Using citizen science to assess drivers of Common House Martin breeding performance
Author(s): Kettel, E.F., Woodward, I.D., Balmer, D.E. & Noble, D.G.
Published: October 2020
Digital Identifier No. (DOI): 10.1111/ibi.12888
House Martin numbers in the UK have declined by 39% over a 25 year period, but it is unclear why. This small hirundine is a summer visitor that spends the winter months in an unknown part of sub-Saharan Africa, returning to build their cup-shaped nests under the eaves of buildings during April and May. In the 2016 and 2017 breeding seasons, BTO ran the House Martin Nest Study which involved members of the public monitoring the breeding behaviour of House Martins nesting close to where they lived.
The findings of this survey have just been published in the journal Ibis. They show that House Martins arrive earlier in the east of the UK and begin breeding earlier than birds nesting in the west, possibly a result of drier weather in the east. Birds using old nests from previous years or artificial nests also have greater breeding success than those that building nests from scratch. Furthermore, birds that build nests on PVC as opposed to brick, concrete or wood have much lower breeding success, with nests more likely to collapse on the PVC substrate. House Martins breeding in an agricultural environment are also less successful than those breeding in a suburban setting. The study also reported the first confirmed triple broods in the UK; whilst pairs of House Martins have been recorded undertaking three nesting attempts in a single summer further south in Europe, this had not previously been observed in the UK.
The research, which identifies factors potentially influencing House Martin population trends, has direct conservation applications for this declining species. One simple recommendation from the study's results is to install artificial nesting cups to save birds around 10 days of nest building time when they return from migration, especially on buildings wtih plastic soffit. The results also suggest that old nests should not be cleared for similar reasons.
Many hirundine (swallows and martins) species are declining throughout their ranges. The Common House Martin Delichon urbicum is a migratory hirundine that breeds throughout Europe but has shown recent declines in some parts of the UK, particularly in the south. We conducted a large-scale citizen science survey to assess how the breeding performance of House Martin, measured by the number of attempted broods and nest success, is influenced by nest-specific, landscape and weather factors. Pairs in eastern parts of the UK started breeding earlier than those in the west, and breeding performance was higher in eastern regions. There was no effect of latitude on either aspect of breeding performance, so our measures of breeding performance alone do not help to explain differences in population trends across the UK.
The probability of attempting multiple broods and producing successful nests was higher in previously used nests compared to newly-built nests, and in artificial nests compared to natural nests. Nests built on plastic soffits of buildings were less likely to be multi-brooded and less likely to be successful compared to other materials. Suggested conservation measures therefore include discouraging the removal of old nests and encouraging the installation of artificial nests, particularly on buildings with plastic soffits. This study provides a comprehensive insight into the breeding biology of House Martins, and though our findings do not show conclusively that breeding performance is the sole driver of population trends, they go some way to explain declines in House Martins and ultimately provide information that may help conserve this species.
This work would not have been possible without the many volunteers who participated in the House Martin Survey, and the generous donations made to the House Martin Appeal. Special thanks to volunteers Silvia Fowler, Sue Gunn, Laura Cann, Ruth Jones, Lynn Gould, David Hobson and Bob Crook who took part in and provided feedback on the pilot survey.
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