BTO: On song and already trying to breed

Song thrush ANL-140331-125822001
Song thrush ANL-140331-125822001
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Spring, it seems, is well under way and there is a growing chorus of bird song at dawn to announce its arrival.

Spring, it seems, is well under way and there is a growing chorus of bird song at dawn to announce its arrival.

Song thrush nest ANL-140331-125833001

Song thrush nest ANL-140331-125833001

One of the most evident of these early season singers has been the song thrush, a bird which often repeats the same note ‘thrice over’ within its song. The series of notes is actually somewhat more complex than it first appears, shifting and morphing as the singer dips into a wider repertoire. The notes have a shrill edge, more cutting than those of the blackbirds which are also in full song.

Both species have already initiated their first breeding attempts of the year and a search of the local ivy and other evergreen cover has produced a number of active nests, some with contents but others still under construction.

From the outside the nests of blackbird and song thrush can appear similar, based as they are on a foundation of moss and grass. With blackbird, this foundation is followed by a lining of mud to form a cup, inside which is a final layer of finer grasses and other plant material. In song thrush, the foundation of moss is followed by a layer of rotten wood that has been smoothed and bonded with saliva. There is no further lining, the thrush laying its eggs directly on to the avian ‘chipboard’ that it has created. It has been suggested that the lining reduces the impact of nest parasites.

The presence of this solid lining makes it very easy to identify a song thrush nest but, just in case you were in any doubt, the bright blue eggs are very different from the rather pale-coloured eggs of the more familiar blackbird.

Both species have suffered a decline in their fortunes over recent decades, with song thrush populations falling by nearly two-thirds since the 1970s and blackbird populations falling by 16% over the same period. Changing agricultural practices may be one of the driving factors but there are likely to be others.

The song thrush is a species that is often associated with the habit of feeding on snails, which it smashes open against some hard object – such as a stone or a paving slab. Snails are only an important food item for thrushes at certain times of the year, notably during late summer when the dry conditions make more favoured foods harder to find. For most of the year song thrushes will be feeding on earthworms and other soil-dwelling invertebrates, but they take a lot of caterpillars in early summer and fruit in autumn and early winter.

To hear song thrushes singing locally and to find a good number nesting locally is an encouraging sign. It looks as if it might be a better year for these birds than was the case last year, when the late spring brought with it some challenging conditions.