Sunday, 29 September 2013

Bird timetables

Red-rumped Swallow (John Hawkins)
One of the pleasures of birding, especially when visiting certain favourite places regularly throughout the year, is to mark the changes through the year with the arrival and departure dates of birds. The former are much easier to record - the first swallow or cuckoo of the spring is a simply a case of seeing (or hearing) the bird and scribbling the fact down in one's notebook (and in the old days perhaps dash off a letter to the local newspaper!), But unless one is methodically noting down every sighting of say swallows in the autumn, you are never quite sure when your last observation of the year will be until they have gone. Our family of Red-rumped Swallows are still around the garden and roosting in their nest by our kitchen door every night - but for how long? On the other hand, a friend posted a few days ago the arrival of a wintering Robin nearby, which means that any day now we should also be hearing them in the garden.

The phenology of birds' migration (i.e. the study of the timing of arrivals and departures) therefore adds a lot of spice to days in the field. At the peak of migration times, in spring and autumn, each day brings the prospect of seeing a newly arrived bird. Thus seeing the first Red-rumped Swallow of the year here may well be the highlight of day's birding in late February, whereas throughout the rest of the spring and summer, they will be familiar birds, seen every single day - with "our" nesting birds giving special joy of course. When we have moved in to a new area (it happened in Colombia, India and then Spain in 2004), one of processes of personal ornithological discovery is getting familar with the phenology, the timetable, of our local birds. Another friend here, and excellent local birder, Sergio Mayordomo has painstakingly gathered data from local bird reports over the last 15 or so years to produce a table of the arrival and departure patterns of migrant birds in Extremadura- literally a migration timetable. You can see it on this link:

http://birds-extremadura.blogspot.com.es/2013/08/phenology-of-migrant-birds-in.html

It is a great piece of work and in some ways I wish it had been around when I first came to Extremadura - but I am rather glad it wasn't - it was a source of personal fascination to navigate through phenology and discover some of these patterns myself.

There is more nowadays to this sort of study than simply marking the seasons. Phenological studies are showing us how birds are being affected by climate changes. Research has shown how Reed Warblers are now arriving in  western and central Europe 14-21 days earlier than they did 40 years ago. In southern Germany Schaefer and his team showed that the start of egg-laying moved forward by two weeks between 1973 and 2002. Earlier breeding in Reed Warblers is increasing their clutch size, their breeding success and the number of pairs that have second broods. This may be a factor to explain their increasing population. But some species which winter further south may have less flexibility because they have to finish their annual moults in southern Africa and are therefore not able to move their departure dates forward. Thus birds like Icterine Warblers are showing fairly stable arrival times in central Europe but may be suffering because the earlier springs mean that they are no longer synchronising their breeding with the peak of food availability to feed their young. In many European countries now, bird conservation bodies are taking a closer interest in pheonology of migrant birds. Like the canaries in the mines, or birds of prey hit by pesticide use, birds are proving once again their huge value as indicators of environmental health.

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