THE DEMOGRAPHY OF BLACKBIRDS TURDUS-MERULA IN RURAL HABITATS - IS FARMLAND A SUBOPTIMAL HABITAT

1. A population of 54-76 pairs of European blackbirds Turdus merula L. encompassing woodland, farmland and edge (wood/farm boundary) habitat s was studied to investigate whether farmland is a sub-optimal habitat for a bird species whose ancestral habitat was woodland. 2. Woodland was occupied at a higher density than farmland, but there was also var iation within habitats, 'hot-spot' areas of woodland were occupied at high density, `sparse' areas at low density, while other areas were co mpletely unoccupied. 3. There was no effect of habitat or territory ty pe on survival, although movements between years were more likely to b e from farmland to woodland, and from sparse to hot-spot territories t han vice versa. 4. There was a higher proportion of young males in far mland than in woodland, and in sparse territories compared to hot-spot territories: but there was no difference in the age structure of fema les across habitats. 5. Timing of breeding and clutch size did not dif fer between habitats or territory type. but farmland females laid smal ler eggs than other females. 6. Reproductive success was low in all ha bitats (only 19% of attempts produced any fledglings), but there Mere significant differences between habitats in various measures of reprod uctive success. Success in farmland and woodland was similar, but hot- spot territories tended to be more successful than sparse territories. Predation was the major cause of failure. 7. Our results indicate tha t farmland blackbirds exhibit certain characteristics of populations i n sub-optimal habitat, but the effect of habitat on reproductive succe ss probably operated at a finer scale than this relatively crude habit at classification. 8. The distribution of breeding blackbirds is discu ssed in relation to ideal free and source-sink models.