. Studies in bird migration . The movements from east to west, and vice versa, PLATE VI. Chart of North-Western Europe showing Typical WeatherConditions, with North-Westerly Winds, over the BritishIsles A depression lies to the eastward of and extends to our Isles ; whilepressure is highest to the north-west and south-west. Wind, circulatingcyclonically round the pressure minimum, being north-westerly andnortherly over the British area and the North Sea region generally. This type of weather is the most unfavourable of all for bird-movementsbetween the British Isles and the Continent. During i
. Studies in bird migration . The movements from east to west, and vice versa, PLATE VI. Chart of North-Western Europe showing Typical WeatherConditions, with North-Westerly Winds, over the BritishIsles A depression lies to the eastward of and extends to our Isles ; whilepressure is highest to the north-west and south-west. Wind, circulatingcyclonically round the pressure minimum, being north-westerly andnortherly over the British area and the North Sea region generally. This type of weather is the most unfavourable of all for bird-movementsbetween the British Isles and the Continent. During its prevalence the areafrom which we derive the great majority of the migrants in the autumn,and often our own shores from which they return in spring, are underunsettled weather-conditions, and hence adverse for these movements. On the other hand, the conditions prevailing over Iceland and thecountries to the south-west of us are not unfavourable for migration fromthose areas to the British Isles. (See also p. 177.) PLATE Reduced from Special Chart prepared at the Meteorological Office.] North-Westerly Type of Weather. Isobars are shown by black lines, with indications of the height of the —Arrows flying with the wind, show direction and force, thus :— y = forces 5 to 7 (velocity, 28 to 40 miles per hour). ^ = forces I to 4 (velocity, 8 to 23 miles per hour). Vol. I.] [To face p. 176. WEATIIKR INFIXTP:NCES 177 across the southern waters of the North Sea areundertaken under the favourable meteorological condi-tions which have just been explained—namely, the pre-valence of fine weather at the area of embarkation, andextending to the cast in spring and to the west inautumn (see Plate V.). Some observations on theautumn weather-intluences favourable and unfavourableto passages along this interesting line of flight willbe found in Chapter XVIII., which is devoted to anaccount of my bird - watchings on board the KentishKnock Lightship. Unfavourable Weather C
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