COULD the increasing numbers of Blackcaps that spend winter in Britain hasten the spread of mistletoe on our trees?
The species is possibly one of only two that feeds on the parasitic plant's sticky white berries after which it customarily wipes its beak on the branches of the host tree, thereby depositing its seed.
This is just one of many fascinating theories explored by super-observant field naturalist Ian Parson in his latest book, Of the Trees and the Birds, which has just been published.
The relationship between many bird species and trees is evidenced all around us every day.
However, it is doubtful that many birdwatchers analyse as scrupulously (and entertainingly) as Parson who writes with special expertise and authority - he used to be a forest ranger, then a bird guide leading tours in Spain's wildlife-rich Extremadura region.
To his credit, Parsons writes not with any pomposity but with fetching a modesty.
Favouring a fireside-chat mode, his narrative crackles along at pace.
There is an endearingly cheerful curiosity to his approach, and his writing is frequently peppered with quirky and sometimes self-mocking wit.
He provides many fascinating insights - for instance, how certain raptors, such as Goshawks, sometimes disinfect their potentially bacteria-riddled nests with the fragrant green pine needles of Douglas fir trees.
Disconcertingly, he notes that Little Egrets risk poisoning the roots of the trees in which they nest with their accumulated droppings which apparently are rich in a toxic blend of ammonia and salts.
The author's 'cast' of birds - those mentioned in the extent - runs to 67, while that for trees reaches 57, so this is indeed a comprehensive survey.
Returning to mistletoe, the bird most associated with it is the Mistle Thrush which many associate with the same bill-wiping activities as the Blackcap.
But the author notes that, unlike the Blackcap, this species swallows the whole berry, which probably takes about 30 minutes to digest, so it spreads seed through its droppings.
This is an unexpectedly superb book which will delight both expert ornithologists and those whose interest in birds is more casual.
Handsomely illustrated, it costs £18.99 in paperback and can be obtained from Caithness-based publishers Whittles Publishing at www.whittlespublishing.com (01593 731 333).