Full-text - Norsk entomologisk forening

highest prevalence on adult birds on puffins andthe lowest on kittiwakes. The prevalence on youngbirds was highest for kittiwakes with guillemotsfollowing close behind. The greatest numberticks per individual were found on a kittiwakefledgling. In general, young birds hostedmany more ticks than adults, with the exceptionof puffins.Relatively few ticks were found on youngpuffins. This may be an indication that the microclimatein puffin burrows is unsuitable for I.uriae, or else that most of the ticks that werepresent in the burrows fed on adults during thenesting and brooding periods. The latter seemsto provide the best explanation since relativelymany ticks, including males, were collectedfrom puffin burrows, thus indicating that theconditions are suitable for the development ofticks.When one considers the numbers of nestingpuffins, guillemots and kittiwakes 000.000,3.000 and 90.000 pairs respectively) on the islandsof R0st in relation to the number of tickscollected, an overall evaluation of the data indicatesthat puffins hosts a much greater proportionof the tick population than the other twobird species.A feature which is common for all of the birdspecies which host I. uriae is that they all formlarge persistent breeding colonies with a highnest density. Such conditions enable I. uriae toreadily find new host individuals. I. uriae is anactive tick, and apparently searches for a hostrather than waits passively until one passes.Another factor which is important for breedingand survival of I. uriae, is the presence of welldrainedand relatively dry habitats near the nestsof the hosts. This provides the ticks with a microhabitatsuitable for winter survival, moultingand egg laying. We agree with the conclusionsof Murray & Vestjens (\967) that I. uriae is nothost specific and that its distribution is principallydue to factors which influence the survivalof the free-living stages of its life-cycle. breedingand moulting behaviour ofthe hosts may also beinvolved in its distribution determination.Both visual observations and collections ofticks on the ground in the puffin colonies gavethe impression that the spatial distribution of theticks was variable and that this was not relatedto the population density of the puffins. It is likelythat a variable distribution on the groundwill result to variations in the number of ticksper bird.A number of factors are involved in determiningthe spatial distribution of ticks: density ofbird host, topography. microclimate, soil conditions,dispersion and aggregation (by pheromons?)of the ticks themselves, or with the aidof birds, and by fully engorged ticks fallingdown the cliffs. Temporal variation in the tickpopulation can be influenced by climatic conditions,shifting of breeding period, the productionand survival of young birds, and a number ofotherfactors (Murray & Vestjens 1967, Karpovich1973, Kelly 1980, 1982, Lid 1981, Myrberget1981).The numbers of ticks which can be obtainedby using our collection methods depend greatlyon the weather and season of the year. The resultsof flagging in the beginning of May vividlyillustrate this point. Also, under certain conditionslarge numbers of non nesting birds can visitland for a short period and thus (Myrberget1959) influence the results of the investigation.This occurred on July 25, 1979.We regard the quantitative results of the pre- ,sent investigation as reflections of the methodsemployed and the prevailing cdnditions. Theecological conditions in seabird colonies arequite complex and variable, and only certainparts of the bird cliffs were included in our studies.We did not, for example, investigate thesteepest parts of the bird cliffs. Consequently, •the general conclusions from this study must beseen in the light of the limitations imposed. Variationsin natural phenomena probably constituteimportant factors underlying many of thedescrepancies encountered in descriptions of theecology of I. uriae.The observed seasonal abundance of I. uriaein Norway corresponds to the descriptions fromMurmansk region and Newfoundland. We observedthat I. uriae survived winter as eggs, larvaeand nymphs (unfed and engorged) and asadults (unfed only).It appears as though all adults and the majorityof nymphs overwinter in the unfed state. Inlate September 1973, we estimated that 22 % ofthe nymphs which had fed during the summer,still were engorged, and most likely would passthe winter in that state. Based on the collectionof ticks in early May 1978, we estimated that13 % of the nymphs which fed the previousyear, had passed the winter in engorged state.Karpovich (1973) observed mass death of engorgedticks in a cold winter and concluded thatonly eggs and unfed ticks are well adapted tooverwintering.Nymphs become active earlier in the springthan the adults. This may indicate that a part ofthe population overwinters in tussocks and104