It is a nice coincidence that I’m thinking about a scene concerning the migration of swallows in Defoe’s A Tour Thro’ the Whole Island of Great Britain just at the time when the swallows are returning for the British summer. Early in the Tour, describing the town of Southwold during the first circuit up the East coast, Defoe offers this ‘trifling’ digression:

At this Town in particular, and so at all the Towns on this Coast, from Orford-Ness to Yarmouth, is the ordinary Place where our Summer Friends the Swallows, first land when they come to Visit us; and here they may be said to Embark for their Return, when they go back into warmer Climates.[1]

What follows is Defoe’s memory of previous visit, when he saw swallows flocking for migration:

some Years before …about the beginning of October, and lodging in a House that looked into the Church-yard, I observ’d in the evening an unusual multitude of Birds sitting on the Leads of the Church. Curiosity led me to go nearer to see what they were, and I found they were all Swallows; that there was such an infinite Number that they cover’d the whole Roof of the Church, and of several Houses near. (1:83-84)

Defoe then relates a conversation with a ‘grave Gentleman’ who explains that the birds are waiting for the right wind:

you must then understand first, that this is the Season of the Year when the Swallows, their Food here failing, begin to leave us, and return to the Country, where-ever it be, from whence I suppose they came; and this being the nearest to the Coast of Holland, they come here to Embark. (1:84)

Given that at this time no-one knew for certain the swallows’ ultimate destination, it is perhaps understandable that Defoe presumed that if they are gathering on the coast they are about to fly over the nearest stretch of sea. In fact, we now know a fair amount about the migration habits of Hirundo rustica: rather than cross the North Sea to Holland from Suffolk, it is likely that the swallows were gathering to fly further south to cross the English Channel since their route would take them over France on their journey to Africa. But in the seventeenth and eighteenth centuries the disappearance of birds in winter was a mystery and an active topic of debate. So what were some of the potential contexts for Defoe’s thinking on the migration of swallows?

Tim Birkhead’s wonderful history of bird lore and ornithology, The Wisdom of Birds, spends some time on the various theories concerning the disappearance of birds in winter. Since the classical period, the debate had veered between the conception of migration as we now understand it and the notion that birds, in a condition of ‘torpor’, hibernate inside trees, in rock crevices or even under water. But it was during the seventeenth century that ‘the view that swallows, along with swifts and martins, spent their winters under water  became increasingly entrenched. Sucked into the debate, some claimed to have witnessed the phenomena and seen swallows taken from their watery resting place.’ While by the mid-eighteenth century natural philosophers were increasingly likely to dismiss this, the idea of torpor and underwater hibernation persisted and the debate rumbled on over the course of the century.[2]

From the period most relevant here – the late seventeenth and early eighteenth centuries – there were just a few tracts debating the question of bird migration, including those by John Ray, William Derham and Charles Morton. The move from theories of torpor and submersion to migration can be seen in the work of John Ray: in Ornithology he hedges his bets by including both possibilities for the Swallow: ‘To us it seems more probable that they fly away into hot Countries, viz. Egypt, Aethiopia, &c. then that either they lurk in hollow trees, or holes of Rocks and ancient buildings, or lie in water under the Ice in Northern Countries.’[3] But his later book, The Wisdom of God, focuses upon the idea of the ‘migration of Birds from an hotter to a colder Country, or from a colder to an hotter, according to the Seasons of the Year’ and he suggests, though without any confidence, that birds are reacting to either changes in temperature or food supply.[4] William Derham’s slightly later tract Physico-Theology  also posits that changes in temperature ‘are great Incentives to those Creatures to change their Habitation’, though, like Ray, is still baffled as to exactly why.[5] Most surprising of all is the argument put forward by Defoe’s old Dissenting Academy tutor, Charles Morton. Morton clearly dismisses the theories of submersion and torpor, but only to offer the theory that ‘it is not impossible that divers of these Fowls, which makes such Changes, and observe their Seasons, do pass and repass between this and the Moon.’[6]

By the time the first volume of Defoe’s Tour appeared, The Wisdom of God was in its eighth edition and Physico-Theology in its sixth, and Defoe may also have been aware of his old tutor’s tract on the subject. Defoe has his ‘grave Gentleman’ offer an explanation of the disappearance of swallows not unlike all three tracts, in that it is based upon migration. But the gentleman’s explanation for why they migrate is then amplified by Defoe:

Certain it is, that the Swallows neither come hither for warm Weather, nor retire from Cold, the thing is of quite another Nature; they, like the Shoals of Fish in the Sea, pursue their Prey; they are a voracious Creature, they feed flying; their Food is found in the Air, viz. the Insects; of which in our Summer Evenings, in damp and moist Places, the Air is full; they come hither in the Summer, because our Air is fuller of Fogs and Damps than in other Countries, and for that Reason, feeds great Quantities of Insects; if the Air be hot and dry, the Gnats die of themselves, and even the Swallows will be found famish’d for Want, and fall down dead out of the Air, their Food being taken from them: In like manner, when cold Weather comes in, the Insects all die, and then of Necessity, the Swallows quit us, and follow their Food where-ever they go; this they do in the manner I have mentioned above; for sometimes they are seen to go off in vast Flights like a Cloud; And sometimes again, when the Wind grows fair, they go away a few and a few, as they come, not staying at all upon the Coast. (1:85)

Defoe’s theory of the swallow’s migration carefully rejects one explanation – that they migrate simply in response to changes in the weather – in favour of a more complex one: that their migration is based upon feeding habits which in turn, and only secondarily, are dependent upon the weather. There is a satisfying significance that, on this subject, Defoe breaks ranks with his old tutor (considering Morton’s influence on Defoe’s world-view). Defoe does not offer an accurate account of the swallows’ journey; however, it is important to note that he does offer a substantially more refined explanation of migration than can be found in either Ray or Derham’s tracts. So, while Tim Birkhead relegates Defoe to a footnote, and the scene is a mere diversion in the epic Tour, Defoe’s ‘trifling’ digression is a forthright and carefully thought-through intervention in a small but significant debate in eighteenth-century natural history.