Ardeola 47(2), 2000, 269-271 LOW PREVALENCE OF INFECTION BY HAEMOPARASITES IN CETTI’S WARBLERS CETTIA CETTI FROM CENTRAL SPAIN BAJA PREVALENCIA DE INFECCIÓN POR HEMOPARÁSITOS EN RUISEÑORES BASTARDOS CETTIA CETTI DE ESPAÑA CENTRAL S. MERINO*, J. SEOANE**, J. DE LA PUENTE*** & A. BERMEJO*** In spite of considerable effort devoted du- Warblers (see Peirce, 1981; Bennett et al., ring the last two decades to understand the dis- 1982; Bishop & Bennett, 1992). Here we stu- tribution and impact of blood parasites on their died the prevalence, age distribution of infected bird hosts, the species, prevalence and effects individuals and time of infection by blood pa- of blood parasites infecting many birds are still rasites in Cetti´s Warblers Cettia cetti. largely unknown (Peirce, 1981; Bennett et al., To capture birds, mist nets were operated 1982; Bishop & Bennett, 1992; Merino et al., once a week between December 1996 and De- 2000). Knowing the presence and impact of cember 1997. Ten nets of 12 meters and one of blood parasites may be important for managing 18 meters long were used in an extensive reed- wild populations and for understanding parasi- bed along the Jarama River near San Martín de te specificity and distribution, as well as inters- la Vega (Madrid, Central Spain; 40° 19´ N, 3° pecific interactions. In addition, pathogens may 32´ W) during a long term monitoring project. restrict the population range of their hosts and All birds were captured within a period of six influence the competition between species (Fre- hours after sunrise, ringed with numbered alu- eland, 1983). minium rings and sexed and aged according to Cetti’s Warblers live in marshy areas from Svensson (1996) and Gargallo (1997). A drop Western Europe to Pakistan (Cramp, 1992). of blood was obtained from the brachial vein Their secretive behaviour and mimetic dull co- and immediately smeared and air dried. Smears lour allows them to go unnoticed were it not were fixed with absolute ethanol and stained because of their loud song. Males are larger with Giemsa (1/10 v/v with phosphate buffer than females, and polygynous males usually at pH 7.2) for 45 min. Samples were scanned in pair with one to three females, which lay one or search of blood parasites as described in Merino two clutches per year (Bibby, 1982; Bibby & & Potti (1995) and Merino et al. (1997). In Thomas, 1984). The breeding period lasts from brief, half a smear was scanned at 200X in se- March to July and males appear to maintain te- arch of extraerythrocytic parasites and 20 fields rritories year-round. Although plant food is an were scanned at 400X. Oil immersion magnifi- important dietary component in Spain, the spe- cation was used for identification of parasites. cies is mainly insectivorous (Molina et al., The number of parasites per 2000 erythrocytes 1998). was used as an index of the intensity of infec- Cettia appear to be a bird genus with low tion (Godfrey et al., 1987). prevalence of infection by haematozoa. Thirte- One hundred and twenty six individuals en species in the genus have been described were captured, 32 of them were recaptured (Howard & Moore, 1991) and six of them have once, seven were recaptured twice and one was previously been sampled for haematozoa, with captured five times. Some individuals were in negative results with the exception of Cetti´s the area between September and March (win- * Museo Nacional de Ciencias Naturales, CSIC, C/. José Gutiérrez Abascal, 2, E-28045 Madrid, Spain. E-mail: [email protected] . Author for correspondence. ** Departamento de Ecología, Universidad Autónoma de Madrid. E-28049 Madrid. Spain. Present ad- dress: Estación Biológica de Doñana, Avda. María Luisa s/n, Pabellón del Perú. E-41013 Sevilla. Spain. E- mail: [email protected] *** Departamento de Ecología, Universidad Autónoma de Madrid. E-28049 Madrid. Spain. E-mail: [email protected] 270 MERINO, S., SEOANE, J., DE LA PUENTE, J. & BERMEJO, A. ter) and others between March and September cords of infection by Plasmodium and Atoxo- (breeding and post-breeding). The highest num- plasma in Cettia cetti . ber of captures were in September when winter The situation in Cetti´s Warblers resemble and post-breeding dispersing populations mix that in Choughs Pyrrhocorax pyrrhocorax from in the area. a nearby area where Plasmodium appears in Only four birds (3.2%) were infected, three low numbers and apparently without severe ef- of them by a Plasmodium species of the subge- fects on hosts (Blanco et al., 1997). However, nus Haemamoeba and one by Atoxoplasma sp. the presence of low intensity infections by Representative slides are deposited in the Mu- Plasmodium in young, probably naive birds, seo Nacional de Ciencias Naturales, Madrid, may be also indicative of high pathogenicity Spain (access numbers: 35.02/1 and 35.02/2). causing death of birds suffering from high in- The Plasmodium