Species up­date

House Mar­tin re­search is vi­tal to bet­ter un­der­stand de­clin­ing breed­ing num­bers – and you can help, ex­plains Kate Risely

Bird Watching (UK) - - Contents - KATE RISELY’S Kate Risely is the Bri­tish Trust for Or­nithol­ogy’s Gar­den Bird­watch Or­gan­iser

The BTO want your help in mon­i­tor­ing House Mar­tin nest boxes – find out why

ONE OF THE plea­sures of spring is watch­ing the House Martins busily gath­er­ing mud from the lane near my front door – in dry spells I keep a muddy pud­dle topped up with wa­ter for this pur­pose! I don’t know where the colony is, but they aren’t thought to travel more than a few hun­dred me­tres to gather nest­ing ma­te­ri­als, so they can’t be far away. Each cup nest re­quires a thou­sand mud pel­lets to build, mean­ing a thou­sand round trips to a suit­able muddy area. It’s per­haps not sur­pris­ing that they take short cuts when they can, of­ten choos­ing to ren­o­vate old nests, or steal­ing mud from their neigh­bours’ con­struc­tions! Orig­i­nally, of course, they would have nested on rock out­crops, but across much of Europe they have fully shifted to nest­ing on build­ings, and, here in the UK, there are only a few colonies in ‘nat­u­ral’ sites. They tend to stay faith­ful to the colony where they were hatched, though fe­males are more likely than males to move to new sites. How­ever, they don’t seem to stay faith­ful to the same mate, of­ten pair­ing up with a new part­ner each year, and even switch­ing part­ners dur­ing the breed­ing sea­son, es­pe­cially if their first nest­ing at­tempt was un­suc­cess­ful. They will have two or three broods dur­ing the sea­son, with ju­ve­niles from the first brood of­ten help­ing to feed their younger sib­lings from later broods. Dur­ing the breed­ing sea­son adults and full-grown fledglings will roost overnight in the nests or nearby, but some birds may sleep on the wing high above the colony. Ringers have re­ported birds de­scend­ing from high above in the pre-dawn, which, when caught com­ing in to the colony, were freez­ing cold to touch. This may give some clues as to their win­ter­ing habits; while they are known to win­ter across a wide swathe of Africa, they are not of­ten seen in low­land ar­eas, and it’s thought they spend much of their time in very re­mote high­lands or for­ag­ing at high al­ti­tudes. It’s been spec­u­lated that their unique feath­ery feet might be an adap­ta­tion to the cold! Their win­ter­ing ar­eas and habits re­main among the un­solved mys­ter­ies of bird mi­gra­tion stud­ies; more than 400,000 House Martins have been ringed in the UK, and while this has given us valu­able in­for­ma­tion on sur­vival and re­turn rates, it has not helped pin­point their win­ter­ing grounds, as only one Bri­tish-ringed House Mar­tin has ever been re­cov­ered south of the Sa­hara. Track­ing de­vices are as yet too large to use safely on House Martins. The BTO’S bird mon­i­tor­ing pro­grammes in­di­cate that we have lost around 70% of our House Martins since the 1970s, and this trend has con­tin­ued to be over­all down­wards in re­cent years. Many rea­sons have been sug­gested for these de­clines, in­clud­ing the ef­fects of rain­fall on mud for nest­ing, and de­clin­ing in­sect num­bers on the breed­ing grounds, re­sult­ing in a lack of food for chicks, as well as prob­lems on mi­gra­tion. In or­der to bet­ter un­der­stand House Mar­tin breed­ing num­bers, and the rea­sons for changes, the BTO is cur­rently run­ning a large-scale House Mar­tin Sur­vey. This started with ran­dom-site nest counts in 2015 to quan­tify num­bers of breed­ing pairs, fol­lowed by nest ob­ser­va­tions in 2016 to look at breed­ing ecol­ogy and habi­tat pref­er­ences. Any­one can ob­serve a House Mar­tin colony this year to help us learn more about what fac­tors af­fect House Mar­tin num­bers, and help us pin­point the stage in the life cy­cle that is driv­ing these de­clines.

The BTO’S bird mon­i­tor­ing pro­grammes in­di­cate that we have lost around 70% of our House Martins since the 1970s, and this trend is con­tin­u­ing

RE­SEARCH You can help ex­perts un­der­stand pop­u­la­tion de­clines by mon­i­tor­ing House Mar­tin nest sites

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