GULDEMOND A, LOMMEN J & LEENDERTSE P (2021) Pesticides in the Barn Swallow Hirundo rustica in the Netherlands. LIMOSA 94 (3): 112-123.

Barn Swallows are insectivores birds, typically foraging in and around their breeding places (such as stables), farmyard and surrounding fields. Here, they can get contaminated with various pesticides, as well as along their migration routes and wintering sites in sub-Saharan Africa. In this study, we examined pesticides in various samples of the Barn Swallow. In summer 2015, a total of 28 samples of nonhatched eggs (N=66), dead juveniles (N=30) and one dead adult Barn Swallow (N=1) were collected on 16 locations throughout the Netherlands (Tab. 2). In total 14 different pesticides were found: five insecticides, one insect repellent, four fungicides, three herbicides and one synergistic substance. Dichlorodiphenyltrichloroethane, commonly known as DDT, was the most widespread pesticide found (in 89% of the samples). Number of pesticides found increased from eggs to juveniles and adult. Measured concentrations of pesticides were generally lower than 0.10 mg/kg. The highest concentration found was DDT: 1.90 mg/kg in the adult bird (Appendix 1). This concentration is likely below the threshold to influence the thickness of the eggshell or to have an acute toxic effect for Barn Swallows. There are several routes suggested on how Barn Swallows might get contaminated by pesticides. One possible contamination route is through fly spray in stables, as suggested by the presence of piperonylbutoxide and permethrin (a commonly used combination in fly sprays) found in a juvenile and adult sample. Various insecticides, fungicides and herbicides are possibly ingested by Barn Swallows via contaminated insects. Another route of contamination might be through feathers of chickens, which are used in Barn Swallow nests. The insecticide cyfluthrin, which is used against poultry red mite, was found in egg samples only. There was one pesticide found that is forbidden in Europe, namely the insecticide novaluron, albeit this pesticide is still used in e.g. South Africa. This suggest that birds can be contaminated by this pesticide on their wintering grounds in Africa (Tab. 2). More research needs to be conducted on the potential effects of mixtures of pesticides on for instance condition and survival of juvenile and adult Barn Swallows, to elucidate their toxicity

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