Friday, 12 September 2008

No Yanks

Well apart from a few American waders on the Azores and on the continent that system didn't really produce anything. Just shows that even when favourable weather occurs, unless there are an interplay of a number of factors, the system will be barren. The weather chart above shows the conditions the day before two Yellow Warblers, a Northern Waterthrush and a Solitary Sandpiper turned up in Ireland in late August this year. To my eye there is a fairly good situation for American vagrants with s a good westerly airflow but I have seen these conditions before that do not produce such an impact. The factors involved with generating transatlantic vagrants are quite complex- conditions in the source area must be suitable for migration inception and of course the birds have to be there and ready in the first instance. The condition of the migrants affected must also be taken into account- the species suite and their physical vulnerability to vagrancy. Once inception has occurred the deflection towards Europe has to occur, presumably ship assistance comes into play and then there is the factors of actually finding the birds when they make landfall. Because there are so many factors to consider, prediction is not an easy game.

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