Insecticide spraying : its effect on passeriform populations of central Newfoundland

Woodworth, Carla (1980) Insecticide spraying : its effect on passeriform populations of central Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Bird populations were studied during the 1979 breeding season by means of the mist-net technique in 3 areas of central Newfoundland in an attempt to identify possible longer-term effects of the 1978 application of the insecticide Matacil. Raw data obtained for 2 of the areas during the 1978 breeding season were used for comparative purposes. Structural features of the vegetation were measured at all net sites in 1979. These data were subjected to a principal components analysis to determine relationships among the measured variables. The percentage variation of the distribution attributable to vegetation differences between net sites was determined for the adults and immatures of 7 passeriform species by step-wise multiple regression analyses. The numbers of adults and immatures of these species expected at each sprayed area on the basis of the vegetation were obtained from regression equations developed from the control area data. Blood parasite levels were investigated in an attempt to gain indirect evidence of the impact of the spray applications on the insect population and hence on the food supply available for insect-eating birds. -- The number of parulid immatures captured at the control area was higher than at the sprayed areas. Adults of 4 species occurred at the sprayed areas in lower numbers than predicted by the regression equations. Immatures of 6 species at Big Careless Cove Brook and 5 species at Little Careless Cove Brook also occurred in lower numbers than predicted by the regression equations. No trends were detected among the areas in the blood parasite levels of the birds. -- The 1978 aerial application of Matacil appears to have directly and/or indirectly affected the avian communities of the areas studied. The high numbers of immatures at the control area probably result from immatures invading the area to forage on the high density spruce budworm population. Comparably, the low numbers in the sprayed areas result from the immatures leaving the areas where the food supple has been diminished (presumably due to insecticide applications) to forage in areas of more abundant food supply. In view of the higher predicted than observed abundances at the sprayed areas for the adults and for the immatures of several species it is also probable that there was a depressed success rate in the sprayed areas.

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