Our best overall measure of breeding success is Fledglings Per Breeding Attempt (FPBA), calculated from brood sizes and nest failure rates, which indicates the mean number of young leaving each nest in a given year.
FPBA has increased significantly over the last 46 years for 31 species, across a wide range of taxonomic groups. Population trends are also upward for 16 of these species, including raptors (Sparrowhawk, Buzzard, Barn Owl, Merlin, Peregrine), pigeons (Stock Dove, Woodpigeon, Collared Dove), corvids (Magpie, Jackdaw, Carrion Crow, Raven), and some small passerines (Reed Warbler, Nuthatch, Wren and Robin). It is therefore possible that increasing productivity has contributed to the population growth exhibited by these species over recent decades.
Conversely, 12 species (Tawny Owl, Kestrel, Skylark, Starling, Dipper, Wheatear, House Sparrow, Tree Sparrow, Grey Wagtail, Meadow Pipit, Yellowhammer and Corn Bunting) have declined in number as FPBA has increased, suggesting that a density-dependent reduction in intraspecific competition may have enabled breeding success to rise.
CES ringing data integrate productivity across the whole season, including juvenile survival in the first few weeks or months after fledging. According to this measure, productivity has risen significantly for just one species, Chaffinch; the discrepancy between this trend and the decline in breeding success identified by the NRS warrants further study, but may be due to increasing survival rates post-fledging.
This report should be cited as: Robinson, R.A., Marchant, J.H., Leech, D.I., Massimino, D., Sullivan, M.J.P., Eglington, S.M., Barimore, C., Dadam, D., Downie, I.S., Hammond, M.J., Harris, S.J., Noble, D.G., Walker, R.H. & Baillie, S.R. (2015) BirdTrends 2015: trends in numbers, breeding success and survival for UK breeding birds. Research Report 678. BTO, Thetford. www.bto.org/birdtrends