VAN DEN BREMER L, VAN TURNHOUT C, PIERSMA T, NIENHUIS J & DE JONG A (2020) Breeding performance of Dutch House Martins Delichon urbicum. LIMOSA 93 (1): 34-44.

The Dutch breeding population of House Martin has declined with more than 75% since the 1960s, although recently numbers have slightly recovered. For more insight in the underlying causes, a national House Martin nest study to quantify breeding performance was organized in 2018. 88 dedicated volunteers made weekly observations of 1272 individual nests in 104 colonies throughout the entire breeding season (Fig. 1). Mean laying date was 4 June for first clutches and 16 July for second clutches (Fig. 2). The proportion of occupied artificial nests was lower in colonies where more natural nests from previous breeding seasons were present, on sandy soils more than on clay soils (Fig. 3). 87% respectively 76% of the first and second clutches resulted in at least one fledged young. Nest success also differed between soil and nest types, with natural nests performing better on clay and artificial nests better on sand (Fig. 4). In an average of 50% of the nests two successive broods were attempted, with differences between soil and nest types, artificial nests having more second clutches than natural nests (Fig. 5). However, laying date of the first clutch had the strongest effect on the proportion of second clutches: the earlier the first clutch started, the greater the chance that a second brood occurred (Fig. 6). Frequency of nest collapses was higher in second than first clutches, and higher on sandy soils than clay soils (Fig. 7). Of the environmental variables examined, perhaps surprisingly, nest success negatively correlated with the amount of fresh surface water within a 500m radius of the colony, but also with the concentration of neonicotinoids measured in these waters and time of the year.

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