One of my favourite birds is the swift and every year I look forward to their return to the skies above Berkshire in May. They are amazing creatures and yet we might lose them from our skies in my lifetime.
As soon as it is able to fly, a young swift will launch itself from its nest and will not touch down again for 2 to 3 years. This means that they eat, drink and sleep while flying. That young bird will soon begin its first migration travelling more than 7000 miles to spend our autumn and winter in Africa south of the Sahara. These young birds only return to the UK in their second year and will start to try and find a vacant nest site in, or near, the colony where they were born.
Swifts can live for up to thirty years, and once they have found a mate they will remain faithful to that partner for life and will try and return to the same nest every year. When they are not sitting on eggs, they will be flying up to 500 miles a day to feed themselves and their swiftlets. They feed high in the sky catching insects stirred up by the wind, often at the front of rainclouds or storm systems. A swift can catch up to 10000 insects a day and can store them in a throat pouch to take back to the nest and feed their family. In its lifetime, a single swift could fly about 2 million miles and eat more than 100 million insects! And all that without stopping to rest on the ground or in a tree.
One of the most spectacular things about swifts is when they form a “screaming party”. Tens of swifts will gather, usually on a warm still evening, and fly at roof-top height at speeds of up to 60 kilometres per hour performing impossibly sharp turns as they do so. Some of these racing swifts scream creating an audio and visual spectacle that reminds me of summer holidays, and particularly of watching them from the garden of my grandparent’s house in Weymouth. It is believed that these screaming parties are mostly made up of younger birds demonstrating and honing their flying skills.
Unfortunately swift numbers are in decline. We have lost 60% of the UK breeding population of swifts between 1995 and 2020. If this rate of loss continues, swift screaming parties could be just a memory. The latest research is suggesting that the main problem is a reduction in the rate of survival of young birds. Adult swifts seem to be living as long as ever, but not enough young birds are reaching breeding age to keep the population stable. There are two factors that may be important here: the availability of insects near the nest site; and the increased variability of weather.
Swiftlets are able to go days without being fed by going into a state of torpor. This means that they can live through periods of bad weather when their parents are unable to get out of the nest or unable to return regularly with food. Once the young swifts have left the nest they have to feed themselves and they do not go as far in search of food as the adult birds, so are more susceptible to a local lack of insects. They also need to be able to eat enough to fuel them for their first migration.
Swiftlets can also die during cold spells especially if they get cold and wet. In monitored nest sites in England this seems to be happening increasingly often. An increase in unsettled spells in the summer may be one of the consequences of climate change for the UK.
Traditional swift nest sites under our roofs are lost when buildings are improved. However, swifts will use specially designed nest boxes. There are also swift bricks that can be included in new buildings without any impact to the people living or working in those buildings. The latest research suggests that swifts need nest-boxes in, or near, existing colonies that are designed to give the young a better chance of surviving our increasingly changeable summers.
It is also suggested that green-spaces near swift colonies should be managed in a way that helps their preferred insect prey species. For example, traditional flood meadows are a source of many more flying insects than the equivalent area of drained and pesticide-treated farmland.
If you are lucky enough to be somewhere with swifts flying overhead, stop and enjoy the aerobatic display and maybe spare a thought for how far those birds have flown and what they have seen during their lives. You can find out more about swifts here - https://www.bto.org/understanding-birds/birdfacts/swift.
(Images courtesy of the RSPB - https://www.rspb.org.uk/ )