Chris Packham was very careful with his words, yet he still misleads us when he says magpie predation does not in itself cause population declines of other birds (Change is coming, June). It depends on your starting point. As indicated, farming intensification has been the main cause of population declines in farmland songbirds, but predation can be an additional factor which may or may not be important.
However, it is more likely to be relevant today, given farming related habitat losses and the increase in magpies since the 1960s.
Magpies predate bird nests, they are much smaller than crows and are adept at moving through dense hedgerows where many farmland species nest. It has been shown that they can supress the productivity of breeding songbirds in those hedgerows in a modern farmland system. If breeding success is a factor that limits population size for a particular bird species in a given area, and sometimes it will be, then magpies can cause that population to decline. We can try and address these declines by changing farming, which may or may not work.
There is already a lot of good but expensive farming conservation practice in the UK today so, if we want to grow food and have farmland songbirds, it is unhelpful to brush over the potential effect of other factors.
Dr Rufus Sage
Game & Wildlife Conservation Trust (GWCT)