Population changes of species for which our best long-term trend estimate from CBC/BBS (usually over 51 years) or from WBS/WBBS (a maximum of 43 years) shows an increase of more than 50% are shown in Table C1. There are 28 species listed, two fewer than in BirdTrends 2019; the increases for Pied Wagtail and Robin are now just below the cut-off and they are no longer listed in the table. Twenty-one of the species have more than doubled their population size over the periods in which they have been monitored (25–51 years).

Table C1 is led by Buzzard, by a wide margin, but it should be noted that seven of the fastest-increasing species in this report are actually not included here, because their monitoring data cover too short a period. The UK's non-native population of Ring-necked Parakeets is estimated to have risen by 1,776% (more than a 18-fold increase) over the 23 years 1995–2018. Arguably, however, this is more a conservation problem than a success! Mandarin Duck (+457% over 1995-2018) is another fast-increasing non-native species. Undoubted success stories are the growth during 1995–2018, estimated through BBS, of Little Egret, which has increased by more than 20-fold, the re-introduced Red Kite (+1,738%), Cetti's Warbler (+417%), Gadwall (+253%) and Barn Owl (+251%), and and. The headline trend for the Cetti's Warbler, a recently established native species, comes from CES rather than BBS with CES estimating a higher increase than BBS (691% during 1992–2018), even though the trajectory has been moderated by recent cold-weather-related setbacks. An eighth species, Stonechat, is also not included in the table but has also more than doubled its population over the period 1995–2018 (+118%).

Four groups stand out among the increasing species: corvids – especially Carrion Crow, Magpie and Jackdaw; doves – Collared Dove, Stock Dove and Woodpigeon; woodpeckers and other smaller species of woodland and gardens; and some waterbirds. Corvids appear to have benefited from changed gamebird management practices in recent years, and the larger doves from the increased acreage of brassica crops (particularly oilseed rape).

The majority of the third group are species primarily of woodland that are also common in gardens in some areas: Great Spotted Woodpecker, Green Woodpecker, Nuthatch, Blackcap, Wren, Great Tit, Coal Tit, Long-tailed Tit and Goldcrest. The reasons for these increases are presently unclear but may, in many cases, relate to improved feeding opportunities in gardens. Reed Warbler, an insectivore, has been expanding its range northwards and westwards and might be benefiting from climate change (Eglington et al. 2015). Declines on CES plots suggest the benefits might not be universal, with the habitat quality in 'core' sites possibly decreasing, while warming climates facilitate the colonisation of new sites.

A number of species associated with freshwater habitats are becoming more abundant, although differences between their ecological requirements make it unlikely that there is a single causal factor common to all. For Mallard, the CBC/BBS increase was matched by a WBS/WBBS increase of 165% over 43 years. The long-term increases recorded for Mute Swan on both CBC/BBS and WBS/WBBS plots are likely to be the result, at least in part, of banning the use of lead weights by anglers, which took effect in 1986. Greylag Goose, Shelduck, Canada Goose, Coot and Goosander are other wildfowl among this report's increasing species.

Two widespread raptors have shown remarkable recoveries from low population levels after the banning of certain poisonous farmland pesticides in the early 1960s, assisted by lower levels of illegal predator control. Buzzards increased in England by 856% between 1967 and 2018. Sparrowhawks, too scarce for CBC to monitor until the mid 1970s, show a 79% increase over the 43-year period from 1975 to 2018. However, their recovery appears to have been completed earlier than Buzzard's, and the population is now in moderate decline (for unknown reasons), prompting a lower level alert to be raised over the 25-year period (see Latest long-term alerts).

While Pheasant holds a place in this table, its increase in census data has been driven largely by increasing, but poorly quantified, scale of releases of artificially reared poults for shooting. Corvids, and other generalist predators, may also have benefited, exploiting both through the food provided for poults and the high mortality of poults, resulting in an abundant level of carcasses.