BRINK B VAN DEN (2003) Hygiene measures on modern dairy farms and the fate of Barn Swallows Hirundo rustica. LIMOSA 76 (3): 109-116.

Barn Swallow populations have declined strongly over the past decades as a result of changes in agricultural practice. The number of dairy farms in The Netherlands has fallen from 36 800 in 1992 to 25 800 in 2000, resulting in a substantial loss of breeding opportunities in farm buildings. Production is increasingly concentrated on modern farms where large and open free-stall barns have replaced the smaller, darker and more sheltered tie-stall barns. Increasing pressure on safety and hygiene in dairy production chains has led to a pressure on farmers to prevent swallows to breed in farm buildings like milking stables and milkhouses. During 1992-98, volunteer ringers censused breeding swallows on 18- 102 farms in seven regions in The Netherlands (Fig. 1), determined breeding success and ringed adults and young. The data are used here to assess occupancy rate and breeding success in different types of building, in order to evaluate how changes in dairy farming may affect swallow breeding success.
      Buildings where livestock was present showed markedly higher occupancy by breeding Barn Swallows (45-80%, Tab. 1, Fig. 2) than buildings without animals (24-28%). On dairy farms, occupancy was higher in modern, large cow sheds (free-stall barns), where 15% of all 4810 nests were located, than in small stables and milk and storage rooms, but breeding success was higher in the latter. There was no difference in clutch size or the proportion of second clutches between free-stall barns, milk rooms or milkhouses, and other small buildings (including tiestall barns, sheds with calves, bulls, horses or sheep, and other sheds and garages). However, the number of fledged young was reduced by c. 0.5 in free-stall barns in both first and second clutches (Tab. 2). Factors contributing to the lower breeding output here were problems in anchoring nests to the steel roof beams, easy access for predators and disturbance by House Sparrows Passer domesticus, and exposure to low temperatures and draught in the open barns.
      Concentration of agriculture on large farms has forced Barn Swallows to breed increasingly in free-stall barns, and this has led to a reduction in breeding output. By preventing swallows to breed in the remaining small farm buildings, this problem will be aggravated. It is argued that excluding Barn Swallows from milk and storage rooms, where breeding output is highest, is unnecessary, as the production line from cow to milk tank to dairy factory is well closed and contamination can be avoided.

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