WHERE have all the house martins gone? I've seen a few hawking over the Hillfoot villages and also by the edge of Alloa, but nowhere near the numbers as in previous years.

Swifts, too, are scarce this year, which is a pity, for I miss watching them whoosh between houses, changing tack and direction with the sureness of a bat.

I suspect unseasonably cold weather in May over central and southern Europe held up the migration of both swifts and house martins, with many deciding to abandon venturing further north.

Such fluctuations, whether local or national, underline the frightening array of dangers faced by our summer migrants each year.

A migration across the parched Sahara desert is fraught enough, without then having to face sea crossings, songbird hunters in the Mediterranean and the ever-present threat of inclement weather.

But at least sand martins are about in good numbers down by River Devon, occupying their nesting burrows by sandy cuts in the river.

But they, too, have their own threats to face and a marauding American mink can easily destroy a colony in no time at all.

There do seem to be fewer mink on the river compared with the recent past, probably because of competition with otters.

Interestingly, I discovered a mink the other week when walking by the river near Dollar, and when it saw me, rather than jump into the water, it decided to climb up an alder for safety, from where it watched me from a branch about 15ft up.

Their agility on both water and land, underlines why they are such formidable predators, and a threat to many of the Devon's native creatures, including sandpipers that nest on shingle banks in the river.

Of course, it's not their fault they are here, it is ours, with the animals being the descendants from escapees from mink farms in times past – just one more example of our capacity to upset the natural balance and cause real harm to the environment.

@BroomfieldKeith