JOURNAL OF AVIAN BIOLOGY 28: 150-156. Copenhagen 1997 Patterns in the distribution of avian lice (Phthiraptera: Amblycera, Ischnocera) Jozsef Rkkasi, Lajos Rozsa and Botond J. Kiss Rekasi, J., Rozsa, L. and Kiss, B. J. 1997. Patterns in the distribution of avian lice (Phthiraptera: Amblycera, Ischnocera). - J. Avian Biol. 28: 150-156. The frequency distributions of 15 species of avian lice among individuals within host populations are described and 12 previously described distributions are reviewed. All of these distributions were aggregated, but some of them do not conform to the negative binomial model (4 at P < 0.05 out of the 25 examined). Distribution measures (prevalence, mean and variance of louse subpopulations. the exponent k of the negative binomial distribution. and the index of d~screpancy) 01' lice of colonial birds are compared to those of territorial ones. Minimum ;ampie size requirement is calculated for each case study. Louse subpopulation size and variance do not correlate with host social system, however, residuals from the log mean-log variance regression do. Lice of territorial hosts tend to form more variable subpopulations than those predicted by the regression curve, while those of colonial birds tend to form less variable subpopulations. Prevalence and k are higher, while the index of discrepancy is lower, for the distributions of lice of colonial hosts, indicating less aggregated louse distributions compared to those of territorial host species. J. Rtkasi, Benedictiner School, H-9090 Pannonhalma, Hungary. L. Rozsa (correspon- dence), Department of Parasitology and Zoology, University of Veterinary Science, H-1400 Budapest, P.O. Box 2, Hungary. E-mail: lrozsa@ns.univet.hu. B. J. Kiss, 8800 Tulcea, Op. 4, P.O. Box 13, Romania. An aggregated distribution is a general feature of the Unlike lice, these arthropods have free-ranging invasive occurrence o f parasites within their host populations: forms capable o f actively searching for new host indi- many hosts have few i f any parasites, while a few have viduals. a lot o f them. This phenomenon is also referred to as a In contrast, avian lice are contagious ectoparasites as contagious or clumped distribution. Its causes and con- their transmission is highly dependent on direct body- sequences have been studied extensively in many taxa to-body contacts among hosts. In a comparison be- o f parasites. Following Crofton (1971) the negative tween lice o f a territorial versus a colonial corvid binomial distribution is widely used as a mathematical species, louse subpopulations exhibited similar means, model to describe this pattern. Here we provide data on but tended to be more prevalent and less aggregated on 15 new and 12 previously published case studies de- the colonial host, suggesting that colonial breeding may scribing the distribution patterns o f avian lice (Phthi- facilitate horizontal transmission o f avian lice (Rozsa et raptera: Amblycera, Ischnocera) within their host al. 1996). Feather mites, another group o f contagious populations. ectoparasites, also exhibited a higher prevalence on Host sociality is known to affect host-parasite inter- colonial bird species than on territorial ones (Poulin actions. Case studies on avian ectoparasites, including 1991). nest-dwelling mites, ticks, bugs, fleas and flies, indicate To investigate whether the effect of host social be- that an increased level o f ectoparasitism may be a cost haviour can also be detected in the present data set we o f social life (Brown and Brown 1986, Marller 1987, compare the distribution measures of the lice of colo- Shields and Crook 1987, Duffy 1991, Chapman and nial hosts (12 distributions) to those o f territorial ones George 1991, Loye and Carroll 1991, Poiani 1992). (1 5 distributions). 0 JOURNAL OF AVIAN BIOLOGY JOURNAL OF AVIAN BIOLOGY 28:2 (1997)