'Swifts are magical in the manner of all things that exist just a little beyond understanding'.

Helen Macdonald 'Vesper Flights'

William Hill was one of that class of Victorians and Edwardians that Hitchin seems so expert in producing- enthusiastic amateur naturalists who worked hard during the day growing the town's prosperity or educating its populace, but who used all their spare time to further our understanding of the natural world around us.

Hill and his chums- Latchmore, Lucas, Ransom et al- busily filled their notebooks with observations, maps and sketches and even collected specimens, all within walking distance of the town centre, often in the same local beauty spots that we enjoy today.

It was the bird enthusiast, Mr Hill, who noted a highly peculiar habit of the swifts that were flying over our town on a summer's evening long ago:

'…Swifts, after collecting together in the evening, ascend in companies to a vast height, there to spend the whole night on the wing, their screams being easily audible when they themselves have disappeared from sight.'

He later theorised that the ascending swifts were all males, possibly escaping the nest as 'the hen was sitting or brooding newly hatched young': a behaviour not just limited to birds, methinks.

In her recently published collection of essays, the acclaimed author Helen Macdonald also beautifully describes this mysterious ritual-like behaviour, referring to it as a 'vesper flight'.

In this highly recommended book, she also reveals that pilots have reported seeing swifts at altitudes of at least three kilometres, apparently in a state of suspended animation whilst still flying. And she points out that it is an activity undertaken at both dusk and dawn.

So, if undertaking an annual migration from southern Africa to Ickleford Road to then fly noisily over the Vic pub (which they do) as you sup your summer pint wasn't quite enough of a magical feat for you- they also seem to be regularly flying as high as possible for fun and have a kip when they get there. Now, that IS an impressive résumé for such a little bird.

Martins, swallows and swifts are all master aviators that gather insects on the wing, and it is these similarities that often lead people to believe that they are all closely related. They are not. The former two are in the same family but the swift is only a very distant cousin; a closer relative is the hummingbird.

Close-up, swifts are dark brown in colour- which looks black against a summer sky- the only colour variation being a very small paler patch on the throat.

The span of their scythe like wings is larger than that of the swallow and is disproportionally large compared to their small aerodynamic body. Both species share a forked tail, but the swift's streamers are noticeably shorter. It also has largeish eyes and a small bill capable of a deceptively large bug-catching gape.

They feed on the wing; they can mate in flight; they gather materials in the air for their nests and as we now know, they really can shut down half their brain to allow them to sleep whilst on the wing.

These evolutionary adaptations- a few of which they share with the migrant swallow- allow them to undertake a staggering 22,000 km (14,000 mile) return journey to the UK every year from Southern Africa.

It must be these unusual behaviours and impressive feats that gave the swallow its once archaic name- 'the devil bird'- and it's worth considering all of this when you see them fly over your home.

Upon arrival, swifts will return to their traditional nesting sites in the eaves or roof cavities of older buildings, as they are firmly an urban bird. But therein lies the problem: demolition, new building design and home improvements often result in habitat loss, so just like the returning swallow, swifts also need our help.

You can buy swift boxes to fix under your eaves- I have one myself- but some patience may be required before you see an occupant. The siting of the box is important as birds approach the nest hole at full speed, so they will need an unobstructed flight path. And as with the swallow, remember to make your garden even more bug-friendly if you can.

Pairs of birds will raise two to three chicks when here in Hitchin, if all goes well. Both parents will help to keep the eggs warm and once the brood is hatched, mum and dad will take turns in gathering bugs to feed the hungry mouths. After 50 or so days the fledglings will leave the nest, taking an initial leap of faith and then flying-off as fully independent birds. The lengthy return trip to the ancestral grounds in southern Africa follows soon after.

And finally, so adapted are swifts for the life on the wing, they have evolved tiny legs that are nearly useless for movement on the ground. When they are forced down their movement on terra firma resembles an ungainly tummy-based crawl. Such stricken birds are likely to die, however, as this lack of mobility makes taking-off again almost impossible.

The arrival of no other bird in the spring generates such passion and excitement for us townies. Swallows are lovely, but as we know, they mainly limit their presence to the wide-open fields over yonder. But the mysterious swift truly lives amongst us and is part of our urban existence- when you hear that joyous screech of a gang whizzing overhead you are welcoming back old friends and know that summer cannot be far behind.

This year they are a little late in arriving and this could be due to the current cold, wet and windy weather. Swifts have been known to divert hundreds of miles to find fairer weather so that they can feed, as many bugs don't fly in the rain.

I was excited to see my first swifts last Thursday (6th May). About half a dozen birds flew over Bearton Road but their altitude and purposeful speed suggested they were aiming for elsewhere, so the wait for our noisy summer lodgers continues.

Once here their stay with us will be shorter than that of the swallows. Swifts will start leaving in August with all the of them left by early September. When the skies fall silent at that point it can be a sad day for those who value their screeching summer presence. It also presages the end of summer.

But hey, that's for another day: we will soon be celebrating the appearance of these wonderful visitors to Hitchin's skies once again, bringing summer in their wake and what could be better than that?

Watch the skies.