Features

Aerial acrobats

Martin Brennan welcomes the return of the Swift and the hatch of the Mayfly, two of summer’s quintessential visitors.

They’re back, they’re back”. Such was my delighted exclamation elicited in response to the first calls of the returning Swifts when I was Dublin city-bound about ten years ago. This utterance was accompanied by a rush to the window to get visual confirmation to further satisfy my excitement. Swifts, for me, epitomize, above all other returning summer migrants – even the Cuckoo – the joy, freedom and exuberance of summer. They are one of the latest returning birds, and back then arrived punctually on the 5th of May each year – at least I didn’t hear them before then.

Last year for the first time however, they returned in April (27th – in Sligo town), although being rural-based I have no personal records for the intervening period. Global warming is the probable cause for the earlier return, reflecting as it does changing patterns in bird behaviour and movement. Their distinctive screaming calls, delivered in high speed flight, and picked up by the receptive ear, announce their presence, often long before they are seen, as they tend to fly high, particularly in good weather. And giving cause for concern, Swifts among others, are showing steady annual declines in populations here.

Masters of the air

Now I discover in “Nature Cure” that they similarly excited Richard Mabey, its author, and generated a similar vocal response. He has wonderfully descriptive passages therein on their fascinating high speed flight games and displays, and describes these as “little short of pyrotechnic selfindulgence. They are the most pure expression of flight” he says and are “our twenty-first century equivalent of the Romantics’ nightingales – cryptic, rhapsodic, electrifying – but happy to be all these things at high speed in the middle of the urban landscape”.

Although sometimes mistaken for Swallows (they are a different order), Swifts have a very distinctive arrow shape and flight pattern, and are primarily urban-living. Their wing beats are so rapid that, to the human eye, they appear to beat alternately. Such powered, high speed flight, characterized by rapid bursts of flickering wing beats, followed by long slow glides on stiff wings, are made all the more fascinating when performed by tight flocks flying low over rooftops and between buildings at high speed.

Truly fascinating and mysterious birds, they have dark, almost black or sooty plumage, with a pale chin, scythe-shaped wings, “cigar shaped bodies” and short forked tail. Truly an enigma among birds, it was generally accepted that until they matured they spent their entire lives on the wing. Amazingly, I now learn, contrary to such popular belief that they do come to earth to roost at night: “A common myth asserts that Swifts spend the first three years of their lives flying, never landing even to sleep. Only the need to reproduce brings them down. The reality is that Swifts roost in groups overnight, usually in hidden spots, and then only when darkness forces them to stop hunting insects”¹. A very surprising revelation! While there are ninety two species of Swift worldwide, it appears to me that he is referring to the European species, although Tudge² argues separately that this species is one of the few exceptions to this contention.

Building on the wing

Swifts legs are very short making perching uncomfortable and making them almost helpless on the ground. Their long, narrow wings exacerbate the problem, rendering them unable to take off should they accidentally come to ground. They need to drop into the air for take-off, like bats, similarly insectivorous, which also have similar restrictions on take-off and landing. They nest in cavities, usually in buildings, under eaves or behind fascias. Their aversion to perching results in their adaptation to gathering air-borne material for their nests on the wing. The nests are constructed by most swift species while hovering. They produce an hormonally controlled dense, yellowish, sticky saliva providing a tool of extraordinary versatility. It is the material from which the base or foundation of their nests is constructed, into which twigs are pushed to form a platform. Ultimately a cup-shaped nest is formed, with saliva acting as the glueing agent for the remaining materials used. At the end of summer they return to Africa for the other half of their nomadic lives.

Fisherman’s friend

Another smaller creature whose flight also generates much excitement, particularly amongst anglers, is the Mayfly. It spends up to two years as a nymph in water, before emerging, and metamorphosing into an elegant adult winged insect. Mature nymphs tend to emerge en mass over a short period of a few days, usually in May, timing varying with location and local conditions, with smaller numbers emerging over a more extended period, both before and after the main body. The nymphal skin (shuck) splits open and the winged insect emerges. This newly-emerged winged form, known as the sub-imago, is drab in colour with opaque wings. Uniquely among insects they have a second adult phase. Shortly after emerging they undergo a further moult developing into a second winged phase, the sexually mature imago (fully developed adult), more brightly coloured, and with sparkling translucent, stained glass-like wings and longer tails – usually three – and take to the air in swarms. These phases are known to anglers as the dun and the spinner respectively, on which they model artificial flies.

The nymphs are usually drab or brownish in colour. And because they are food for fish and larger invertebrates they spend much of their lives hidden under stones or among vegetation. Growth can take from a couple of months to two years, according to species, and may involve as many as twenty seven instars, or moult stages. They feed on algae and other detritus, and some species are carnivorous. Depending on the species they may be found in lakes, rivers or streams, and due to their requirement for unpolluted water during the extended period of their larval stage they are good indicators of water quality.

Dance of the Mayfly

Life in the adult winged stage of its life cycle is short, only a few days at most, as their mouth-parts are reduced in size and they do not feed. Their function is to reproduce and create the next generation. Their flight is quite a spectacle as they dance and float in large swarms over the surface of the water, rising and falling in waves or clouds, and even covering bushes with their very fleshy white forms (spotted with black), as they come to rest. Their wings when perched are held over the body and can not be folded as is the case with most insects.

Mating takes place on the wing and copulating pairs often fall to ground or onto the water surface. After mating the female deposits her eggs in the water, either dropping them through, brushing them off on the surface, precariously landing to push them through, or crawling down some emergent plant or stone. They quickly lose energy, ending up on the surface of the water where most become food for fish lurking beneath, and hence the appeal of this annual phenomenon of the hatch when the “mayfly is up”, resulting in excellent angling conditions and a frenzy of activity. Other wildlife benefits also, with aerial predators such as dragonflies and birds joining in the feast.

Summer spectacle

So as summer arrives let us consider the fascinating lives of some of our smaller wild creatures which remain hidden and secretive. Then they either erupt in spectacular numbers to draw our attention, and that of a many other wild forms to their showy presence and the availability of a fantastic nutritional feast, or perform more vocal un-missable aerobatic displays to declare their arrival and presence for another season. And it does not all happen in the countryside, but often in the urban environment, where less effort is required, but yielding equally good results and great pleasure and satisfaction.

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