CANARY IN THE MINE. “The House Sparrow Passer domesticus population in Britain suffered a major decline in the 1920s, particularly in built-up areas, which coincided with the replacement of the horse by the internal combustion engine.” Not just from toxic fumes but from the loss of the oat spill from horse feed bags.
https://www.britishbirds.co.uk/wp-content/uploads/article_files/V96/V96_N09/V96_N09_P439_446_A004.pdf