They're spreading very rapidly. Permanent residents at Rostherne Mere now, too. And in Timperley, this year they've become resident in Fairywell Wood. Given that in nature, there's no vacant niches, all the fruit, seeds, berries they consume would have been eaten by native wildlife. And as you say - the nest holes..
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Timperley life list c. 89 (ish). Barn Owl 4.11.19, Green Sand 27.8.19, Little Egret 13.2.19, ringtail harrier sp 20.10.18, Fawn Yawn 15.10.18, Grasshopper Warbler 15.4.16, Tree Pipit 13.4.16, Yellowhammer 5.4.15, Hobby May '11, Wigeon Dec '10
I know Dunham Park has a few. Trouble is, the visitors like them & there would be an outcry if they were culled; also Tatton Park, Wallasey Vale Park, Mobberley, Padiham (E Lancs)
If there were a campaign of culling, the advantage is that they're communal
This might be a controversial topic, but it would be interesting to see what other birders think about Ring-Necked Parakeets (=Rose-Ringed Parakeet)
There are some 30,000 throughout the UK, with the vast majority in Surrey, but small populations throughout including an expanding population in S Manchester nudging into N Cheshire. They're charismatic birds - until you consider their ecological threat. They compete successfully for nest holes with total disregard for native hole-nesting species of bird & bat. They belong in the Indian Subcontinent, with 2 ssp across Africa
My view is that this non-native species should be removed from this region while it's still practicable