The British Trust for Ornithology (BTO) has published a series of 'average population density' maps on its website, showing the number of individuals per square kilometre for 49 common species of bird.
The density distribution follows an intuitive pattern for most species, but there are some striking exceptions. The majority of species are associated with lowlands, and therefore more thinly distributed in upland areas and northwest Scotland. Conversely, the meadow pipit is densely distributed in northern and upland areas.
Lapwing is a distinctly eastern species, with hotspots in upland fringes of Northern England. In England, swallows are noticeably more common in the Southwest than the Southeast, but swifts are highly focused on urban areas.
The maps are based on density data collected by Breeding Bird Survey volunteers between 2007-2009, and are paired with a second map showing changes in density.
The maps come with a large caveat, however: the modelling used has a higher uncertainty in upland areas, which might explain a lot of the patterns of distribution (there simply aren't as many bird recorders in upland areas).
The maps can be viewed here: