Swifts are ‘masters of the air’ that need hu­man in­ter­ven­tion to help re­verse their steep, 20-year UK pop­u­la­tion de­cline

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THE SEA­SON OF re­turn­ing spring mi­grants is a spe­cial time, but I most look for­ward to see­ing my first Swifts. They are here with us for less than a third of the year, but they are dif­fer­ent from other birds – speed­ing black scim­i­tars, more like minia­ture stealth bombers – and leave a strong and last­ing im­pres­sion dur­ing their short stay. Their charged power and fragility is per­fectly cap­tured in Ted Hughes’s poem Swifts: “A bo­las of three or four wire screams / Jock­ey­ing across each other / On their switch­back wheel of death / They swat past, hard-fletched”. Not lan­guage that could ever be used to de­scribe our chat­ter­ing, gen­tle Swal­lows and House Mar­tins. They may be masters of the air, never land­ing from one year to the next, but they are en­tirely de­pen­dent on us for safe nest­ing sites. In the past they would have used cav­i­ties in rocky cliffs and dead trees, as they still do in other parts of their world range, but in this coun­try they now only nest in our roof spa­ces. The nest it­self is rudi­men­tary, a shal­low cup of grass and feath­ers, col­lected in flight and ce­mented to­gether with the birds’ saliva. They are so­cial and ex­tremely site faith­ful, un­will­ing to colonise new sites un­less they see other Swifts al­ready in res­i­dence. This re­liance on the built en­vi­ron­ment, with no re­quire­ment for veg­e­ta­tion, is re­flected in their dis­tri­bu­tion, with con­cen­tra­tions in towns and cities. Young Swifts in the nest have to put up with harder con­di­tions than other nestling birds. The adults col­lect aerial in­sects at high al­ti­tudes, but they are un­able to for­age in rain­storms, and fly im­mense dis­tances to cir­cle and avoid low pres­sure sys­tems, of­ten fol­low­ing be­hind weather fronts to ar­eas of warm, ris­ing air that are rich in in­sects. In un­set­tled weather, they may be away from their nestlings for many days, track­ing favourable air masses as far as Ger­many. Back at the nest, the young birds set­tle into a tor­por, re­duc­ing their body tem­per­a­ture and me­tab­o­lism un­til the adults re­turn. Be­cause of this, Swifts have an un­usu­ally vari­able in­cu­ba­tion time, with nestlings spend­ing up to eight weeks in the nest, rather than the two or three weeks nor­mal for smaller birds. While most of our com­mon birds can be mon­i­tored by sim­ple counts of adults NESTLINGS A rare look into the ‘un­seen’ world of a Swift nest with young­sters The BTO runs vol­un­teer sur­veys to mon­i­tor and ex­plain changes in bird pop­u­la­tions. To find out more about the Wa­ter­ways Breed­ing Bird Sur­vey visit present on ter­ri­tory in the breed­ing sea­son, Swifts have no ter­ri­to­ries to speak of, and it can be hard to get mean­ing­ful fig­ures in or­der to com­pare year-to-year changes. A fur­ther com­pli­ca­tion is the fact that they do not breed un­til they are four years old, so a size­able pro­por­tion of the in­di­vid­ual birds that we see are non-breed­ers. De­spite th­ese un­cer­tain­ties, re­sults from the Breed­ing Bird Sur­vey in­di­cate that steep de­clines have oc­curred in the UK over the last 20 years. Due to th­ese de­clines, this species was moved from green to the am­ber list of con­ser­va­tion con­cern in 2009. As long-dis­tance mi­grants, win­ter­ing south of the equa­tor, Swifts are sus­cep­ti­ble to fac­tors in­flu­enc­ing their mi­gra­tion and win­ter­ing grounds, em­pha­sis­ing the need for in­ter­na­tional re­search. Here on their breed­ing grounds, mod­ern build­ing de­sign and re­fur­bish­ment of older roofs can ex­clude Swifts from their nest sites and may be con­tribut­ing to pop­u­la­tion de­cline. The pro­vi­sion of nest­boxes and in­te­gra­tion of po­ten­tial nest sites into new build­ings and ren­o­va­tions may there­fore be of crit­i­cal im­por­tance for Swift pop­u­la­tions.

Kate Risely is the Bri­tish Trust for Or­nithol­ogy’s Gar­den Bird­watch Or­gan­iser

Young swifts in the nest have to put up with harder con­di­tions than other nestling birds. Adults can be away from their nestlings for many days

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