Most songbirds use a nest for just a single clutch or season, then build a new one – if they survive to breed again. But one study showed that most swallows returned to the same colony, with 44 per cent of pairs reoccupying the same nest. “This is remarkable given the length of a swallow’s return migration from its wintering grounds in South Africa,” says Rob Robinson, associate director of research at the BTO. Robinson has studied this iconic species’ unusually strong nest-faithfulness, a phenomenon called philopatry.
What’s so special about the scruffy-looking mud-and-saliva cups that swallows plaster to beams and walls? The answer, says Robinson, is that the construction takes a lot of effort, requiring an average of 1,300 trips to gather enough pellets of material. Moreover, in her classic 2006 monograph The Barn Swallow, Angela Turner cites a Danish study that found males typically do around a quarter of the work, with the most attractive, longest-tailed individuals being the least helpful to their mates.
As a result, it’s well worth returning to last year’s nest rather than starting afresh, especially if you’re a female that has just flown 10,000km from Africa and is now using up valuable fat reserves to form a clutch of four or five eggs. A good nest may be reused for 10–15 years by a series of different pairs.
Do you have a wildlife question you’d like answered? Email your question to firstname.lastname@example.org or post it to Q&A, BBC Wildlife Magazine, Immediate Media Company, 2nd Floor, Tower House, Fairfax Street, Bristol, BS1 3BN