrobates pelagicus

The frequency distribution of an elongate feather louse Philoceanus robertsi found on the Wilson's Storm Petrel Oceanites oceanicus conforms well with a negative binomial model. Its infestation density and frequency distribution are similar to those previously described for another elongate louse Halipeurus pelagicus found on the Storm Petrel Hydrobates pelagicus. An anaysis of the population structures of the lice reveals that both species have highest reproductive rates during the breeding season of the host, but both structures become dominated by adults, suggesting an ageing and declining process, towards the end of the hosts' breeding season. Philoceanus robertsi is also found on the Storm Petrel, but at a much lower density. Its reproductive cycle on this host appears to be in synchrony with that on the population on Wilson's Petrels. Explanations in terms of niche differentiation are offered.