As Edward says its a whole range of factors that have caused the dramatic wildlife decline.Â
Old trees removed as they can fall on people will mean crevice nesting species have nowhere to live, the canals are now fully occupied by live aboards so disturbance will mean aquatic animals are affected, domestic predator numbers (cats and dogs) are probably at an all time high which causes disturbance and lack of prey (small mammals and birds). Petro horticulture sprays, lack of native plants for insects to use, no hay meadows, no livestock as agriculture is unviable which means no insects, no derelict buildings, all eaves are now sealed for energy conservation, ponds disappeared, paved over from gardens, astroturf rear lawns.
None of the Grand Design programmes or gorgeous George ever mention conservation in architecture…..
So it would be great if GLA did do more and maybe change the contracts for the parkland management.  Dedicate 30% to wildlife friendly measures.  Don’t chip all the fallen branches, leave large tree trunks, exclude people to protect veteran trees etc
However people can make a difference despite what the politicians do and No Mow May is an example along with the Wildlife Trust Campaign to make gardens wildlife friendly, along with the swift movement….
Just writing to a local paper, taking action in your own area, talking to your neighbours all makes a difference….
Just watched The Wild Gardener which although on a big scale 1 acre the same principles apply to a small area
https://www.bbc.co.uk/programmes/m00121fw. Now need to read William Robinson book The Wild Gardener…
How does Berlin do it?  Apparently they have a thriving nightingale population…..
Lastly despite the lack of response from politicians people across the UK are making a difference in their areas for swifts and wildlife in general!
Sorry for the rant…
Alistair