Increased breeding success

Nuthatch. Photograph by John Harding

Nuthatch has exhibited the greatest increase in productivity of any species over
the past 47 years, due to a combination of falling failure rates
and increasing brood sizes

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 for 28 species over the last 48 years, across a wide range of taxonomic groups. Population trends are also positive for 16 of these species, including raptors (Sparrowhawk, Buzzard, Barn Owl, Merlin, Peregrine), pigeons (Stock Dove, Woodpigeon, Collared Dove), corvids (Magpie, Jackdaw, Carrion Crow), and some small passerines (Nuthatch, Wren, Robin, Redstart and Pied Wagtail). It is therefore possible that increasing productivity has contributed to the population growth exhibited by these species over recent decades.

Conversely, 12 species (Little OwlTawny Owl, Kestrel, SkylarkSedge WarblerStarling, Dipper, Wheatear, House Sparrow, Tree Sparrow, Grey Wagtail and Yellowhammer) have declined in number as FPBA has increased, suggesting that a density-dependent reduction in intraspecific competition, or a retreat into better quality habitat, 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 not risen significantly for any of the 23 species monitored. Two species (Reed Warbler and Chaffinch) did show a significant positive trend in CES productivity in BirdTrends 2016, but the trend for both species is no longer significant following lower productivity in 2016.