19th October 2009, Monday

I have previously posted about my use of the BTO garden bird watch website.  This is the second year that I have supplied weekly records of our garden birds and I do enjoy the ability to compare our garden from season to season, and contrast it with national trends.  The scheme has picked up evidence of declines of greenfinch that can be linked to an emerging disease, and the sustained decline of familiar birds like the house sparrow.

This bird is the only species to be recorded in all 81 weeks I have contributed to the scheme.  We provide them with food, nest boxes, and patches of hay meadow as a source of insects for the young during the summer. Each evening, at around one hour before dusk these birds gather in an unexceptional looking patch of scrub at the bottom of our street and launch into a noisy chorus that gives the impression that there are a lot of birds around.


Numbers are hard to determine, although an existing chorus of birds was joined by a group of 26 the other day as I was taking these photos.  They are almost impossible to spot apart from the odd individual in a more exposed position at the top of a bush


 And yet a closer look at the data gathered over the summers of 2008 and 2009 shows that numbers of birds recorded in our garden over the six months between April and September fell by 41%.  Numbers of another widely declining species, the starling, were also down 28% over the same period.  Of course these declines are not powerful evidence in their own right because of the small sample size, however when you look at the data gathered by the 16,000 participants in the scheme the trends are more convincing and worrying.  The decline of the house sparrow is unrelenting over the past 15 years.  Whereas in 1995 the maximum number of gardens supporting house sparrows during one week was approximately 89%,  by 2009 this had fallen to around 73%.

I like to think that our corner of Northiam will not exacerbate these grim statistics, and that this year is merely a temporary blip. Time will tell. If you want to contribute to this scheme and make the data even more robust do consider signing up. You can never have too much data.