There has been a large population decline of the song thrush Turdus philomelos in Britain during the last three decades, which has reduced breeding densities on farmland by nearly 70% between 1968 and 1999. Survival of birds in their first year of life after fledging was shown to have a great impact on population changes. Changes in survival in the first winter are sufficient to have caused the song thrush population decline. Earthworms and other soil-dwelling invertebrates form a large component of the diet of song thrushes, particularly between December and May. Earthworms move deeper into the soil and/or become inactive during periods of cold weather and hence become less available as prey for song thrushes. Reduced availability of invertebrate food could explain reduced survival in the winter.
There has been a large population decline of the song thrush Turdus philomelos in Britain during the last three decades, which has reduced breeding densities on farmland by nearly 70% between 1968 and 1999. Survival of birds in their first year of life after fledging was shown to have a great impact on population changes. Changes in survival in the first winter are sufficient to have caused the song thrush population decline. Earthworms and other soil-dwelling invertebrates form a large component of the diet of song thrushes, particularly between December and May. Earthworms move deeper into the soil and/or become inactive during periods of cold weather and hence become less available as prey for song thrushes. Reduced availability of invertebrate food could explain reduced survival in the winter.
Source: Robinson RA et al. (2004) Journal of Animal Ecology 73: 670-682
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