species may be one in the tensities of infection (Warner, 1968). The diffi- group comprising P. relictum, P. subpraecox culty in capturing individuals with signs of ill- and P. giovannolai, which cannot be separated ness, may obscure the effects of this parasite. In based only on blood smears and host data (Grei- addition, the data presented here may indicate ner et al., 1975). P. subpraecox is probably that this parasite is opportunistic, infecting low restricted to owls; the other two species have numbers of birds in the area, and probably been previously recorded for Sylviinae, P. re- more common than previously supposed (Blan- lictum being the most frequent (Bennett et al., co et al., 1997). As this parasite is not highly 1993a). The three individuals infected with host-specific, its population may be maintai- Plasmodium were captured in July, August ned in various species, some of which may be (males) and October (female), respectively. The only rarely infected. individual infected in July had a very low in- Atoxoplasma, previously Lankesterella (Le- tensity of infection with less than 0.1 parasites vine, 1982), is a poorly known parasite genus, per 2000 erythrocytes. That bird was recaptured usually transmitted by vector swallowing and 15 days later and the infection was almost ab- not by its bite as is the case for Plasmodium sent with only some trophozoites present in the species. A considerable part of the diet of Cet- smear. The male found infected in August sho- ti’s Warblers consists on insects (Molina et al., wed a low intensity of infection with 0.2 para- 1998), thus potentially leading to the ingestion sites per 2000 erythrocytes and was previously of parasite vectors, an usual mode of transmis- sampled and found uninfected in June. The ot- sion of Atoxoplasma. Parasites from this genus her infected bird was sampled only in October are considered pathogenic for birds, although and showed a moderate intensity of infection data are scant (Manwell, 1977). For example, with six parasites per 2000 erythrocytes. The Cooper et al. (1989) reported large number of three birds were aged as fledglings of the year. parasites in the liver and spleen of captive Gre- The individual infected by Atoxoplasma sp. enfinches Carduelis chloris with the condition was an adult female captured in September and known as «going light», which is characteri- it was not recaptured. The parasite infected sed by diarrhoea, weight loss, loss of appetite small lymphocytes and the intensity of infec- and ruffled feathers usually followed by high tion was low (less than 0.2 parasites per 2000 mortality. The only infected Cetti’s Warbler erythrocytes). was never recaptured but it was apparently in In accordance with previous reports, our re- good condition and no sign of illness was de- sults show that the Cetti´s Warbler is a species tected. with low prevalence of blood parasitism. The Although the effects of blood parasites on only previous record in Western Europe reports wild birds are very difficult to note in short- five uninfected individuals (Peirce, 1981) and term studies (but see Merino et al., 2000), it is the only other record for this species is one possible that haematozoan infections play an bird infected by Haemoproteus sp. (Moham- important role in birds’lives, as shown for do- med & Al-taqi, 1975). This record comes from mesticated species (Bennett et al., 1993b). Cet- Kuwait where the species is present only during ti’s Warblers are infected by two species of pa- some months per year and a different subspe- rasites considered pathogenic for birds, and cies is involved (C. c. orientalis instead of C. c. although the low prevalence and lack of appa- cetti). To our knowledge, these are the first re- rent, severe effects on the individuals infected LOW PREVALENCE OF INFECTION BY HAEMOPARASITES IN CETTI’S WARBLERS 271 point to an absence of impact of these parasites FREELAND, W. J. 1983. Parasites and the coexistence on population regulation, some effects may be of animal host species. American Naturalist, 121: obscured by the difficulty in capturing indivi- 223-236. duals with signs of illness. GARGALLO, G. 1997. Ageing of Cetti´s Warbler Cet- tia cetti by means of plumage characteristics. Rin- ging & Migration, 18: 14-17. ACKNOWLEDGEMENTS.—We thank the SEO-Mon- GODFREY, R. D., FEDYNICH, A. M. & PENCE, D. B. ticola ornithological group for their continuous effort 1987. Quantification of hematozoa in blood sme- that makes possible the long-term monitoring study ars. Journal of Wildlife Diseases, 23: 558-565. of passerines including Cetti´s Warblers. Dr. Robert GREINER, E. C., BENNETT, G. F., LAIRD, M. & HER- Adlard kindly provided an essential reference. This MAN, C. M. 1975. Avian hematozoa 2. Taxonomic work has been partly supported by DGESIC project keys and colour pictorial guide to species of Plas- PB97-1233-C02-01.