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Migrations of the Silver-Y Moth (Plusia gamma) in Great Britain

Katherine Fisher
Journal of Animal Ecology
Vol. 7, No. 2 (Nov., 1938), pp. 230-247
DOI: 10.2307/1157
Stable URL: http://www.jstor.org/stable/1157
Page Count: 18
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Migrations of the Silver-Y Moth (Plusia gamma) in Great Britain
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Abstract

1. Records of the presence and movements in Great Britain of the moth Plusia gamma L. from 1932 to 1937 have been collected from amateur Lepidopterists and others by the Insect Immigration Committee of the South-Eastern Union of Scientific Societies. The moths have been seen in varying numbers in each of these years, and an account of their distribution in each year is given. Only two winter records have been received, although such records were specially asked for. Both these concerned pupae. 2. About fifty records give the direction of flight of the moths. From these it is shown that there is a general tendency for northward movements to preponderate in spring, and southward movements in autumn. Westward immigration from across the North Sea seems to occur regularly in mid-August. 3. A study of records in which direction and strength of wind are given show that wind direction has little or no effect on the direction of migratory flights, and that migrations can take place in adverse winds of Force 4 (13-18 m.p.h.) or in cross winds of Force 5 (19-24 m.p.h.). 4. Possible starting points of migrations have been chosen by prolonging the line of flight backwards from the point of observation to the nearest point on the Continent, and weather conditions for the period immediately preceding the flights have been studied. There appears to be a tendency for migrations to begin in periods of rising barometer, rising or steady temperature, and light or moderate winds. Wind direction at presumed starting points seems to have no influence on the direction of migration.

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