By Steve Westerman

Wharfedale Naturalists Society

A FEW weeks ago, swallows and swifts returned from their migratory travels (see Nature Notes, July 2, 2020). Recently I have spent some hours by the River Wharfe watching (and trying to photograph) these fly-catching birds.

For a couple of days, in one particular location, swallows were present in numbers. Accompanied by some sand martins, they flew up and down the river, close to the water. I struggled to see what they were feeding on.

One blurry photograph seemed to show a mayfly being taken, although they weren’t obvious in the air. Were they emerging from the water? A few days later I could see small ‘clouds’ of midges hanging over the water. Perhaps these had been the target.

The swallows seemed to be feeding mostly while flying in one direction, using the prevailing breeze as a means of reducing their speed over the water.

Occasionally one would dip to the water’s surface, and make contact, presumably while taking an insect.

Male swallows’ tails are an important indicator of ‘fitness’. Females prefer males with tails that are longer, more symmetrical, and with more pronounced white markings.

A few days later, in the same place along the River Wharfe, and things had changed. The swallows had mostly disappeared, but there were many swifts flying there. As is typical, they generally flew higher. On these days, they were often at tree-top height, although sometimes lower, and occasionally close to the water.

Swallows and swifts appear similar in a number of respects. There are some obvious similarities of physical form, they both feed on airborne insects, and both make enormous migratory journeys.

However, there are also some striking, and perhaps surprising differences. Swallows are passerines, perching birds. They can sometimes be seen sitting on telephone wires, and the like. Although not their usual modus operandi, if needs be, or perhaps if opportunities arise, they are also capable of foraging amongst vegetation.

In contrast, swifts belong to the order of apodiformes, and are poorly equipped for perching or manoeuvring on land. They have particularly short legs for their body size and the arrangement of toes (four forward facing, but with outer toes rotating) is only really suited to clinging to vertical surfaces. They spend the vast majority of their lives, including sleeping, on the wing. Nesting is the notable exception, although other brief interruptions to flight have been noted, possibly due to bad weather. It has been suggested that these extremely efficient fliers can cover more than 124,000 miles in a year.