The NGC was formally established in 1961 and collects bag statistics from about 650 estates or shoots each year. Each contributor completes an annual return form that provides the means to record 19 mammal species, namely Rabbit Oryctolagus cuniculus, Brown Hare Lepus europaeus, Mountain Hare Lepus timidus, Roe Deer Capreolus capreolus, Red Deer Cervus elaphus, Fallow Deer Dama dama, Muntjac Muntiacus reevesi, Sika Deer Cervus nippon, Chinese Water Deer Hydropotes inermis, Wild Boar Sus scrofa, Hedgehog Erinaceus europaeus, Grey Squirrel Sciurus carolinensis, Fox Vulpes vulpes, Feral Cat Felis catus, Weasel Mustela nivalis, Stoat Mustela erminea, Polecat Mustela putorius, Mink Mustela vison, Brown Rat Rattus norvegicus. All series are ongoing, with 2007 the last season included here (throughout, the year denotes the year in which a shooting season starts, e.g. 2007 refers to the 2007/08 season).

Species-specific annual bag indices are estimated using appropriate statistical methods (generalised linear models with Poisson error, logarithmic link function, log(shot area) and year and shoot as factors). Percentage changes over the periods 1961-2007, 1981-2007, 1986-2007, 1991-2007, 1995-2007, 1996-2007, 2001-2007 are evaluated after smoothing out annual fluctuations in bag indices (using generalised additive models). The 95% confidence intervals of the estimates are obtained by bootstrapping. To allow comparisons between years and sites, bags are expressed per unit area.

At the UK level, mammal species coverage is good except for Chinese Water Deer and Wild Boar. Coverage for England and Scotland is very similar, with the additional exception of Mountain Hare in England and Muntjac in Scotland. In Wales, species coverage is adequate apart from Mountain Hare, Roe Deer, Red Deer, Fallow Deer, Muntjac and Sika Deer.

At the UK level, the NGC data show significant medium-term (post-1960) increases in bag sizes for Rabbit, Roe Deer, Red Deer, Muntjac, Sika Deer, Grey Squirrel, Fox, Stoat, American Mink and Brown Rat, and significant medium-term decreases in bag sizes for Brown Hare, Hedgehog, Feral Cat and Weasel.

Temporal trends and spatial changes in distribution for Hedgehog, Red Fox, Feral Cat and Brown Rat, calculated from 1122 estates submitting bag records between 1960 and 1999 inclusive for one or more of the species, revealed a steady decline throughout the UK for Hedgehog, a decrease mostly in Wales and the southern half of England for Feral Cat, an increase in density across the UK for Fox and an expansion of range in northern Scotland and Wales for Brown Rat.