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Q. I am sure skylarks have not declined in my area. How do you know they have declined nationally?
A. Common breeding birds in the UK have been monitored since the 1960s, firstly by the Common Bird Census (CBC, 1962 - 1999) and more recently by the Breeding Bird Survey (BBS, 1994 - present). The CBC was a very intensive survey (8-12 visits in the spring) that accurately recorded trends in numbers of territories of all breeding birds on a site, and roughly 200 sites were monitored each year. The BBS is much less time consuming (2 visits in the spring) which will not accurately record trends on any one particular site, but the fact that in excess of 3,000 sites are covered annually makes the ability to identify national trends very powerful. The one flaw with the CBC method was that the smaller sample size and the distribution of volunteer survey areas meant it was not as representative of the whole of the UK as is possible with the much greater participation possible through the BBS. The CBC sites were predominantly in England, and most numerous in southern and eastern England. The two methods were run alongside each other for 6 years to check that the results that were generated were comparable, before BBS replaced CBC completely in 2000, and CBC is no longer continued as a national monitoring methodolgy. Full details of how the BBS is conducted can be found on the British Trust for Ornithology (BTO) website at http://www.bto.org/bbs/index.htm.
The skylark is an unusual example of a declining species in that it appears to be declining across the UK, and there are currently no areas where it is actually disappearing completely. As such, many would not be able to say with certainty that numbers in their area have increased or declined. Many would relate much more to the declines of species such as the lapwing or grey partridge, as nesting numbers found now have noticeably declined, or even disappeared completely, over the last 40 years. The evidence from consistent monitoring of common breeding birds is invaluable in giving early warning signs about trends in populations before localised extinctions make recovery work much more difficult and expensive. The understanding of the population trends of all common breeding species in the UK can be found on the BTO website. The skylark summary can be found at http://www.bto.org/birdtrends2007/wcrskyla.shtml.
One notable study showed that, if you divide the BBS sites occupied by skylarks into ones with no over-wintered stubble, ones with at least 10% over-wintered stubble and ones with at least 20% over-wintered stubble, skylarks have only declined seriously where there is no over-wintered stubble, and have not declined at all in areas with at least 20% over-wintered stubbles. It may be the availability of seed food through the winter or better breeding success in subsequent spring crops that improves the trends in areas with over-wintered stubbles. The solution to this is not to revert to 1970's cropping when a higher proportion of cereals were drilled in the spring, with the associated lower yields, but to look for solutions that can be integrated into modern, productive arable systems. An example is the inclusion of skylark plots into winter cereals, which take 0.003 of the field out of production but increase the number of skylark chicks produced by roughly 50%.
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