Ectoparasite Effects on Nestling European Storm-Petrels

Abstract

-A colony of European Storm-petrels (Hydrobates pelagicus) on Benidorm Island was studied during 1996 breeding season. We experimentally tested whether ectoparasites affected growth and health of nestling stormpetrels. Four species of ectoparasites were found on nestlings; the most common were a dermanyssid mite and the flea Xenopsylla gratiosa. We manipulated ectoparasite loads on chicks by assigning them to one of three treatments: fumigated with insecticide, ectoparasite addition, or control. Nestlings in the fumigated group gained mass at a higher rate than those in the control group, and nestlings from the parasite addition treatment gained mass at the lowest rate. Because slower mass gain may delay fledging or reduce survival, ectoparasites may be an important selective force on European Storm-petrels. Received 31 March 1999, accepted 17 April 1999. Key-words.-Ectoparasites, fleas, growth, hematocrit, mites, European Storm Petrel, Hydrobates pelagicus. Waterbirds 22(2): 297-301, 1999 Research over the last 20 years has demonstrated the influence of parasites on many aspects of host life histories (Price 1980; Loye and Zuk 1991; Moller 1997). In birds, many of the studies have focused on parasitism and host reproductive success (Loye and Zuk 1991; Moller 1990; Merino et al. 1996). Parasitism may affect reproduction of hosts; nestlings supporting high numbers of parasites may grow slower and suffer higher mortality rates (reviewed in Moller et al. 1990; Lehman 1993). In addition, parasitism can be an important cost of coloniality in birds, because high nest densities can enhance transmission of ectoparasites and diseases (Brown and Brown 1986; Shields and Crook 1987). Several works report high costs of parasitism, mainly due to nestling mortality and nest abandonment of colonial seabirds (Converse et al. 1975; King et al. 1977; Feare et al. 1994). In addition, in many underground-nesting seabirds, chicks frequently move between neighboring nests, interacting with other chicks or adults (Winkler and Walters 1983) and increasing the probabilities of horizontal transmission of ectoparasites, a factor related to high parasite virulence (Frank 1996). The European Storm-petrel (Hydrobates pelagicus) is an endangered colonially-nesting seabird that breeds on islands along European coastlines. It is a small, nocturnal petrel that nests in crevices. It raises one chick per breeding attempt; fledging occurs about 63 days after hatching (Davis 1957). Although young chicks tend to remain at their nest-sites, older chicks progressively increase their activity and movements out of the nest (Minguez 1997). During routine field work, a high infestation by ectoparasites was observed on nestlings at two colonies on Benidorm Island (38'30'N, 0008'E), off the Mediterranean coast of Spain, where about 400 pairs of European Storm-petrel breed (Minguez 1994). The aims of this study were to identify the ectoparasite fauna infesting storm-petrels and to investigate whether parasites imposed costs to growing chicks in terms of development rate (wing length and mass attained, increase in growth measures and different rates of growth during experimental treatment). In addition, we checked for differences in the hematocrit value, a measure that may be related to ectoparasite effects and nestling health (i.e. anemia).