BTO: Mistle thrush is an early starter

Mistle thrush. Picture: BTO/Edmund Fellowes
Mistle thrush. Picture: BTO/Edmund Fellowes

While the mild weather has prompted a number of our bird species to deliver breeding season song somewhat early this year, there are others whose breeding seasons are already well advanced, writes Mike Toms, from the BTO.

One such early nester is the mistle thrush, a robust looking bird, larger in size than both the familiar song thrush and blackbird to which it is related.

The local name of ‘storm cock’ alludes to the mistle thrush’s habit of delivering its song early in the year, often during the stormy weather of February when other birds are quiet. Singing birds perch high in the bare branches of a tree and it is in such trees that the nest will ultimately be built. The nest itself is a large cup of grass, moss, roots and leaves, bound together with mud and rotten wood. This layer of mud is characteristic of several of our nesting thrushes, but it is not obvious as the mistle thrush goes on to line the nest with finer plant material. Only in the song thrush is the mud and wood lining left bare to receive the eggs.

As the recently published BTO BirdTrends report – www.bto.org/about-birds/birdtrends/2013 –highlights, mistle thrush populations have been declining since the late 1970s, with the breeding population falling by more than 50 per cent over this period. Although declines are being seen elsewhere in Europe, these have not been as pronounced as those occurring here in the UK. Interestingly, the pattern of decline within the UK varies with region and it appears that populations in the south-east of England, including East Anglia, are faring rather worse than those further north. This pattern is also being seen in a number of other species (as revealed by the recent publication of Bird Atlas 2007-11) and this has prompted scientists at the BTO to initiate research to establish what is going on.

Despite its large size and far-carrying song, the mistle thrush is often overlooked. This may be because many people are unfamiliar with the song (it sounds a bit like a less tuneful blackbird) or have trouble separating mistle thrush from song thrush. Observers may be more familiar with the mistle thrush later in the year, when family parties can be seen feeding on garden lawns and, when disturbed, may be heard to utter their characteristic ‘football rattle’ call.

Other individuals are familiar visitors to those garden bushes and shrubs still holding berries. Some mistle thrushes take up residence on such shrubs and attempt to guard the berries from other birds – their larger size gives these thrushes an advantage. By doing this they can make the berry stocks last longer, something that may prove to be important should a spell of late winter snow and ice put in appearance. Mind you, given how mild it has been this year, most mistle thrushes will be already well into breeding mode.