Once Scotland's commonest hawk, the kestrel needs help to reverse its decline

As I carefully rounded one of the river's wide looping bends, a hunched bird about the size of a small wood-pigeon came into view sitting atop a nearby telegraph pole and gazing intently down into the haugh or flood meadow.

It was a young male kestrel, the blue-greys on the plumage of its head and tail having not quite developed.

As I stopped to watch the small falcon, it made a shallow swoop into the icy meadow and quickly rose again with a field vole in its talons, no doubt relieved that the partial thaw had made hunting somewhat easier by revealing vole runs previously hidden beneath thick snow.

As the kestrel flew away, I reflected on the fact that had this exact same situation occurred 20 years ago, I might not have even given the bird a second glance such was the familiarity of the kestrel, which at that time was our commonest bird of prey.

It was abundant in the countryside and had adapted well to life in towns and cities, nesting in buildings and church towers.

A car journey along motorways would almost always be accompanied by at least one sighting of a kestrel hovering 30ft or so above the verge in its hunt for voles and invertebrates. So common was the kestrel along our highways that it was dubbed the "motorway falcon".

But since the early 1990s the kestrel population in Scotland has plummeted.

Breeding Bird Survey data shows that between 1995 and 2008 there was a 54 per cent decline, with numbers falling a further 64 per cent from 2008 to 2009.

This compares unfavourably with England, where between 1995 and 2008 there was only a 3 per cent decline, which hastened to 29 per cent between 2008 and 2009.

The situation is so worrying that RSPB Scotland is now calling for urgent funding to establish a research programme to shed some light on this plunge in numbers.

According to the organisation, there are a number of speculative theories for the decline, with the fact that they are only conjecture reinforcing the need for definitive research.

One possibility puts the finger on changes in the natural population fluctuations of field voles, the kestrel's principal prey.

There is some evidence to suggest that the typical four-year cyclical pattern of voles involving boom and bust has become less pronounced due to climate change, taking away the opportunity for kestrels to capitalise on bountiful years.

Another theory lies in the significant afforestation that took place in the past few decades of the 20th century, with the young plantations initially providing excellent vole habitat, which in turn boosted kestrel numbers. Many of these plantations are now reaching maturity and are no longer good for voles.

Other suggestions include secondary poisoning from rodenticides and changes in land use. Or could it be due to increased ecological competition from buzzards, which increased by 38 per cent between 1995 and 2008?

Perhaps it is a combination of the above, but whatever the reason, research is urgently required because kestrel numbers are getting so low that if they fall any further it would become statistically difficult to chart population trends.

Professor Jeremy Wilson, head of research at RSPB Scotland, says: "When a crash in sparrowhawk and peregrine falcon populations occurred in the 1950s, caused by the use of early-generation pesticides in agriculture, only a concerted research programme uncovered these causes, allowing the problem to be resolved and numbers to recover.

"Just as was the case 50 years ago with sparrowhawks and peregrines, a research programme is urgently needed to shed light on what the causes (for kestrel decline] may be."

This article was first published in The Scotsman, 30 April, 2011