Regarding Magpies, in years gone-by there were little or no cars, and Magpies were not able to survive the winter as easily as they are now due to the high levels of roadkill, especially in rural areas. This, along with other factors such as urban adaptation have led to the Magpie being hugely successful (UK population increasing 6% per year since 1940), which IS having a big impact on songbird numbers, due to egg/nestling predation. People need to realise that nature will not "find its own balance", or any of the other cliches so readily banded about by ignorant armchair "nature lovers", the only effect a thriving population of predators (such as the Magpie)not solely dependant on songbirds will have is to futher decimate declining species until localised extinction occurs, after which it will simply shift to another food source.
I work in Wildlife management, and I know for a fact that the RSPB (although publicly denying the need for corvid control for fear of losing members)shoots Magpies and other Corvids and uses Larsen Traps to control these birds on their Reserves and Ternaries. They would not do this if it were not necessary!!!
New research recently published in the Journal of Applied Ecology showed that where there were no magpies present, the reproductive output of song thrushes was much greater. This was well illustrated by two maps, one showing the distribution of magpies in Britain, the second showing the breeding success of song thrushes, and they demonstrated perfectly that where magpies were absent song thrushes thrived. A report entitled 'Large-scale spatial variation in the breeding performance of song thrushes and blackbirds', written by biologists from the British Trust for Ornithology (BTO) and the University of East Anglia, concluded that nest failure rate during incubation increased significantly where Corvids were present, and that most predation was by the smaller Corvids, particularly magpies. The significance of this report is that it is very large and thorough, and backs up the work performed by other biologists on nest predation in urban parklands by magpies, which is having a considerable impact on the local blackbird population.
Please consider these points, whilst a magpie may be entertaining to watch and certainly striking to look at, we could lose the dawn chorus altogether in years to come if we do not do something to control its numbers, and help songbirds in other ways such as winter feeding and providing nesting cover (uncut hedges etc).
Songbird Survival is an excellent charity working to help songbirds, and is well worth a look.
