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Some Blood Parasites of New Zealand Birds

Discussion

Discussion

Doré (1918) suggests that ". . . it may be found possible to connect the comparatively rapid disappearance of New Zealand native birds with the introduction of exotic protozoa through the medium of the imported fauna. . . ." Myers (1923) elaborates this suggestion, stating that " . . . the hypothesis of an introduced avian disease which might conceivably commit the same havoc among the indigenous birds as measles among aboriginal races of man . . . supplies perhaps the only theory which can even partially explain the wholesale disappearance of certain species from untouched areas either before weasels or stoats were introduced or before they or any other cause of sufficient magnitude had conceivably reached the area in question." More recently, Wingstrand (1947) lists disastrous epidemics caused among domestic birds by Leuocytozoon, saying, " . . . I would emphasize the necessity of taking also the blood parasites into consideration when the changes in the Swedish bird populations are discussed, . . .," and Fisher (1948) draws attention to the desirability of examining blood smears from birds imported into Hawaii in order to guard against the possible transfer of exotic haematozoa to indigenous birds.

A very full investigation of the haematozoa of New Zealand birds, both indigenous and exotic, will have to be made before any decision can be reached concerning the effect of these parasites on the native avian fauna, as Doré himself informed Myers (1923). It was felt that such an investigation lay outside the scope of this survey, especially in view of the protected status of most of the native birds and the great amount of time which would be required to trap sufficient numbers of each species to justify such a study once the necessary governmental sanctions page 14 were obtained. For the present, it is urged that blood smears should be taken from all livestock imported into this country, particularly domestic birds, and submitted to expert examination for the presence of haematozoa. This procedure offers the only real safeguard against the introduction of such parasites as the Simulium-transmitted leucocytozoa, which may cause fatal epidemics among ducks (O'Roke, 1934) and turkeys (Skidmore, 1932). The widespread Simulium australe might serve as a vector for these parasites in New Zealand. As Fisher (1948) remarks, "It seems insufficient to allow the entry of birds on the basis of a clean bill of health as testified by the importer or by a veterinarian in the country of export."

Apart from two species of penguins (Megadyptes antipodes and Eudyptes pachyrhynchus) which breed on the subantarctic islands south of New Zealand, from which Plasmodium relictum var. spheniscidae is recorded, the only indigenous birds as yet known to be hosts for haematozoa are Anas poicilorhyncha (Plasmodium sp?) and Anthus novaeseelandiae (Plasmodium sp?). In so far as the indigenous portion of the New Zealand avian fauna has been examined for haematozoa (Table 2), it appears to be exceptionally free of these parasites. No material has yet been examined from any of the migratory birds, which offer the only avenue other than the agency of man for the introduction of avian haematozoa into this country. It is of decided interest in this connection that Toxoplasma sp? is here recorded from Zosterops lateralis, a species which reached New Zealand apparently from Australia or Tasmania in 1856 (Oliver, 1930).

Australian native birds have a rich fauna of Trypanosoma, Haemoproteus, Leucocytozoon, Plasmodium, and Microfilaria, and Lawrence (1946) records a Toxoplasma from Passer domesticus in Sydney. Neither Trypanosoma nor Microfilaria have yet been recorded from birds in New Zealand. Cleland (1915) records Plasmodium biziurae? from the black swan (Chenopis atrata) = Cygnus atratus, one specimen of two examined in Australia being positive for this parasite. Following its introduction into New Zealand during last century, Cygnus atratus has become common and widespread, and is now regarded as a game bird. Smears from 99 specimens of this bird were examined during the survey, but all proved negative for haematozoa. Cleland and Johnston (1910) and Lawrence (1946) record a Haemoproteus from Zosterops lateralis in Australia. Two of 14 birds examined by the former authors and one of three examined by Lawrence were infected with this parasite. As Haemoproteus was not recorded from any of the 124 specimens of Z. lateralis examined during my survey, it seems likely that the parasite did not accompany its vertebrate host to New Zealand, or, at all events, has failed to become established in the Wairarapa, the part of the country from which my material was obtained.

None of the 95 examples of the common pigeon Columba livia examined were infected with Haemoproteus columbae Kruse, 1890, which has accompanied its host to most other areas into which this bird has been introduced. However, as page 15 no material has yet been examined from lofts infected with the arthropod vector of this parasite, the ectoparasitic fly Lynchia maura, it is too early to regard Haemoproteus columbae as definitely absent from New Zealand.