Monday, 6 October 2008
A week of megas
According to Birdguides, they recorded 19 new megas between 25th September and 1st October. Brown Shrike, Brown Flycatcher, Eastern Olivaceous Warbler, Syke's Warbler, Siberian Thrush, White's Thrush, Pallas' Grasshopper Warbler and many more expected vagrants were found. This was an excellent example of a vagrant influx, deposited mainly in the Northern Isles and the NE coast of England. The weather system was characterised by a major high pressure generating a strong easterly airflow- 'a conveyor belt' across the near Eurasian landmass. If there is awareness of what to look for, in terms of weather systems, it is possible to make some predictions about such events. High pressure systems are often involved with vagrancy influxes. In such conditions vagrants can occur over a broad front but typically are concentrated in vagrant traps- remote islands and headlands. These sort of conditions are not to be confused with classic fall conditions. 'Falls' occur on frontal systems and involve large numbers of common migrants in localised areas. There is often little association with falls and an influx of vagrants.