|My first Woodchat Shrike of 2015 (Martin Kelsey)|
There is variation of course, brought on by prevailing weather, or the physical condition of the birds themselves. Cranes will wait for a sunny day with little wind to set off north-east out of Extremadura, anytime in the second half of February. The perturbations to normal patterns add spice to the observer of course. Over the last few days there has been an unusually large passage of Garganey through Extremadura, with drake-dominated parties of twenty or even thirty birds turning up at water bodies across the region. On a brief visit to Alcollarín three days ago, I watched 23 birds, males stiffly bobbing their heads, giving their rattling display calls as they weaved and swerved around the out-numbered females. I could have happily spent hours watching these, my favourite of all ducks. As during my early birding years in Britain, there is an exotic ephemeral element to Garganey, wintering in tropical Africa, they make brief appearances in early spring on sometimes the most modest of pools. Two days later, just before watching the Woodchat Shrike, a careful check of the reservoir revealed just four Garganey left: three drakes and a duck.
Through natural selection, there are changes happening with migration timing and direction. With climate change and the shifting forward of annual cycles of many plants and insects, there can be a selective advantage on those birds which migrate earlier, to keep up as it were with the supply of resources on which they depend. As well as individual differences, there are differences too between species on how flexible or adaptable they can be. Reed Warblers are now returning to breeding grounds in Europe 14-21 days earlier than they did 40 years ago, whereas Great Reed Warblers with their longer migration routes are only arriving a few days earlier than before.
|Great White Egrets (Martin Kelsey)|