I had a look at my postcode and the presentation by the BTO is a tiny bit confusing. It looks like the postcode returns which electoral ward your address is in, i.e. a fairly small area, but the species data refers to one of the 10km squares that the Bird Atlas has coverage for, which from the presented image for me includes the whole of South Manchester and much of the Mersey Valley. Therefore the data for my postcode from 68-72 will predate the M56 and M60 motorways and the areas would have been drastically different back then.
This might explain how the website tells me that my area used to have Cuckoo, Yellow Wagtail, Corn Bunting, Snipe etc, surely birds from much more open country than we have today. The increasing species are almost all garden and park birds, this makes sense too. Some of the colonists are a bit harder to understand, but I would imagine that the Black Redstarts for me relate to the Manchester City Centre birds. The Plovers could be from Sale Water Park or anywhere like that. My postcode threw up Kingfisher and Dipper as colonists, presumably as the Mersey got cleaned up?
In fact for my postcode there are lots more gains than losses in terms of species, which must reflect some increased recording such as the Garden Birdwatch but also tells the story of the significant changes over 50 years. Consider the Mersey Vale Nature Park near me. In 68 this was still a busy railway line and the immediate area would have presumably been pretty polluted and horrible, so none of the birds that you get in the scrub and light woodland now. But along the river would have been pockets of farmland and more natural areas of boggy ground, which would give you the birds that have gone since then.
In terms of numbers I reckon it would be interesting to see the comparison just in that specific area, but clearly across the whole 10km square there will have been so much building and development that it is obvious that bird numbers will have dropped massively. And with modern farming practice the numbers would still have crashed if the land was being farmed now. The birds lose either way...
I suggest you are probably over thinking it. As the article states "A degree of detective work was required to assemble the different sources of information, particularly as recording was more fragmented back in 1970. Recording birds on such a large scale isnt easy and some numbers are difficult to ascertain. While this adds a degree of uncertainty to the figures for some species, we can be confident in the overall picture of loss."
What all of us birders do know is that bird numbers have definitely decreased over our own birdwatching years. Whether we have birded for 10 years or 60 years we all consistently say the same thing when we meet up; "There used to be more birds here". The same thing is said if I visit Pennington Flash, Irlam Moss, Watergrove Res, Audenshaw, Elton Res or anywhere else in the GM area. The same is said for most locations around the country (I can only think of a couple of seabird colonies that, in my mind, numbers seem to have grown in the 45 years I've consciously birded). Everywhere else, in all habits, there are just less and less bird numbers.
We also all know places where species have simply disappeared, whether its Corn Buntings on Carrington Moss or Wood Warblers in Etherow, we all associate our birding life with the demise of species that we had once taken for granted. Yes, there have been some winners. As a kid, I would never have imagined Little Egret or Cetti's Warbler to proliferate (and went on a mad twitch to see both). But overall we know there are just less birds.
Whether the number of 73 million is true or out by +/- 50%, it is still a sad state of affairs.
It is good to get engagement on the subject and good to debate it, and that is what has driven the BTO to produce this data. Get peoples reactions, get people talking about it, elevate the subject. Provide data to individuals, organisations, departments so that the issue can be recognised and, hopefully (and I know this is a massive hope), the right people try to put measures in place to reverse the depressing trend.
Looking at the square I live in and the adjacent one with Moore nature reserve.....
The square I live in started to be gentrified in the 1930s, then big push in the 180s/1990s as Warrington New Town expanded. I think that gives rise to some species "lost" that you think when on earth were they here. I've my Grandads old birding books and struggle to find for example Redstart as a breeder but there was a lot more countryside and Wood, especially ones without public access if some of his night time game / fish hunting smuggling stories were to believed.
The square where Moore nature reserve is looks "on expected trend" I've occasional records from early and late 2000s and certainly the decline has continued with the unmanaged decline of quality of land on the Forestry Commission Upper Moss Side next to Moore NR.
So I'd say the trends from the computer look "pretty reasonable" based on a limited pair of squares. Recent few years notable Obvs...Stock Doves seem to have nosed off a cliff the last couple years round here (not in the dataset I know) but Greenfinch (again last couple years not in the dataset) seem to be really bumping back.
I say that as I dont know of any Black Redstarts in Dane Bank / Denton West, never seen a Barn Owl in this area, or a Stonechat, Shoveler, and neither Ringed or Little Ringed Plover, they could be here somewhere but I dont know of any in this area and yet the website says they are all colonising.
It says Wood Warblers are declining in Denton West, that is surprising as I didnt know of any at all, again - there could be some but I just dont know of any. Same with Yellowhammer, declining, Im not saying there arent any but where were they? They used to breed on Reddish Vale (Denton side) years ago up until early 70s when I was a kid, my Dad used to tell us to listen for the song.
The Hawfinch used to breed locally apparently, that wouldve been brilliant to see those locally, my Dad used to take us to Leighton Moss regularly and a walk round the Silverdale area was usually in order as that was regarded as one of the best sites in the NW to see them, we never did, my Dad had already seen them and said they were notoriously difficult to see.
Green Woodpeckers used to breed on Reddish Vale too, used to watch them feeding on ants etc on the cow pats in the open farmland bit on the Denton side, never seen one clearly in Denton for probably getting on for 35-40yrs. It says they are declining but I think theyve already gone!
Thats just a few examples of what I mean, interesting but dont know what to make of it.
Click the link, put your postcode in and see what you have lost (you may be surprised);
https://data.bto.org/doorstep-birds/
The UK is home to 73 million fewer breeding birds today than it was in 1970, according to a new analysis by BTO researchers. By using data from BTO (mainly collected by volunteers) and partnership schemes, together with other published sources, BTO researchers have been able to estimate the size of UK breeding bird populations, both today and back in 1970.
